Copyright © 2013 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol 13, 4799–4824, 2013 Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells Nguyen Viet Long1 ∗ , Cao Minh Thi5 , Yang Yong6 , Masayuki Nogami3 , and Michitaka Ohtaki1 In this review, we present the synthesis and characterization of Pt, Pd, Pt based bimetallic and multi-metallic nanoparticles with mixture, alloy and core–shell structure for nano-catalysis, energy conversion, Delivered and fuel cells Here, Pt andTechnology Pd nanoparticles with modified nanostructures can be by Publishing to: TWENTE UNIVERSITY controllably synthesized via chemistry and physics for their uses as electro-catalysts The cheap IP: 130.89.234.194 On: Mon, 03 Jun 2013 15:14:52 base metal catalysts can Copyright be studied inAmerican the relationship of crystal structure, size, morphology, shape, Scientific Publishers and composition for new catalysts with low cost Thus, Pt based alloy and core–shell catalysts can be prepared with the thin Pt and Pt–Pd shell, which are proposed in low and high temperature proton exchange membrane fuel cells (PEMFCs), and direct methanol fuel cells (DMFCs) We also present the survey of the preparation of Pt and Pd based catalysts for the better catalytic activity, high durability, and stability The structural transformations, quantum-size effects, and characterization of Pt and Pd based catalysts in the size ranges of 30 nm (1–30 nm) are presented in electro-catalysis In the size range of 10 nm (1–10 nm), the pure Pt catalyst shows very large surface area for electro-catalysis To achieve homogeneous size distribution, the shaped synthesis of the polyhedral Pt nanoparticles is presented The new concept of shaping specific shapes and morphologies in the entire nano-scale from nano to micro, such as polyhedral, cube, octahedra, tetrahedra, bar, rod, and others of the nanoparticles is proposed, especially for noble and cheap metals The uniform Pt based nanosystems of surface structure, internal structure, shape, and morphology in the nanosized ranges are very crucial to next fuel cells Finally, the modifications of Pt and Pd based catalysts of alloy, core–shell, and mixture structures lead to find high catalytic activity, durability, and stability for nano-catalysis, energy conversion, fuel cells, especially the next large-scale commercialization of next PEMFCs, and DMFCs Keywords: Metal Nanoparticles, Chemical Synthesis, Pt Nanoparticles, Pd Nanoparticles, Carbon, Alloy And Core-Shell Bimetallic Nanoparticles, Surface Structure, Internal Structure, Core–Shell Nanostructure, Electrocatalysis, Catalytic Activity, Selectivity, Catalyst Engineering, Hydrogen, Oxygen Reduction Reaction (ORR), Fuel Cells, Environment Issues, Energy Crisis CONTENTS Introduction 4800 Fundamentals 4802 ∗ Author to whom correspondence should be addressed J Nanosci Nanotechnol 2013, Vol 13, No 2.1 Electro-Catalysis of Platinum 2.2 Pt/Support Catalyst 2.3 Proton Exchange Membrane Fuel Cells 2.4 Direct Methanol Fuel Cells Nanoparticles for Nanocatalysis 3.1 Methods and Syntheses 1533-4880/2013/13/4799/026 doi:10.1166/jnn.2013.7570 4802 4803 4804 4805 4807 4807 4799 REVIEW Department of Molecular and Material Sciences, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1 Kasugakouen, Kasuga, Fukuoka 816-8580, Japan Department of Education and Training, Posts and Telecommunications Institute of Technology, Nguyen Trai, Ha Dong, Hanoi 10000, Vietnam Department of Materials Science and Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan Laboratory for Nanotechnology, Ho Chi Minh Vietnam National University, Linh Trung, Thu Duc, Ho Chi Minh 70800, Vietnam Ho Chi Minh City University of Technology, 144/24 Dien Bien Phu, Ward 25, Binh Thach, Ho Chi Minh City 70400, Vietnam Structural Ceramics Engineering Center, Shanghai Institute of Ceramics, Chinese Academy of Science, Dingxi Road 1295, Shanghai 200050, China Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells 3.2 Metal Nanostructures 3.3 Characterization 3.4 Pt Based Nanostructures: Modification and Improvement 3.5 Structural and Compositional Effects: Improvement of Catalytic Activity 3.6 Opportunities and Challenges Applications Stability and Durability Conclusions Acknowledgments References and Notes 4810 4811 4813 4814 4815 4820 4821 4821 4821 4822 INTRODUCTION REVIEW At present, a very important question arises for leaders, researchers and scientists etc in all over the world: Do low and high temperature fuel cell technologies that can be commercialized on a large scale for our lives in green and sustainable energy? It is truly proved that we can find Long et al the new, durable, and stable catalysts (alloys, metals, and mixtures) that have catalytic activity and sensitivity to liquid fuels, such as hydrogen, methanol, and so on as the same as the noble Pt catalyst.1–10 In the fuel cell reactions, the rates of fuel cell reaction of new catalysts can be much lower than Pt catalyst but their abundance and extremely large sources, which are the important goals of enabling fuel cell large-scale commercialization for transportation, portable, and stationary applications in our lives Recently, U.S Department of Energy Fuel Cell Technologies Program (DOE Program in US), and New Energy and Industrial Technology Development Organization (NEDO Program in Japan) have supported large Research and Development programs (R&D) of fuel cells,9 and fuel cell systems for stationary, portable and transportation applications, such as new fuel cell vehicles The fuel cell program of DOE in 2010 with the funding of about 24,4 million $ was estimated to approval.10 Therefore, next fuel Nguyen Viet Long is the young international scientist in a research project of “Engineering metal nanostructures with high catalytic activity for energy application” with Prof Yang Yong at Shanghai Institute of Ceramics, Chinese Academy of Science He was the Researcher in Kyushu University, Fukuoka, Japan He received B.Sc degree of Physics in Solid State Physics at Department of Physics, Hanoi National University of Education (HNUE), Hanoi, Vietnam He also received M.Eng degree in Semiconductor, and Ph.D degree in Optical and Photonic materials at International Training Institute for Materials Delivered by Publishing Technology to: TWENTE UNIVERSITY Science (ITIMS), Hanoi University of Science and Technology (HUST), Hanoi, Vietnam IP: 130.89.234.194 On: Mon, 03 Jun 2013 15:14:52 He wasCopyright also the Lecturer in general physics in several years, and worked as an official at American Scientific Publishers Department of higher education and training (PTIT), Hanoi, Vietnam Then, he worked as a postdoctoral research fellow in Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya, Japan, and his main research directions of novel platinum and palladium based catalysts in next fuel cells, energy conversion, energy and materials sciences with Professor Masayuki Nogami He worked as a researcher with Professor Michitaka Ohtaki in Department of Molecular and Material Sciences, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Fukuoka, Japan He is also a member of Laboratory for Nanotechnology, Vietnam National University at Ho Chi Minh City Masayuki Nogami was the Professor at Nagoya Institute of Technology (NIT), Nagoya, Japan He received B.S in Materials Sci Eng (Ceramics), NIT (1971), then M.S in Materials Sci Eng (Ceramics), NIT (1973), and Dr Eng at Osaka University (1984) Now he is Professor Emeritus at NIT, President of the Japanese Sol–Gel Society, and Senior Researcher at Nagoya Industrial Science Research Institute Before his joining at NIT, he built his career as Senior Researcher at National Industrial Research Institute in Osaka, Japan, Visiting Research Associate at Rensselaer Polytechnic Institute, USA, and Associate Professor at Aichi Institute of Technology, Japan His main interested scientific area of research are sol–gel process for preparation of tunable new functional glasses and ceramics, Fast proton-conducting materials and their application to fuel cell, Self-assembling of nanoparticles, Optical properties of lanthanide ions in inorganic solids and organic/inorganic hybrid materials, Spectral hole-burning properties of glasses, Nonlinear optical properties of nanoparticles-doped glasses He was the author of more than 400 scientific publications in international peer-reviewed journals, and 20 books So far, he has also presented more than 50 invited lectures in different international conferences Formerly, he had served as a co-editor to the journal Sol–Gel Science and Technology (Springer USA) Due to his research activities, he was Director Chairman of Glass Division in The Ceramics Society in Japan, Visiting Professor at National Engineering College for Industrial Ceramics (ENSCI), France, and Senior Researcher at Laboratory of Science of Ceramic Processes and of Surface Treatments (SPCTS) in French National Research Council (CNRS) In addition, he is now Visiting Professor at Shanghai Institute of Ceramics, Chinese Academy of Science, China 4800 J Nanosci Nanotechnol 13, 4799–4824, 2013 Long et al Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells Yong Yang is the Professor in Shanghai Institute of Ceramics, Chinese Academy of Sciences He received B Eng (1997) and M Eng (2000), Department of Materials Science and Engineering, Shanxi University of Science and Technology, and received Dr Eng (2003), Shanghai Institute of Ceramics, Chinese Academy of Sciences He worked as JSPS postdoctoral research fellow and project Associate Professor in Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya, Japan from 2003–2008 From 2009 to present, he was appointed as Professor in Shanghai Institute of Ceramics, Chinese Academy of Sciences His main interested scientific areas of research are the preparation and self-assembly of metal nanomaterials, catalytic properties and optical properties such as SERS and nonlinear optical properties, surface modification of materials and optical film He was the author of more than 60 scientific publications in international peer-reviewed journals Minh City Physical Society Delivered by Publishing Technology TWENTE UNIVERSITY Michitaka Ohtaki is the Professor into: Solid and Surface Science, Department of Energy and IP: 130.89.234.194 On:ofMon, 03 JunSciences, 2013 15:14:52 Material Sciences, Faculty Engineering Kyushu University, Japan He received American Scientific Publishers B Eng.Copyright (1985), Industrial Chemistry, Faculty of Engineering, The University of Tokyo, and received M Eng (1987), Industrial Chemistry, Graduate School of Engineering, The University of Tokyo He also received Dr Eng (1990), Industrial Chemistry, Graduate School of Engineering, The University of Tokyo He was a research associate (1990–1998), Interdisciplinary Graduate School of Engineering Sciences, Kyushu University From 1998 to present, he was appointed as Associate Professor, Interdisciplinary Graduate School of Engineering, Sciences, Kyushu University His research of very interest has focused on oxide thermoelectric materials for recuperating unused waste heat energy, such as thermoelectric material, oxide semiconductor, energy conversion material, conductive ceramics, thermal conductivity, zinc oxide He has also focused on the systematical development of new oxide thermoelectric modules for mid-to-high temperature waste heat recovery, involving in zinc oxide, layered cobalt oxide, microstructure control, long-term stability assessment In particular, he have developed the modified methods of self-assembly synthesis and properties of inorganic nanomaterials with low-dimensional quantum confinement structures, including low-dimensional nanomaterials, molecular assembly, self-assembly, nano-superlattice, photo-catalyst, magnetism, inorganic–organic hybrid cell technologies, such as PEMFC and DMFC will reach towards large-scale commercialization, from small, compact devices (mobile) or portable devices, large transport vehicles in future This critical review paper presents the Pt and Pt based nano-catalysts for nano-catalysis, direct energy conversion, and fuel cells We have discussed important issues of Pt and Pt based catalysts for nano-catalysis in the certain limit nanosized ranges because of the unique large ratio of surface area to volume, especially in the size limit ranges of 10 nm (1–10) nm, 20 nm (1–20 nm), 30 nm etc with J Nanosci Nanotechnol 13, 4799–4824, 2013 the very ultra-narrow distribution of particle size in the range of 10 nm We have also discussed in the structural and morphological changes of Pt, Pd, Pt and Pd based nanostructures in nano-catalysis Thus, the issues of size, shape, morphology, surface, structure of the as-prepared Pt, Pd, Pt and Pt based nanoparticles as well as the Pt and Pd based mixture catalysts are critical to realize next fuel cells in mass production The alloy and core–shell structures of Pt and Pt based nanoparticles show excellent and potential applications in the rapidly growing technologies and sciences with promising applications of next fuel cells, 4801 REVIEW Cao Minh Thi was the Professor of Mathematics and Physics, and Solid State Physics, in Ho Chi Minh University of Technology, 144/24 Dien Bien Phu, Ward 25, Binh Thanh, Ho Chi Minh City He received B.Sc in Physics, Hanoi National University of Education (HNUE) in 1960 Then, he studied in Mathematics and physics at Lomonosov Moscow State University (1966), and received Ph.D in Mathematics and Physics at Lomonosov Moscow State University (1970) He was also the Lecturer in Physics at HNUE, Vietnam (1960), Lecturer of Faculty of Physics, HNUE in the years of 1972–1975 He was appointed by Vietnamese Leaders of the Vietnam country as vice President of Ho Chi Minh City University of Education or Saigon National Pedagogical University (1975), President of Ho Chi Minh City University of Education (Saigon College) (1981), Associate professor (1984), Deputy Director or Leader of Sector of Education and Training in the entire Ho Chi Minh City (1989) Now He is Vice-president of Vietnam Physical Society, President of Ho Chi REVIEW Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells typically PEMFC and DMFC In addition, we try our best efforts to prove that the issues of the size, shape, morphology, and structure of novel nanoparticles for PEMFC and DMFC have intensively reviewed in respective to their potential applications in nano-catalysis Finally, we propose that metal nanoparticles with very good shape and morphology is controlled in the size range of 10, 20, and 30 nm as well as new nanoparticles of various mixture, Janus, alloy and core–shell structures with or without the use of Pt metal are controlled in the size ranges of 10, 30, and 50 nm, which lead to the realization of large-scale commercialization of PEMFC and DMFC Among above various nanostructures, the core–shell bimetallic catalyst is one of the best selections of large-scale commercialization of next PEMFC and DMFC Among various core– shell nanostructures, core–shell bimetallic nanostructures are very crucial in nano-catalysis There are the trends of creating new alloy based catalysts to replace traditional Pt catalyst In addition, currently the d-band theory has been intensively used to predict and design new, robust and cheap catalysts for fuel cells, typically PEMFC and DMFC Finally, we also emphasize that a new issue of the collapse of the as-prepared nanoparticles in catalytic research is the hot topic for our continuous further studies Long et al Nano-catalysis The size range of 10 and 20 nm … Metal nanoparticles (100) Pt nanoparticles Cube (111) Tetrahedron (111) Highest effect of catalytic properties Octahedron (h k l) Strongest quantum-size effect in nano-catalysis Nanosized ranges: • 10 nm • 20 nm • 30 nm Sphere Shaping nanoparticles in the entire scale from nano to micro (Homogeneous nanosystems) FUNDAMENTALS Fig The ideas of shaping nanoparticles from micro to nano are proDelivered by Publishing Technology to:with TWENTE UNIVERSITY posed the controlled size, shape, morphology, and structure, espe2.1 Electro-Catalysis of Platinum cially cheap 15:14:52 metallic and bimetallic, and multi-metal nanoparIP: 130.89.234.194 On: Mon, 03noble Jun or2013 ticles for nano-catalysis and next fuel cell technologies based on large Copyright American Scientific Publishers In recent years, the Pt nanoparticle catalyst has played a key role in sustainable hydrogen economy The only reason is that Pt is the best catalyst for hydrogen oxidation and oxygen reduction reaction at the anode and the cathode of fuel cells.11 12 At present, most of metal nanoparticles, such as Au, Ag, Pt, Pd, Cu, Rh, Rh, Ru, Ni, Co, Fe, and Mo nanoparticles are used in electro-catalysis The controlled synthesis of noble and cheap metal nanoparticles in the certain size ranges of 10 nm (1–10 nm), 20 nm (1–20 nm), 30 nm (1–30 nm) etc with good shapes and morphologies, such as tetrahedra, octahedra, cube etc (Fig 1), especially synthesis of Pt nanoparticles in the size range of 10 nm for nano-catalysis.13 14 However, among them, Pt noble metal is known as the best electrocatalyst to the fuel cell (FC) reactions, which include hydrogen evolution reaction (HER)/hydrogen oxidation reaction (HOR), oxygen oxidation reaction (ORR), and electro-oxidation of carbon monoxide (CO) with the use of the Pt catalyst on the electrodes of fuel cells.1–10 The issue of CO poisoning on the HOR on the pure Pt catalyst is known To deal with this problem, Pt based bimetallic or multi-metal nanoparticles are used in the catalyst layer Thus, CO poisoning will be controlled by its reduction by second metal, or third metal and so on This is a very good way of avoiding and preventing the anode failure In addition, the new high CO-poisoning-resistant catalysts need to be developed for the anode or fuel electrode It is known 4802 size-quantum effects The high stability and durability of the uniform catalytic nanosystems are achieved with the nanoparticles with polyhedral and spherical morphologies and shapes that the surfaces of the Pt nanosized nanoparticles are very important to nano-catalysis Polyhedral Pt nanoparticles typically show main low-index facets of (100), (110), and (111) They include low-index and high-index facets, typically such as (100), (110), and (111) low-index facets and more high-index (hkl) etc.,15 and the dependence of catalytic activity on the Pt nanostructures.16–18 Here, low-index facets of (111), (100) and (110) of the Pt nanoparticles were proved in high stability and durability in nano-catalysis with electrochemical measurements, and good re-construction in the highest catalytic reactions in various fuel cells.19–21 In hydrogen catalytic activity, the HER on the Pt catalyst is known by the important Volmer, Tafel, and Heyrovsky mechanisms In addition, Volmer-Tafel and Volmer-Heyrovsky mechanisms also occur in the complex combinations of the basic mechanisms The surface kinetics and chemical activity occurring at the electrode surface containing Pt/support catalysts are characterized as follows.1–10 22–24 Pt-Hads → Pt + H+ + e− (1) QDL Charge ↔ QDL Discharge (2) J Nanosci Nanotechnol 13, 4799–4824, 2013 Long et al Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells Pt + H2 O → Pt–OH + H+ + e− Where n, F , k, c, x, , and are constants In addition, n, F , c, and ad indicated the mole (n , Faraday’s constant PtOH + H2 O → Pt OH + H+ + e− (4) (F ), the concentration of O2 (c), and coverage of adsorbed species ( ad ), respectively Here, Gad indicated the weak Pt– OH → PtO + H2 O (5) or strong adsorption We can choose x = and = in the + − 2PtO + 4H + 4e → Pt–Pt + 2H2 O (6) simplification case According to the adsorption degree, the rate may be changed Thus, it may be change from posPt + H+ + e− → Pt-Hads (7) itive value or weak adsorption to negative value or strong To evaluate catalytic activity of the pure Pt catalyst or adsorption It means that the reaction rate declines when Pt based catalysts, we can use an electrochemical active the coverage of intermediates ( ad rises.22–24 surface area (ECSA), which is calculated as QH / 21 × Thus, the further investigations of the HER, HOR, and L Pt Therefore, ECSA can be significantly enhanced by ORR mechanisms in the as-prepared catalyst layer are cruthe use of a low L Pt loading, and a low content of CO cial to obtain the high and large current The nanostrucintermediates generated, and new discoveries of highly tured catalysts need to have high hydrogen solubility and strong hydrogen reactions in the improvements of the Pt reactivity In addition, the fast, sensitive, and stable hydrobased catalysts Clearly, the particle size of Pt nanopartigen desorption/adsorption could be crucial for fuel cells, cles of 10 nm is very crucial in nano-catalysis, energy consuch as PEMFC and DMFC The new catalysts need to version fuel cells, in both PEMFCs and DMFCs because have the high and stable ORR the metal nanoparticles showed very large-quantum and In some interesting works, density functional theory (DFT) calculations of energies of the surface intermedisize effects in the size range of 10 nm The best utiates for a number of metals, such as expensive, rare, noble lization of Pt metal is minimized in this 10 nm range in metals, Pt, Pd, Au, Ag, and so on, abundant, cheap metals, nano-catalysis such as Cu, Ni, Fe, and Co were performed.25 26 In acidic electrolytes, the ORR is observed in two main As a result, an excellent volcano-shaped relationship was pathways as follows established between the rate of the cathode reaction and (8) O2 + 4H+ + 4e− → 2H2 O the oxygen adsorption (Oad ) energy On this useful model involving in d-bandUNIVERSITY center or d-state of various base met+ − + − Publishing to: TWENTE O2 + 2H + 2e → Delivered H2 O2 + 2H by + 2e → 2H2 OTechnology (9) als, the two Pt and Pd elements were predicted to be the two IP: 130.89.234.194 On: Mon, 03 Jun 2013 15:14:52 best choices of cathode materials (Fig 2) It is likely that Copyright American Publishers At present, the phenomena of ORR kinetics and mech- Scientific the Pd based catalyst can replace the Pt based catalyst in the anisms occurring on the Pt catalysts were intensively cathode for ORR in PEMFC and DMFC, avoiding depeninvestigated but a very high over-potential loss observed dence on Pt, an expensive and rare precious metal.25–27 It is indicated that hydrogen peroxide (H O was formed before the formation of water molecules Thus, the very high loadings of Pt must be used in the high requirements of the operation of fuel cells with large current It is known that the Pt catalyst has showed the highest activity to the ORR mechanism In recent years, most of research has led to understand ORR on catalytic systems of Pt designed catalysts using the ultra-low Pt loading at minimal level The issues of the low Pt-catalyst loading, high performance, durability, and effective-cost design in fuel cell systems are very crucial for their large-scale commercialization The cyclic voltammetry (CV) results of various Pt nanoparticles (sphere, cube, hexagonal and tetrahedraloctahedral morphology…) in HClO4 or H2 SO4 showed the strong structural sensitivity of the as-prepared Pt nanoparticles The most basic (111), (100) and (110) planes of high active Pt atoms were confirmed in the active sites of specific catalytic activity, such as in the edges, corners, and terraces.19 For the ORR, the relationship between kinetic current (i) and potential (E) can be investigated as rate expression i = nF kc 1− × exp − ad x exp − F E/RT Gad /RT J Nanosci Nanotechnol 13, 4799–4824, 2013 (10) 2.2 Pt/Support Catalyst At present, Pt, Pd, Pt and Pd based bimetallic nanoparticles with the size of 10 nm and 20 nm are supported Fig Trends in oxygen reduction activity as a function of the oxygen binding energy Reprinted with permission from [25], Nørskov, et al., J Phys Chem B 108, 17886 (2004) © 2004, American Chemical Society 4803 REVIEW (3) REVIEW Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells Long et al (a) on carbon nanomaterials for potential applications in the direct methanol electrooxidation Moreovere, the pure Pt nanoparticles need to be highly dispersed on the supports for obtaining the best catalytic activity in the operation of fuel cells In catalyst engineering, microwave assisted polyol method was used for the preparation of Pt/C, Ru/C and PtRu/C catalysts for the MOR.28 Toward the MOR, PtRu/C electrocatalysts or PtRu-graphitic mesoporous carbons (GMC) were synthesized The results indicated that the role of varios pore sizes of the GMC is especially important in determining the performance of DMFCs.29 In a study, the electrodeposition of Au, Pt, and Pd metal nanoparticles can be performed on carbon nanotubes (CNTs), such as single-walled CNTs (SW-CNTs) via a two-electrode arrangement The issue of Pt/C catalysts was the carbon corrosion by water, which can cause a sig(b) nificant decrease in the catalytic activity in both PEMFC and DMFC In future, we suppose that Pt/novel supports (metals, alloys, oxides, and ceramics) can replace carbon supports with the same catalytic activity as carbon for next fuel cells However, carbon supports are of importance to low-temperature FC catalysts.30 Accordingly, a microwave heated polyol synthesis of Pt/CNTs catalyst for methanol electro-oxidation was presented.31 Because Pt is expensive, Pd is used to replace with Pt in many cases.32–34 Only on adding of a very small amount of Pt (5 at.%), the HOR of the Pd based catalyst can increase Technology to: TWENTE UNIVERSITY is a in the near same as thatDelivered of the pureby Pt Publishing catalyst.35 This IP: 130.89.234.194 On: Mon, 03 Jun 2013 15:14:52 foundation of suitable utilization of noble Pt metal in fuel Copyright American Scientific Publishers cells 2.3 Proton Exchange Membrane Fuel Cells Fig Operation principle of (a) PEMFC, and (b) DMFC 2.3.1 Operation Principle PEMFC has low operation temperature at < 90 C with the use of a polymer membrane electrolyte The components of a fuel cell are an ion conducting electrolyte, a cathode, and an anode, as shown schematically in Figure for PEMFC and DMFC.3 36 The membrane-electrode assembly (MEA) is used in FC technology For example, a fuel such as hydrogen is brought into the anode compartment and an oxidant or oxygen, into the cathode compartment There is an overall chemical driving force for the oxygen and the hydrogen to react to produce water Direct chemical combustion is prevented by the electrolyte that separates the fuel (H2 from the oxidant (O2 The electrochemical reactions occur in a low temperature PEMFC as follows.3–10 35 36 i Cathode 1/2O2 + 2H+ + 2e− → H2 O ii Anode H2 → 2H+ + 2e− (11) iii Overallreaction 1/2O2 + H2 → H2 O (12) The flow of ionic charge through the electrolyte must be balanced by the flow of electronic charge through an outside circuit, and it is this balance that produces electrical 4804 power At present, there are the six most common fuel cells types are PEMFC, DMFC, alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), and solid oxide fuel cell (SOFC) Accordingly, fuel cells are classified on the basic of the types of the electrolytes that they use Therefore, DMFC is a fuel cell as the near same as PEMFC but it uses methanol as the fuel directly on the anode instead of hydrogen or fuel of hydrogen-gas mixture In most cases, Pt or Pd based catalysts are used in low temperature PEMFC and DMFC The use of hydrogen as a fuel has numerous advantages in hydrogen FCs It can be produced from the electrolysis of water or from the reformation of methane, methanol, or other liquid fuels, and when consumed in PEMFCs with oxygen, pure water is the product Among precious metals, Pt is the most active toward the hydrogen oxidation reaction (HOR) that occurs at the anode in PEMFCs To meet a FC of low cost, the Pt catalyst loading must be decreased The two strategies are investigated for reducing the Pt loading in PEMFCs: the fabrication of binary and ternary Pt-based alloyed nanomaterials, and J Nanosci Nanotechnol 13, 4799–4824, 2013 Long et al Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells the dispersion of Pt-based nanomaterials onto high surface area substrates, such as carbon nanomaterials 2.3.2 Pt Based Catalysts use of oxygen treated SWNH catalyst showed catalytic activities higher than using conventional carbon black as electrocatalyst support in PEMFC.43 Recently, an idea of nanosize-Pt-embedded membrane electrode assembly (MEA) has been used to enhance the utilization of Pt in PEMFCs.44 In a PEMFC, the improvements of electrical properties were observed by using CNT in epoxy/graphite bipolar plate.45 Later, a research group showed the shape transformation from Pt nanocubes to tetrahexahedra with size near 10 nm, leading to infuence catalytic activity of Pt nanoparticle catalyst.46 J Nanosci Nanotechnol 13, 4799–4824, 2013 4805 REVIEW At present, Pt is still one of the best choices of next PEMFC because of its good catalytic activity but high cost In addition, carbon monoxide (CO) poisoning occurs at the anode CO can heavily adsorb on the Pt based catalyst and block the hydrogen oxidation To improve the stability and activity of HOR on the pure Pt catalyst, the additions of other metals are performed in the goals of reducing CO poisoning These lead that Pt and Pd based alloy and 2.4 Direct Methanol Fuel Cells core–shell catalysts have been developed In addition, new 2.4.1 Operation Principle CO-tolerant catalyst will be necessarily developed in large amount but low cost Apart from hydrogen fuel, methanol is used in DMFCs So far, the Pt based bimetallic nanoparticles for the Pt It is known that DMFCs have low operation temperature of based bimetallic catalysts have been studied to be Pt–Ru, 40–100 C using MEA technology with a proton exchange Pt–Fe, Pt–Cu, Pt–Mo, Pt–Ni, Pt–Sn, Pt–Re, Pt–W, Pt–Ir, membrane, such as Nafion as electrolyte, and direct MOR Pt–Os, Pt–Rh, Pt–Pd, Pt–Au, and Pt–Ag in the alloy and at the anode of DMFC Methanol offers advantages on 37 core–shell structures The kinds of their mixtures can be hydrogen as a fuel including transportation, storage, and used for the development of PEMFC As a result, catalytic high theoretical energy density Pt is a promising candiactivity and stability of Pt based alloy and core–shell catdate among pure metals for application in DMFCs because alysts are enhanced much better than those of the pure Pt Pt exhibits a highest activity to the dissociative adsorpcatalyst According to the trends, various binary, ternary tion of methanol However, the pure Pt catalyst is easily and quaternary Pt based catalysts among metals of Pt, Ru, poisoned by CO as by-product of MOR at room temperaRh, Pd, Ir, Os, Au, Ag, Cu, Ni, Fe, Co, Mn, Zn, Mo, Sn, W ture.to: The importantUNIVERSITY MOR is discussed in detail The cataDelivered by Publishing Technology TWENTE and so on have been prepared in intensively investigations lyst03layers the15:14:52 sites for electrolysis The membrane is IP: 130.89.234.194 On: Mon, Jun are 2013 for the discovery of higher and, better catalyticAmerican activity Scientific Publishers Copyright the electrical separator and ionic conductor The Pt based and stability.38–40 catalysts are used in the electrodes, both the anode and the However, the complexity of the preparation processes cathode is highly increased The above catalysts can be used on i Anode CH3 OH+H2 O → CO2 +6H+ +6e− various carbon nanomaterials, such as CNT, Vulcan-XC72R etc for the significant enhancement of catalytic activii Cathode 3/2O2 +6H+ +6e− → 3H2 O (13) ity The new catalysts without the use of Pt are being iii Overallreaction considered for avoiding the dependence of the Pt metal The various PtRu alloy/C catalysts were reviewed in the (14) CH3 OH+3/2O2 → CO2 +2H2 O anodes of DMFC They can also used as CO tolerant catToday, hydrogen/oxygen PEMFCs and DMFCs mainly alysts in the anodes of PEMFC In addition, Pt alloyed employ Pt-based catalysts In addition, various DMFCs catalysts exhibitted as improved catalyst for the new cathtechnologies are new technologies at low-temperature less odes of both PEFC and DMFC.38 than 100 C (40–90 C) for portable power generation, Pt-alloy catalysts can be used for the large-scale comespecially in compact mobile devices mercialization of automotive fuel cells.39 The Pt and Pt–Ru based catalyst of mixed metal nanoparticles were discussed in potential applications in PEMFCs, especially Pt/C and 2.4.2 Pt Based Catalysts Pt–Ru/C catalyst using ordered mesoporous carbon for So far, Pt–Ru based catalysts have been successfully used PEMFCs.40 In the catalytic investigations, Pt nanoparticles for the cathode reaction in DMFCs but high cost.36–39 47–50 of 3–5 nm by polyol method in EG were homogeneously The CO poisoning strongly adsorbed on Pt atoms of dispersed on reduced graphene oxide (RGO) nano-sheets the surfaces of Pt–Ru is dealt with by the reduction by for PEMFC, showing ECSA of 33.26 m /g, and high Ru metal atoms, leading to that the poisoned Pt surface 41 power density of 480 mW/cm at 75 C For the combecome very active to the MOR with the bi-functional mon use of Pt/CNFs catalyst for PEMFC, Pt nanoparticles mechanism as follows.47 49 with the size of 2–4 nm were supported on the CNFs.42 In electrochemical impedance spectroscopy (EIS), Ru + H2 O → Ru–OH + H+ + e− (15) PEMFC performance was studied on using single-wall car(16) Ru–OH + Pt–CO → Pt + Ru + CO2 + H+ + e− bon nanohorns (SWNH) to support Pt nanoparticles The REVIEW Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells Long et al Therefore, bi-functional mechanism (or various possible Pt/C was used for fuel cell and catalysis applications.60 multi-functional mechanism for Pt based multi-metal catThere are various methods of preparing Pt based catalysts alysts) for the reduction of CO poisoning is a good way for DMFCs Pt/C composite materials were prepared by of improving the whole fuel cell systems, such as PEMFC the hydrazine reduction of H2 PtCl6 confined to a mixed and DMFC surfactant lytropic liquid crystal (LC)/C mixture with varySimilarly, Pt based bimetallic catalysts are developed ing amounts of water.61 The usefulness of Pt catalyst for for DMFCs They are the kinds of Pt–M catalysts, and SWNT growth under low pressure was demonstrated in M may be Co, Ni, Fe, Cu, and Cr cheap and abundant the preparation of SWNT.62 Pt nanoparticles about 3.0 nm metals Thus, we can use the Pt based mixture catalysts, were successfully loaded inside CNTs.63 In the preparasuch as various binary, ternary and quaternary Pt based tion of porous carbons for hydrogen storage, the hydrogen catalysts Pt–Ru–Rh–Ni based catalyst was prepared for storage capacities of the Pt-doped carbons with a platthe high MOR in DMFCs but high complexity of their inum content of 0.2–1.5 wt% were evaluated by a volcomposition Such the trends simply lead to reduce the Pt umetric adsorption method at 298 K and 10 Mpa,64 and metal used, leading to reduce the total cost of DMFC.51 We need to develop the new Pt based catalysts or the also Pt/CNTs.65 In various Pt base composite catalyst, new catalysts without the use of Pt but they not only Pt–Ru/graphitic CNF nanocomposite catalysts were used resist CO poisoning but also prevent and keep CO poisonin the DMFC anode,66 and Pd and Pt–Pd/C black catalysts ing in MOR at a suitable minimal level as well In CO poifor DMFC,67 as well as Pt–Ru/C multilayer catalysts using soning, intermediates generated by oxygen reduction, such metal-plasma ion implantation for electrical enhancement as hydroxyl and oxide groups can adsorb on the surfaces of of DMFC.68 The controlled synthesis of ordered macrothe nano catalysts, which will decrease the whole perforporous Pt/Ru Nanocomposites catalyst for MOR The mance of the catalytic activity The issue of CO poisoning decomposition and oxidation of methanol on the macrois understood by the mechanisms of Pt–COad and second porous surfaces of Pt100 Ru0 , Pt90 Ru10 , Pt80 Ru20 , Pt70 Ru30 metal atom, third metal atom… with their OH groups, and Pt56 Ru44 catalysts were systemically discussed These e.g., M–OH reacted to form CO2 This characterization is results demonstrate that the three-dimensional ordered a so-called bi-functional mechanism (Pt based bimetallic porous bimetallic catalysts can be potentially used for nanoparticles with alloy and mixture structures) or comDelivered by Publishing Technology to: TWENTE UNIVERSITY developing high 15:14:52 performance DMFC anodic catalysts, plex multi-functional mechanism (Pt based multi-metal IP: 130.89.234.194 On: Mon, 03 Jun 2013 nanoparticles) Thus, a simple solution is to find a suitespecially for the fabrication of microfuel cells on the Copyright American Scientific Publishers able metal again CO poisoning This metal can be used in basoic of compositional effects.69 More importantly, Pt–Pd the Pt based alloy catalysts The known Pt/C, Pt–oxides/C, based catalysts have become very indispensable for MOR Pt–Ru/C, and Pt–Ru-oxides catalysts offer promising canand ORR.70 It is certain that Pd based catalysts were used didates for the new electrodes of DMFC The various caras cathode materials in DMFCs To improve the catalytic bon nanomaterials used are carbon (C) black, C-nanotubles activity of Pd as a cathode catalyst in DMFCs, Pd–TiO2 (CNTs), C-nanofibers (CNFs), C-nanowires (CNWs) etc., catalysts which the Pd and TiO2 nanoparticles were simuland various are oxides, glasses, ceramics, composites, taneously impregnated on carbon The catalytic activities or mixtures, typically WO3 , SnO2 , SiO2 etc.52 as well as of Pd–TiO2 were strongly influenced by the TiO2 con53 Pt/C catalyst (C is single-walled carbon nanohorn) The tent Hence, Pd–TiO2 catalysts showed very comparable issue of Pt/C based catalysts was the carbon corrosion by performance to the Pt catalyst.71 The performance of Pd– water according to time.54 This effect leads to considerTiO2 /C as a cathode material in DMFC was found to ably decrease the catalytic activity of Pt/C based catalysts be similar to or better performance than that of Pt/C.72 The effect of precursor solvent on the properties of Pt was observed The various loadings of Pt nanoparticles were An effect of citrate was found on the Pt state of Pt/C performed by changing solvents of Pt precursor and carblack catalyst for the enhancement of MOR.73 In a combon nanomaterials for their uses as fuel cell catalysts.55 bined method, -Fe2 O3 of 10 nm and Fe–Pt nanoparticles The controlled Pt nanoparticles of 2.2–2.5 nm by using of nm was supported on CNTs by dip-coating process ion liquid, and Pt/C (single-wall carbon nanohorns) catthrough self-assembly FePt/CNT was used for the MOR alysts were used for DMFCs.56 The mechanism of Pt investigated for potential application in DMFCs,74 as well loading on MWCNTs was studied Here, Pt nanopartias the kinds of PtSn/C and Pt3 Sn/C composite based catcles were loaded mainly on and into pores/defects with a alysts for MOR.75 Pt–Re/C (Vulcan carbon) composite 57 size of 2–8 nm The random arrays of Pt nanoparticles based catalyst was also used for MOR in the anode but on glassy carbon electrode (GCE) were prepared for the 58 less than Pt–Ru/C.76 Thus, metal, bimetal, and multi-metal application in the methanol oxidation Pt–Au cluster catbased nanoparticles/carbon, glass, and ceramics supports alyst for DMFCs were also prepared with nanoclusters of 59 are new catalysts for nano-catalysis, energy conversion, nm The Pt nanoparticles of 8–40 nm by cheap ultrasonic method at 4.1 kV, and 5–25 nm at 3.4 kV In this case, and DMFC 4806 J Nanosci Nanotechnol 13, 4799–4824, 2013 Long et al Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells NANOPARTICLES FOR NANOCATALYSIS 3.1 Methods and Syntheses Nanoparticles: Size, shape and morphology Opportunities & Challenges Top-down strategy methods Delivered by Publishing Technology to: TWENTE Physical UNIVERSITY High cost Nanosized ranges: • Photolithography Nanosized ranges: 130.89.234.194 On: Mon, 03 Jun 2013 15:14:52 • 10 nm (1–10 nm)IP: … • Physical vapor • 10 nm (1–10 nm), Copyright American Scientific PublishersDeposition (PVD) (Alloy structure) • 20 nm (1–20 nm), • 30 nm (1–30 nm) … • Laser • 30 nm (1–30 nm) … (Core-shell structures) • Ball milling … (Pt nanoparticles) Atoms Clusters Nanoclusters Nanoparticles Particles Bulk materials Chemical methods • Sol-gel • Electrochemical • Chemical vapor Shape and morphology deposition • Polyol reduction … Low cost • Polyhedra-like nanoparticles • Cube, octahedra, tetrahedra … Bottom-up strategy • Sphere-like nanoparticles • Wire, fiber … • Rod, bar … • Plate, disk … • Flower, branch, belt • Roughness • Flatness • Smoothness • Sharpness • Convex • Concave … Catalysis synthesis techniques Fig The ideas of facile and cheap chemical methods for making metallic, bimetallic, and multi-metal nanoparticles for nano-catalysis in the correlations between size, shape, surface, morphology, and structure J Nanosci Nanotechnol 13, 4799–4824, 2013 4807 REVIEW Metal nanoparticles can be synthesized by various methods of physics and chemistry (Fig 4) Here, the important issues of metal nanoparticles for nano-catalysis are how to control characterization of size, morphology, and structure in the entire size ranges from micro ( m) or microtechnology to nano meter (nm) or nanotechnology The products of nanoparticles by facile chemical methods are very crucial to make new catalysts for FC technology In addition, nano-catalysis of metal nanoparticles plays an important role in the goals of sustainable energy At present, various physical and chemical methods are used to produce nanoparticles and nanomaterials, oxide nanoparticles, bimetal nanoparticles etc It includes ball milling, laser ablation, ion sputtering, combustion flame, microwaveinduced plasma, sol–gel, sonochemical method, radiolysis, ultra-sound, condensation of atomic metal vapor, photochemical method, and thermal decomposition, chemical reduction of precious metal salts, electrochemical reduction and so on, especially the use of ultrasound for the fabrication of catalytic materials In addition, the combinations of chemical and physical methods are used for producing the nanoparticles and nanomaterials.77–80 The ideas of engineered nanoparticles the the entire range from micro to nano offer a lot of potential applications but their effects on health of human body need to be intensively studied in biology and medicine regarding new applications of diagnosis, treatment, and therapy in both animal and human because there are very urgent demands and problems of health and toxicity while the methods of producing various nanoparticles in respective to their related nanotechnologies are well developed.81 A new method to synthesize very active and stable supported metal Pt catalysts: thermo-destabilization of microemulsions.82 In many cases, various inorganic nanostructures can be synthesized via chemistry with promising applications in catalysis, sensors and energy storage.83 In an interesting work of studying the structural change, The small NiO octahedral nanoparticles were prepared by one-pot REVIEW Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells Long et al solid phase synthesis Then, Ni octahedra are synthecarbon nanowalls, two-dimensional carbon nanostructures sized through H2 -annealing of NiO octahedra at various above 120 C.100 Alternatively, the preparation of Pt 84 temperatures In a combination of methods of interest, nanoparticles in heterogeneous solid–liquid system by ultrasound and microwave irradiation.101 Au–Pt–Ag nanoparticle alloys with an average particle size of nm were produced by their ion mixtures after coFigure shows the as-prepared Pt nanoparticles in the reduction of metal ions by femtosecond laser irradiation size range of 10 nm (1–10 nm) with good shape and of aqueous solutions in NH4 OH and PVP as a stabilizer.85 morphology control that can be used for making a good catalyst for next fuel cells, such as PEMFC and DMFC In addition, Pt nanoparticles of 2.5 nm were deposited on because of the largest quantum-size effect, leading to the the WO3 film surfaces at room temperature by sputterstrongest catalytic activity and sensitivity ing The surface coverage of Pt on the WO3 films with The catalytic properties of the as-prepared Pt nanoparhigh photocatalytic activity was found in the decompositicles are strongly affected by the nature of their surface tion of acetaldehyde under visible light irradiation.86 On structure, internal structure, such as roughness, sharpness, the relative effect of protection agents, the Pt nanoparticles flatness, smoothness, porosity, atomic density of particle of 5.4 nm with the protection of PAMAM (isopropanol surface, chemical bonding, chemical and structural change (IPA)-modified dendritic poly(amido amine) (PAMAM)) etc.102 In the ratio of volume to surface, nanoparticles with was prepared.87 In the controlled synthesis, the combined methods with magnetic (MS), mechanical (UT) and ultravarious particle sizes of nm, nm, nm, 10 nm, and sonic stirring (USS) were conveniently used to synthesize 20 nm showed the atom populations of 20, 250, 4000, novel Fe3 O4 –Pt core–shell nanostructures exhibited high 30000, 250000 atoms, but the proportion of surface atoms of 99, 80, 40, 20, and 10%, respectively.103 A nanoparticle electrocatalytic activity.88 Among bimetallic nanoparticles, FePt nanoparticles fabricated by pulsed laser ablation are has the particle size of nm showing the largest number promising candidates for DMFC.89 of surface atoms (99%) for the highest catalytic activity, comparable to larger particles, 2, 3, 5, 10 and 20 nm but The chemical methods prove the ease of application in producing Pt and Pd based metal, bimetal and multithe it is clear that less durability and stability of strucnanoparticles for nano-catalysis and energy conversion, ture This evidence is extremely crucial in green nanoespecially the facile controlled synthesis of Pt and Pd catalysis However, the phenomena of surface attachment, Delivered Publishing Technology to: TWENTE UNIVERSITY nanoparticles by polyol method inbythe range of 10 nm aggregation or agglomeration, assembly, and structural IP:Pt130.89.234.194 On: Mon, 03 Junof2013 15:14:52 polyhedral Pt nanoparticles For the controlled synthesis of nanoparticles, a small changes the as-prepared Copyright American amount the salts of AgNO3 15 90–92 The are very Publishers crucial to their potential application in nanonucleation, growth Scientific catalysis and energy conversion.104 Most importantly, the and formation mechanisms of PVP-Pt nanoparticles in EG are intensively discussed in the sharp and un-sharp phenomenon of natural collapse and self-breaking in the as-prepared naked Pt nanoparticles is also very crucial to nanocrystal structures including cubic and octahedral mornano-catalysis,102 104 107 leading to a significant decrease phologies as well as various irregular morphologies.52 The usual additives can be used for the controlled synthesis of in the catalytic property of catalytic nanosystem, which Pt nanoparticles such as NaI,94 NaOH95 for controlled syninvolves in catalytic activity and sensitivity as well as durability and stability of the as-prepared Pt based catalysts for thesis of Pt nanoparticles In addition, FeCl2 and FeCl3 can next PEMFC and DMFC producing energy with efficient be considered as structure-controlling agent The of Pt preand cheap cost.104 So far, we have successfully synthecursors, available commercial such as H2 PtCl6 , Na2 PtCl4 , K2 PtCl4 etc are used for the reduction reaction by ethylene sized various Pt, Rh,105 and Pt, Pd and Pt–Pd nanoparglycol, alcohols, H2 gas, NaBH4 (sodium borohydride), ticles with polyhedral and spherical morphology,106 and, N2 H4 (hydrazine), Na2 HC6 H5 O7 (sodium citrate), ligand Au, Pt and Pt–Au bimetallic nanoparticles107 with polyhedisplacement method, thermal reduction, photochemical dral morphology under size and shape control by modified reduction, sonochemical reduction etc The stabilizers polyol methods for catalysis and direct energy conversion (dendrimers, surfactants, polymers) are used for protectIn addition, Rh nanoparticles using a probe of malachite ing the Pt nanoparticles Typically, they are PVP, CTAB, green molecules exhibited the high sensitivity for potenblock copolymers, other various ligands.96–98 Cubic Pt tial applications in chemical and biochemical sensing on the basic of surface-enhanced Raman scattering (SERS).105 Nanoparticles of nm were prepared in aqueous hexadecyltrimethylammonium bromide (CTAB) solution by the Similarly, Rh nanoparticles about nm in the range of reduction H2 PtCl6 by NaBH4 reduction The Pt nanoag10 nm were synthesized from dirhodium(II) ethylene glycol tetracarboxylates.108 Certainly, various precious and glomerates of 20 to 47 nm were formed by by a seedmediate growth process.99 In a new synthethic method, cheap metal nanoparticles can be synthesized for very excellent applications in catalysis, biology, and medicine, Pt nanoparticles around nm in size were prepared by typically as Au, Ag, Fe nanoparticles in the therapy for the metal-organic chemical fluid deposition (MOCFD) cancer treatment Thus, metal, bimetal or multimetal based employing supercritical fluid (SCF) Pt nanoparticles were nanoparticles show promising practical applications The dispersed on the surface of aligned carbon nanotubes and 4808 J Nanosci Nanotechnol 13, 4799–4824, 2013 REVIEW Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells Long et al core–shell catalysts are important to create new Pt or Pd Ni, Fe, Cu…) potentially integrated in oxides, cerambased catalysts for developing sustainable and renewable ics, and glasses in continuous research efforts Therefore, energy via various fuel cells Therefore, we can still need scientists need to try to study urgent issues of catalytic to develop novel metal or oxide nanoparticles, nanosized activity, selectivity, durability, and stability of next fuel structures, and various fuel cell materials Similarly, multicell using cheap alloys for replacing Pt metal Here, Pt metal nanoparticles for new catalysts in next fuel cells can clusters, nanoclusters, and nanoparticles are synthesized be synthesized by simple chemical and physical methods by simple polyol method with or without the assistance They can be largely used with the very large amounts in of silver nitrate for the goals of controlling their nanocatalysis, energy conversion, FCs, or promising applicastructures In the nanosized range of about 10 nm or tions in thermoelectric materials as well as biology and 20 nm, Pt clusters, nanoclusters and Pt nanoparticles can medicine with low costs be easily synthesized Therefore, the issues of size and morphology need to be intensively studied in the further catalytic investigations for Pt nanoparticles with the size 3.2 Metal Nanostructures range of 30 nm (1–30 nm) In any confirmations of catalytic durability, stability, and activity of the Pt nanoparAt present, noble and cheap metal nanostructures are of ticle based catalysts In this respect, our research results very importance in various technologies and sciences, such of using a low loading of low weight of Pt metal catas electronics, communications, catalysis, biology, and alyst in novel robust and efficiently designed catalysts medicine We suppose that most of the known products of are one of the best ways for large-scale commercializaAu, Ag, Pt, Pd, Ru, Ir, and Os nanoparticles have been tion of next fuel cells Therefore, the controlled synthedeveloped in the size ranges from micro to nano in the sis of Pt and Pd based nanoparticles are crucial in the good morphologies and shapes The physical and chemreduction of the loading of Pt or Pd catalysts while large ical methods are very crucial to their synthesis.77–80 119 quantum-size or shape effects are still preserved They Similarly, Cu, Co, Fe, and Ni nanoparticles have been syncan be used as the catalytic Pt and Pd shells for importhesized in the various size ranges We suggest that the tant bimetallic nanosystems for the goals of reducing the mixture of different cheap and noble nanoparticles with high costs of fuel cell systems using noble metal catalysts small and large sizes can be the good solutions of new Publishing to: TWENTE In addition, controlled Delivered syntheses ofbymetal, bimetal,Technology multicatalysts for FCs UNIVERSITY In particular, the mixing of Pt or Pd IP: 130.89.234.194 On:inMon, 03 Jun 2013 15:14:52 metal, and multi-component nanoparticles are studied nanoparticles shaped in the ranges of 10 nm and 20 nm Copyright American Publishers catalysis, biology, and medicine Here, we mainly focus Scientific with other cheap metal nanoparticles will be an economon controlled synthesis of novel Pt or Pd based alloy or ical solution of the large-scale commercialization of fuel core–shell nanoparticles or “noble metal based core–shell cells The synthesis of Pt, Pd, Rh, Ru, Au, and Ag, or nanosystems” with noble metals or oxides shells, and their noble metals nanoparticles are successfully accomplished potential applications It is certain that bimetallic or multibut very high costs They have various size ranges of about metallic nanoparticles with novel homogenous alloys and 10 nm, 20 nm, 30 nm, 50 nm, 1000 nm m, up to core–shell nanostructures (Pt–Fe, Pt–Cu, Pt–Ni based cat10 m Similarly, the syntheses of Ni, Co, Fe, and Cu… alysts…) can be synthesized However, at present the sucor cheaper metals nanoparticles are also accomplished We cessful synthesis of homogeneous core–shell nanosystems can produce them with large amounts They possibly have are the extreme challenges to scientists and researchers the certain size ranges of about 10 nm, 20 nm, 30 nm, At present, in scientific works, metals (Pt, Ru, Rh, Pd, 50 nm, 1000 nm m, up to 10 m In particular, Os, Ir, Au, Ag, Fe, Co, Ni, Cu, Mn)109 can be used the synthesis of Pt, Pd, Rh, Ru, Ir, Os, Au, Ag nanoparas new electrode materials for SOFC or PEMFC anodes ticles in the certain size range of about 10 nm, 20 nm through the predictions and methods of quantum mechanwith morphology and shape control that are (i) polyheical calculations and density-functional theory (DFT), and dral, near-polyhedral, cubic, octahedral, and (ii) spherical the uses of Ni metal on electrocatalyst for SOFC or Pt– or near-spherical or quasi-spherical as well as, (iii) rod, Ni alloy catalyst for meeting the requirements of the fiber, wire, belt In particular, the particle size of noble operation of PEMFC.109–113 In various accomplishments, nanoparticles with cubic, tetrahedral, and octahedral polya synergic effect of core–shell bimetallic nanoparticles hedral morphology or truncated polyhedral morphology was discovered in enhancement of catalytic activity and will be controlled in the 10 nm or 20 nm ranges for obtainsensitivity.37 106 113–118 171 172 ing the large “size-quantum” effects for nano-catalysis Accordingly, other authors in the world reported that The crucial issues of size and morphology, structural transthe lattice-strain control of the catalytic activity in dealformations are still controversial to catalysis and fuel cells loying of the core–shell catalysts was studied in the Pt–Cu In a same weight of Pt metal or salts for making Pt catalysts for reducing the Pt loading significantly Thus, nanoparticles, we can make a large number of very small the synergic core–shell effects of Pt or Pd based bimetalparticles of 10, 20, 30 nm, but we can make a small number of very large particles of 100 nm, or more than that lic catalysts as well as dealloying effects of Pt based 4810 J Nanosci Nanotechnol 13, 4799–4824, 2013 Long et al Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells It is clear that a number of large particles in a same weight of Pt is much smaller than that of small particles but the structural durability and stability of the large particles are much better than those of smaller particles.120 Figure shows the ideas of the designed catalysts are proposed with the new nanostructures of metallic, bimetallic, and poly-metal nanoparticles for the catalytic enhancements as well as the high catalytic sensitivity, durability, stability, and safety of the new catalysts in nano-catalysis and fuel cells 3.3 Characterization The shape-controlled synthesis of metal nanostructures is discussed in their potential applications in nano-catalysis, especially in the cases of Pt and Pd nanoparticles for electro-catalysis The uses of metal nanocrystals for the catalytic reactions have been reviewed in both homogeneous catalysis and heterogeneous catalysis on support, for example, in catalytic reactions of hydrogenations.77 121 Today, metal nanoparticles, for example Pt nanoparticles, can be simply synthesized by chemical methods at relatively reasonable and low costs The desirable catalytic and electro-catalytic properties mainly depend their specific nanostructures, or diversity of structures, such as polyhedra, near-polyhedra, cube, octahedra, sphere or near-sphere or quasi-sphere, rod, bar, fiber, wire, flower, branch, etc In particular, the particle size of noble nanoparticles with cubic, tetrahedral, and octahedral polyhedral morphology or truncated polyhedral morphology Nanoparticles for catalysis & energy conversion REVIEW Particles on particles (1) Mixed particles (Small and large) Pt or Pd nanoparticles … Noble metal nanoparticles (10 nm, and 20 nm) Metal nanoparticles: - Cheap metals (Cu, Ni, Co, Fe ) - Noble metals (Au, Ag) Platinum group metals (PGM) Delivered- by Publishing Technology to: TWENTE UNIVERSITY IP: 130.89.234.194 On: Mon, 03 Jun 2013 15:14:52 Copyright American Scientific Publishers • 1-100 nm: 1-10 nm, 1-30 nm, 1-50 nm, 50-100 nm • 100-1000 nm (0.1-1 μm) • 1000-10000 nm (1-10 μm) (2) Pt based core-shell catalysts de-core-shell catalysts, de-alloying catalysts, crystal phase-separation catalysts Bimetal nanoparticles (3) Pt based alloy catalysts (various elements) (4) New catalysts of metals and alloys without the use of Pt (5) Mixture nanoparticles (metal, glass, oxide, ceramic, composite) (SiO2-Pt-CeO2 …) (6) Pt based nanoparticles with ultra-high porosity Fig The ideas of the new nanostructures of the designed catalysts The new methods of designing new catalyst, especially with the use of Pt nanoparticles or Pt nanoclusters on cheap metal nanoparticles The core-shell structure is an economic solution for reducing high cost of Pt J Nanosci Nanotechnol 13, 4799–4824, 2013 4811 REVIEW Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells Long et al are studied by XRD method in a fcc structure as Pt metal, will be controlled in the 10, 20, and 30 nm ranges for which are typically characterized by a limited number of obtaining the large “size-quantum” effects However, the the diffraction peaks of (200), (111), (220), (311), and crucial issues of size and morphology, structural transformations are still controversial to nano-catalysis, energy (222) planes in a limit range of 5–90 for the XRD method conversion and fuel cells The most typical methods of In many works, controlling size, surface, structure, shape, characterizing Pt metal nanoparticles include transmission and morphology of Pt nanoparticles by chemical methods electron microscopy (TEM), high-resolution TEM for the for nano-catalysis are very important to determine recent features of size, shape, morphology and structure, elemenscientific developments of green energy materials.122–124 tal analysis, energy disperse X-ray microanalysis (EDX) and other functions for investigations of their chemical 3.3.2 Structural Effect and bonding changes The final formations of the solution products of the as-prepared Pt nanoparticles are studied by The issues of the size and morphology control of Pt nanoultraviolet and visible absorption spectroscopy (UV/VIS) particles are of importance in nanocatalysis and potenThe limitations of X-ray diffraction (XRD) in the range tial applications in next fuel cells Pt nanoparticles can of about 5–90 degree and other various results are conbe well controlled in the ranges of 10 nm, 20 nm, and firmed in our research with a number of (h k l) planes of 30 nm with high homogeneous size distribution Howfcc structure of Pt metal,90–93 104–107 114 115 125 126 and other ever, in these ranges, the issues of shape and morphology works.122–129 control are much difficult than those of the size Now, Some other analysis methods for characterization of polyhedral shapes and morphologies are achieved at the small and large Pt nanoparticles in the ranges of ranges of 1–30 nm In our research, polyhedral Pt nanopar100–10,000 nm or 1–10 m such as SEM can be used in ticles show the (hkl) indices were observed It shows a our research Electrochemical measurement techniques are fcc structure of (hkl) indices, typically (111), (200), (220), used to analyze catalytic activity and sensitivity, reliabil(311), (222), (400), (311), (420), (422), (333), (511), (440), ity, stability, durability and reproducibility of the now as(531), (442), (600), (620) and (533) or more (hkl).125 126 prepared Pt based catalyst In order to investigate catalytic Therefore, Pt nanoparticles also have surface defects, such activity of the as-prepared Pt, Pd, and Pt–Pd catalysts, as the defects at surfaces, edges and corners Here, varicyclic voltammetry measurements performed atTechnology room Delivered were by Publishing TWENTE UNIVERSITY ousto: surface steps, kinks, islands, terraces, and corners can IP:of130.89.234.194 On: Mon, Jun 2013 15:14:52 temperature with a typical setup three-electrode electrobe03 observed by TEM method However, we only found Copyright American chemical system connected to a potentiostat (SI 1287 Elec- Scientific that somePublishers certain planes of (111), (200), (220), (311) and trochemical Interface, Solartron).104 125 126 The CV cell (222) rings were confirmed in the XRD data despite of was kept in a 50-mL glass vial, which was carefully treated their various shapes and morphologies Recently, the feawith the mixture of H2 SO4 and HNO3 , and then washed tures of low and high indices of Pt nanoparticles have generously with milli-Q water A leak-free AgCl/Ag/NaCl been intensively studied In particular, tetra-hexahedral Pt electrode (RE-1B, ALS) served as the reference All potennanocrystals with high-index facets exhibited high electrotials were reported versus Ag/AgCl The counter electrode oxidation activity The atoms of the high-index planes can was a Pt coil (002234, ALS) The electrolyte solution was be considered as chemical active centers of high catalytic bubbled with N2 gas for 30 before every measureactivity because of a large density of atomic steps and ment, and a N2 blanket was kept during the actual course dangling atomic bonds.127–129 However, the catalytic activof potential sweeping In the measurements, the solutions ities of Pt catalyst showed active centers at the active sites of 0.1 M HClO4 or 0.1 M H2 SO4 are used as the elecin the (111), (110) and (100) main facets The low-index trolytes for the base voltammetry For example, the stock facets of active Pt atoms showed high durability and stasolution of 0.1 M HClO4 can be diluted from 70% conbility The surface atomic arrangements of Pt nanoparcentrated solution (Aldrich) using milli-Q water In our ticles of low and high-index facets are very important research, the potential window between −0 and 1.0 V in nano-catalysis The porous Pt nanoparticles with high with a sweep rate of 50 mV/s was used In order to invesporosity may showed a good activiy in nano-catalysis tigate the methanol oxidation reaction (MOR), the above but durability and stability that may be much less than electrolyte was added with 1.0 M methanol in milli-Q those of stably durable polyhedral-like and spherical-like water The system measurements were cycled and repeated Pt nanoparticles.130 The various shapes and morphologies until the stable voltammograms were achieved of the tetrahedral and cubic Pt nanoparticles were studied for nano-catalysis in solution with different catalytic activity for the facets of (100) and (111) planes.131–134 3.3.1 Pt Nanostructure: Size, Shape, and Morphology The as-prepared Pt nanoparticles with the size range of In order to use the as-prepared Pt nanoparticles as the pure 10 nm in the cubic shapes or polyhedral shapes were Pt catalyst for fuel cells, the issues of controlling Pt nanochemically synthesized by polyol synthesis for the use in structures are of importance At present, Pt nanostructure nano-catalysis The cubic Pt nanoparticles showed a higher 4812 J Nanosci Nanotechnol 13, 4799–4824, 2013 Long et al Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells selectivity to n-butylamine as compared to polyhedral Pt nanoparticles.135 Recently, a new phenomenon was found in the randomly natural collapse and self-breaking in the Pt nanostructures in the case of no any protective polymer agents This phenomenon can lead to the less stable catalytic activity by the structural changes of Pt nanoparticles in the nanosized range of 1–50 nm.103 We suggest that the mechanisms of surface attachment, aggregation or agglomeration and assembly of Pt nanoparticles are very crucial to the issues of dispersing Pt nanoparticles in the matrices of large-area support nanomaterials, such as carbon, glass, oxide, and ceramic It is certain that the Pt nanoparticles can directly combine in the cases with or without the protection of PVP polymer via their various mechanisms, such as random or direct collisions, and common surface attachments among them by aggregation or agglomerate in the entire nanoscale The size effects of metal nanoparticles or engineered 3.3.5 Composition Effect nanoparticles are of importance in nano-catalysis, especially the certain range of about 10 nm (1–10 nm), and of So far, the composition effects of Pt based bimetallic 100 nm (1–100 nm) For Pt nanoparticles, we can obtain nanoparticles or Pt based polymetalic nanoparticles in the largest surface area in the same weight of Pt loadnano-catalysis and fuel cells have been very hard to undering catalyst with their critical size of about 10 nm Thus, stand in the general knowledge In this context, binary, size effect is one of the most important properties of Pt ternary, and quaternary Pt alloy catalysts with Pt, Ru, Os, Delivered by Publishing Technology to: TWENTE UNIVERSITY nanoparticles for catalysis in low-temperature fuel cells In and Ir element for MOR were used in DMFCs Pt–Ru–Os– IP: 130.89.234.194 On: Mon, 03 Jun 2013 15:14:52 our opinion, a new concept of the standard Pt catalyst is Scientific Ir catalystPublishers showed the best catalytic activity and stability Copyright American proposed for the “polyhedral” Pt nanoparticles of around much better than Pt–Ru.137 138 Most of novel Pt based cat10 nm In addition, the utilizations of low Pt loading cataalysts are prepared by the variations of atomic concentralysts are performed in new Pt based catalysts We suggest tions of noble Pt and other metals or multi-components for that the size involves in the durability and stability of the further investigations of their electro-catalysis The deterias-prepared nanoparticles oration of the as-prepared catalysts within the PEMC and DMFC because of the CO poisoning in anode In this case, 3.3.4 Shape and Morphology Effect we can use Pt based alloy and mixture catalysts to decrease CO poisoning The surfaces of Pt nanoparticles were studied in the size range of 10 nm, 20 nm, and 30 nm Here, the polyhe3.4 Pt Based Nanostructures: Modification dral Pt nanoparticles were observed in their sharp and and Improvement smooth morphologies In addition, the convex and concave roughness morphologies are confirmed in the size range of 3.4.1 Alloy Bimetallic Nanostructures 10 nm, 20 nm, and 30 nm The very high complexities of Pt based catalysts composing of bimetallic nanoparticles surface roughness of Pt nanoparticles are the research topare used in the FC reactions because of a significant catics of bonding and chemical changes at the nanoscale limalytic enhancement Here, the issues of homogeneous size itation We think that large particles of the certain ranges and morphology of bimetallic nanoparticles are crucial of 100 nm, 1000 nm… up to 10 m or etc have the They need to be homogeneously supported on the supdurability and stability much more than the small partiport materials, such as carbon materials, glasses, ceramcles of 10 nm, 20 nm, and 30 nm However, the high ics, oxides etc for the highest catalytic characterization catalytic activity of small particles is much more than that The typical Pt based bimetallic nanoparticles are of large particles The mixing solution of small and large Pt–Pd, Pd–Rh, Pt–Ru, Pt–Au, Pt–Ag, Pt–Fe, etc.37 138 139 particles can give the durability and stability as the high In generel, bimetallic nanoparticles also have various dispersion in the Pt based as-prepared catalysts for fuel nanostructures (alloy, core–shell structure, mixture) for cells The Pt catalyst of high catalytic activity can be used the fast development of new FC materials accordwith the prepared polyhedral or spherical Pt nanopartiing their preparation processes In addition, Pt–Ni,140 141 cles of from to 10 nm, or from 10 to 20 nm etc for J Nanosci Nanotechnol 13, 4799–4824, 2013 4813 REVIEW 3.3.3 Size Effect nano-catalysis and FC reactions In particular, the popular as-prepared polyhedral-like and spherical-like Pt nanoparticles are very neccessary to be intensively studied On these issues of shapes and morphologies, catalytic activity, durability, and stability can be confirmed in the quantumsize, shape, and morphologies effects.136 The very high roughness of the as-prepared Pt nanoparticles is confirmed in our research The extremely high crystallization degree of the as-prepared Pt nanoparticles as Pt metal bulk material was discovered in the HRTEM evidences of these nanoparticles grown from the homogeneous EG solvent At the same time, the sharpness of shape and morphology of Pt nanoparticles is also observed Both the high roughness and the high sharpness of the as-prepared Pt nanoparticles according to their chemical and bonding changes are crucial to understand the nature of nano-catalysis in further studies It is noted that making high roughness of the as-prepared Pt nanoparticles can lead to achieve high catalytic activity and sensitivity REVIEW Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells Long et al noble metals-oxides core–shell nanoparticles The new Pt–Co,142 143 Pt–Cu144 145 Pt–Sn146 , Pt–Pb147 with various nanostructures, such as alloys, core–shell structures, and directions of study of noble Pt metal catalyst, and Pt/cheap mixtures are of interest in new catalysts Typically, FePt metals based catalysts with supports are focused on carNanoparticles become a new class for nano-catalysis.148 149 bon nanomaterials, carbon nanotubes (CNTs), carbon nanoAt the same time during annealing process, the prevention fibres (CNFs)…, Pt/oxides, Pt/glasses for catalysis in of coalescence of FePt Nanoparticles assembled by conpotential applications in next fuel cells At present, new vective coating needed to be carefully done.149 Here, the Pt based catalysts based on a mixture, Pt nanoparticles synthesis of Co–Pt nanoparticles was presented in the abil(1–10 nm) with large cheap metal nanoparticles, such ity of enhancing the catalytic activity.150 Here, researchers as Cu, Ni, Co, Fe are very crucial, and new to scienwant to use cheap metals for reducing Pt catalyst loading tists It means that a combination of metallic and bimetaland the high costs of PEMFCs, DMFCs or various FCs lic nanoparticles can be used as new catalyst materials At present, multi-metal nanoparticles with homogeneous for FCs, such as novel metal-bimetal nanoparticles and size and morphology can be prepared by polyol method, or nanostructures various physical and chemical methods They are Pt based multi-metal alloy catalysts with high catalytic durability 3.5 Structural and Compositional Effects: and activity but complexity of their preparation processes Improvement of Catalytic Activity The new research directions are focused on the controlled syntheses of Pt based multi-metal core–shell catalysts with 3.5.1 Synergic Effects a significant reduction of the weight of Pt metal despite of big challenges In this context, Pt–Pd based multi-metal A synergistic effect was found in the enhanced catalloy catalysts are of importance in low and high temperaalytic activity of Pt based alloy and core–shell bimetallic ture DMFCs and PEMFCs Thus, Pt–Pd based multi-metal nanoparticles This effect leads to an excellent catalytic core–shell catalysts can also be prepared Among new Pt enhancement in the case of Pt–Pd core–shell nanoparticatalysts, Pt–Ni based alloy and core–shell catalysts are cles In catalytic activity, the metal shell element provides intensively studied However, the issues of complexity of catalytic sites It is known that the metal core element multi-metal and multi-component can be simplified by the gives an electronic effect, a ligand effect, on the shell eleways of synthesis and Delivered preparation by processes A bigTechnology chalment the UNIVERSITY surface atoms of the shell are coordiPublishing to:because TWENTE lenge is to find new and cheap catalysts (cheap cost), nated to the2013 core 15:14:52 in the catalytic FC reactions Of course, IP: 130.89.234.194 On: Mon, 03 Jun which can reduce the loading of Pt Copyright catalyst (high cost) or Scientific American both the Publishers core and the shell in the ranges of 10 nm, non-Pt catalyst 20 nm, and 30 nm are crucial to control the catalytic properties in FCs The better suppression of adsorbed 3.4.2 Core–Shell Bimetallic Nanostructures: poisonous species was proved in Pt based core–shell Solutions of the Very Thin Pt Layers bimetallic nanoparticles and nanostructrues, which modify electronic band structure to create the better surface In order to discovery a new catalyst for FCs, catalytic adsorption It is proved that the evidences of a synerenhancement and activity need to be investigated through gic effect or bi-function effect discovered are proved in size and shape effects, structure effects, hydrogen-catalyst bimetallic nanoparticles for their enhancement of catalytic surface interaction, synergic effects, de-alloying effects activity and selectivity.154 155 171 172 In the case of Pt based (chemical and structural changes from alloy structures into multi-metal nanoparticles, this effect will be a synergic core–shell structures due to structure-phase separation of catalytic activity and sensitivity, leading multi-function nanoparticles in catalytic operation), unknown interesting effects of HOR and ORR These will be new and crucial effects in electro-catalysis In particular, the melting of topics of research directions of interest to scientists in fur139 core–shell structure was observed and discussed The ther investigations of Pt based catalysts or new catalysts formation of the thin Pt layers or the thin layers of Pt/noble without using Pt metal metals (Au, Ag, Ru, Rh, and Pd) around 1–10 nm are very important to researchers and scientists However, the unknown effects of the thin cheap metals layers (around 3.5.2 De-Alloying Effects 1–10 nm) on the Pt core (1–10 nm) are not intensively Recently, Pt–Ni, Pt–Co, and Pt–Cu catalysts have showed investigated.151 the high ORR activity at cathode in PEMFC The dealloying phenomena of Pt based bimetallic alloys with 3.4.3 Complex Nanostructures various structures are discovered, especially in Pt–Cu bimetallic nanoparticles In addition, the degradation of Pt Pt nanoparticles can be used in the hybrid catalysts and Pt based catalysts was studied in the operation of fuel with noble metals, cheap metals, and oxides hybrid cell for a long time This is due to the phenomena of disnanoparticles,152 153 for example, Pt–SiO2 –CeO2 , Pt–Fe2 O3 solution, aggregation, and clustering of the as-prepared Pt core–shell nanoparticles, Pt–SiO2 core–shell nanoparticles, 4814 J Nanosci Nanotechnol 13, 4799–4824, 2013 Long et al Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells nanoparticles, CO poisoning and other poisoning intermediates on the electrodes of PEMFC and DMFC.6 156–162 However, the catalytic properties of kinds of Pt based catalysts will be gradually changed in respective to the gradual changes of their nanostructures, from alloy to core–shell in the partial changes, and inversely, from core–shell to alloy in the partial changes J Nanosci Nanotechnol 13, 4799–4824, 2013 4815 REVIEW shells can be Pt, Pt–Au, Pt–Rh, Pt–Ru, and Pt–Pd etc The core–shell catalysts with the thin shells of Pt, Pt–noble metals give excellent ways of reducing the use of Pt metal in large amount The syntheses of nanosystems of bimetallic nanoparticles with high homogeneous size and morphology are the large challenges to scientists The electrochemical surface areas (ECA) were estimated by considering the area under the curve in the hydrogen desorption region of the forward scan and using 3.5.3 Janus Effects 0.21 mC/cm2 for the monolayer of hydrogen adsorbed on The core–shell bimetallic nanoparticles were changed in a Pt surface There are the specific regions in the cyclic to the various complex phases, so-called Janus chemical voltammogram (Fig 7) They show highly and good catconfiguration (Fig 6) or segregated structures to the case alytic activity and surface kinetics for the case of both of Cu–Ag core–shell nanoparticles but the TEM images of the Pt catalysts of 10 nm and the Pt–Pd core–shell catasmall nanoparticles were seen that could contribute to the lysts of 25 nm It is clear that the complete removal of formation of Janus structure in such one particle Thus, the PVP and high heat treatments of our catalyst preparation in role of small nanoparticles is crucial to the formation of H2 /N2 offer the good characterization of the size, surface, various structures of nanoparticle products.163 It is true that structure, and morphology Therefore, the highly long-term the phenomena of the clear separation of structural phases catalytic activity, stability, and durability in chemical and are found in alloy nanoparticles with various compositions physical Pt or Pd based catalysts are needed in the catalyst layers of next fuel cells, such as DMFCs and PEMFCs 3.5.4 Collision Effects Therefore, we can remove polyvinylpyrrolidone (PVP) or capping agents from the as-prepared Pt nanoparticles by Among the above effects, there is a new phenomenon, the simpler modified methods.170 which needs to be transparently clarified in detail It is In one interesting work, the solution of the core–shell interaction phenomena of the as-prepared nanoparticles nanostructure is one of the best choices of enhancing catthrough weak and strong collisions In various soluDelivered by Publishing Technology to:activity TWENTE UNIVERSITY alytic of nanoparticles with various structures The tions and solvents, the nanoparticles tend to exhibit their IP: 130.89.234.194 03 Junof2013 15:14:52 syntheses the pure Pt catalysts containing Pt nanopar136 On: Mon, This Scientific Publishers interactions through weak and strong collisions Copyright American ticles with the size range of 10 nm (4–8 nm) and Pt–Pd can lead to change their inherent characterization in the core–shell nanoparticles with the size range of 30 nm (15– 137 Janus nanostructures, especially various kinds of metal 25 nm) are discussed (Fig 7) We proved that the Pt–Pd nanoparticles Therefore, we can need to study Pt or Pd core–shell catalysts possess catalytic property much betbased nanoparticles in the further intensive investigations ter than Pt catalysts In particular, the Pt–Pd core–shell of catalytic activity and re-activity involving in the size, catalysts exhibited fast and highly stable catalytic activshape and morphological transformations in various soluity in the hydrogen catalytic activity The MOR activity tions, ion liquids, and solvents under high temperature was significantly enhanced by the Pt–Pd core–shell catand pressure conditions for long-term stability in the size alysts with the current density much higher than that of ranges from nano to micro in both experimental processes Pt catalyst Importantly, we showed that size effect in the and first principle computer simulations in catalysis as size limit range of 10 nm is not as important as the core– well as various observations and evidences of HRTEM shell nano-structuring effect in the size range of 30 nm measurements.164–168 A new phenomenon of the collision (15–25 nm) This led to conclude that the fast, stable, of the as-prepared Pt nanoparticles at the nano-scale of and sensitive hydrogen adsorption is very crucial for next 20 nm was also found in the evidences of high resolution fuel cells, such as PEMFC and DMFC In addition, the TEM images.136 issue CO poisoning was not observed in cyclic voltammetry (CV) measurements because of the good reduction of 3.6 Opportunities and Challenges weak and strong COad intermediates by the Pt and core– shell Pt–Pd catalysts The ORR of Pt catalyst observed An as-prepared catalyst included Pt–Pd alloy/mesoporous is more sluggish than that of Pt–Pd core–shell In this CNT microparticles, which showed the high catalytic case, the fast enhancement of ORR on the electrode of activities in the hydrogenation of allyl alcohol.169 the Pt–Pd core–shell catalyst is clearly observed in respecIn particular, the new Pt or Pt–Pd or Pt-noble metals based tive to their fast hydro adsorption/desorption These are the catalysts are of very interest because of reducing the high most advantages of the core–shell bimetallic nanoparticles cost of Pt rare and noble metal for FCs The thin shells Therefore, the Pt–Pd core–shell catalysts can significantly of Pt-noble metals on the thick cores of cheap base metincrease the HER, HOR, and ORR as well as ability of als, alloys, ceramics, glasses, oxides will be large research against CO poisoning The mechanism of reducing CO topics for nano-catalysis and various fuel cells Thus, the Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells Long et al (A) (C) (D) REVIEW (B) (E) (F) Delivered by Publishing Technology to: TWENTE UNIVERSITY IP: 130.89.234.194 On: Mon, 03 Jun 2013 15:14:52 Copyright American Scientific Publishers Fig (A) HRTEM images of Pt-Pd core-shell The thin Pd shells protect polyhedral Pt cores The nucleation and growth of Pd shells are controlled by a chemical synthesis Scale bars: (a)–(c) 20 nm (d) nm (e) nm (f) nm (B) Cyclic voltammogram of Pt nanocatalysts, and Pt-Pd core-shell nanocatalysts on glassy carbon electrode in N2 -bubbled 0.5 M H2 SO4 electrolyte (scan rate: 50 mV s-1) (C) Cyclic voltammograms towards methanol electro-oxidation of Pt nanocatalyst and Pt-Pd nanocatalyst (D) Chronoamperometry data of Pt and Pt-Pd nanoparticles Electrolyte solution of 0.5 M H2 SO4 + M CH3 OH and polarization potential about E = 0.5 V (E) Cyclic voltammograms of as-prepared Pt-Pd core-shell nanocatalysts in 0.5 M H2 SO4 in the ranges of E = −0.2 V to E = V and E = −0.2 V to E = V (F) Cyclic voltammograms of as-prepared Pt nanocatalysts in 0.5 M H2 SO4 in the ranges of E = −0.2 V to E = V and E = −0.2 V to E = V (G) Cyclic voltammograms of as-prepared Pt-Pd core–shell nanocatalysts in 0.5 M H2 SO4 in the ranges of E = −0.2 V to E = V and E = −0.2 V to E = V Reprinted with permission from [122], N V Long et al., Electrochim Acta 56, 9133 (2011) © 2011, Elsvier Publishers poisoning coverage occurred on the active sites of catalytic activity of the Pt and Pt–Pd core–shell catalyst due to a good catalyst preparation The mechanism of reducing CO poisoning coverage on Pt–Pd core–shell nanoparticles is known by the synergic effects of Pt based bimetallic 4816 nanoparticles between the core (Pt or Pd) and the shell (Pt or Pd), leading to that the Pt based core–shell bimetallic nanoparticles are the best Pt based nanostructures in electro-catalysis of hydrogen and methanol for PEMC and DMFC In the catalyst preparation, the as-prepared Pt, Pd, J Nanosci Nanotechnol 13, 4799–4824, 2013 Long et al Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells J Nanosci Nanotechnol 13, 4799–4824, 2013 4817 REVIEW of the as-prepared Pt–Pd catalysts proved the highest catand Pt–Pd nanoparticles were heated at about 300 C in alytic, selective, sensitive, and quick activity much better H2 /N2 , which offered the good characterization of the size, than the single, alloy and mixture of the as-prepared catasurface, structure, and morphology The effects of using lysts The Pt and Pd based core–shell catalysts in the range a suitable temperature range in heat treatment should be of 30 nm showed a good characterization, such as high suitable to various FCs, for example the better ORR activcurrent density, and against the CO poisoning much better ity This depends on the operating temperature of varithan various Pt, Pd, Pt–Pd, and Pd–Pd bimetallic catalysts ous FCs They were characterized by the chemical activity in the various forms of mono metal (Pt or Pd) nanoparoccurring at the electrode surface In the forward sweep, ticles, bimetallic nanoparticles with various structures of the first region assigned to hydrogen desorption is crualloy, core–shell, and mixture.171 172 122 123 In our works, cial to confirm catalytic activity of the Pt catalysts The we did not observed the CO stripping in all our electroslow kinetics of hydrogen desorption of the case of Pt chemical experiments because the good preparation procatalyst was confirmed in the cell before the stabilization cesses and heat treatments were used of CV was achieved from the first cycle to the twentiThey include Category eth cycle, and the fast kinetics of hydrogen desorption of (1) alloy nanoparticles with polyhedral, spherical, nearthe case of Pt–Pd core–shell catalyst Indeed, the results polyhedral, near-spherical shapes and morphologies of proved the good desorption and adsorption of hydrogen 10 nm (5–10 nm); Category of both Pt catalysts and Pt–Pd core–shell catalyst as evi(2) Mono-nanoparticles (Pt, Pd), bimetallic nanoparticles dences of good catalytic activity of two kinds of important (Pt–Pd) with polyhedral, spherical, near-polyhedral, nearcatalysts in the preparation process and heat treatment spherical shapes and morphologies of 10 nm (5–10 nm) To evaluate the catalytic activity of the prepared catalysts, for small nanoparticles, and, of 30 nm (20–30 nm) for ECSA of the Pt catalyst is calculated to be (10.5 m2 g−1 ) large nanoparticles; Category in a comparison with that of the Pt–Pd core–shell cata(3) Pt–Pd core–shell nanoparticles with good polyhedral lysts (27.7 m2 g−1 in our catalytic investigations Pt–Pd shapes and morphologies of 30 nm (15–25 nm); Category core–shell catalyst with stable and high catalytic activity (4) Pd–Pt core–shell nanoparticles with good spherical showed a very high initial current of j = 29 × 10−3 A or near-spherical shapes and morphologies of 20 nm cm−2 with 30.01% current left after h of polarization, (6–16 Category by Publishing Technology to: nm); TWENTE UNIVERSITY much higher than the Delivered Pt catalyst with the initial current (5)03Pt–Pd alloy and core–shell nanoparticles with large IP: 130.89.234.194 Jun 2013 15:14:52 of j = 33 × 10−4 A cm−2 with 3.67% current left On: after Mon, Copyright American Scientific Publishers and irregular shapes and morphologies of various ranges h of polarization Therefore, the most stable Pt–Pd core– of 10 nm, 20 nm, 30 nm, up to 40 nm; and Category shell catalyst (15 min) showed the highest initial current of (6) Pd–Pt alloy and core–shell nanoparticles with large about 29 × 10−3 A/cm2 or about × 10−3 A/cm2 with and irregular shapes and morphologies of 30 nm about 30% current left after h in its polarization.171 In our (15–30 nm) research, the elaborative heat treatments of the as-prepared Pt, Pd, Pt–Pd catalysts at about 300 C were used in order Importantly, the core–shell structures of Pt based bimetalto obtain the high catalytic activity and stability because lic nanoparticles show the most advantages of the abilthe treated nanoparticles possessed the very high hardness ity of enhancing catalytic activity and sensitivity in both of nanostructures However, the good characterization of the HER and/or HOR mechanisms and ORR and/or the as-preparation nanoparticles with their surface, strucMOR mechanisms (Fig 8) According to the Pt–Pd nanoture, size, shape, and morphology should be kept during structures with the forms of alloy, cluster and mixture, heat treatment at high temperature Thus, the Pt–Pd alloy the electrocatalytic properties were significantly enhanced and core–shell catalysts exhibited good activity and stawith the Pt–Pd bimetallic nanoparticles observed because bility in the desirable nanostructures after heat treatment of very strong synergic effect in well-shaped core– or sintering at 300 C This is necessary to enhance and shell morphologies and nanostructures.71–73 122 123 In our improve the catalytic activity, stability and durability of electrochemical data, Pt–Pd catalyst have various nanothe as-prepared nanoparticles.125 126 structures of Pt–Pd alloy, Pt–Pd cluster and mixture, According to our previous research, we also observed Pt–Pd core–shell (15 min), Pd–Pt core–shell, Pt–Pd core– that the Pt–Pd alloy and core–shell bimetallic nanopartishell, Pd–Pt core–shell, according to ECA (m2 /g) of 12.7, cles are simply synthesized (Fig 8) The epitaxial growth 11.5, 27.7, 17.7, 13.6, and 14.2 m2 /g, respectively They mode of the Pd-monolayers shells on the Pt nanocores can showed E(V) of 0.7, 0.67, 0.63, 0.65, 0.77, 0.73 V, respecbe controlled The Pt–Pd or Pd–Pd core–shell nanoparticles tively according to the current response The showed the with the controllable thin Pt or Pd nano-shells in the various peak current in the forward scan if or ifoward (A/cm2 forms of the monolayers exhibit their great electrocatalysis of × 10−3 , × 10−4 , × 10−3 , × 10−3 , × for direct methanol fuel cells (DMFCs) Interestingly, the 10−4 , × 10−3 A/cm2 , according to the current left after size issues in the catalytic activity are not as important as h in the polarization at 0.5 V, the current lelf about morphology and nanostructure The core–shell structures 29.40%, 38.70%, 30.00%, 23.80%, 23.80%, and 3.68%, Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells Long et al REVIEW (A) Delivered by Publishing Technology to: TWENTE UNIVERSITY IP: 130.89.234.194 On: Mon, 03 Jun 2013 15:14:52 Copyright American Scientific Publishers (B) (C) (D) Fig (A) (a)–(c) TEM and HRTEM images of Pt-Pd core-shell nanoparticles (Category 3) (d)–(i) TEM and HRTEM images of Pd-Pt coreshell nanoparticles (Category 4) (B) Cyclic voltammograms of Pt-Pd nanoparticles with their different configurations Electrolyte solution was 0.5 M H2 SO4 (Scan rate: 50 mV/s) (C) Cyclic voltammograms towards methanol electro-oxidation of Pt-Pd nanoparticles with their different configurations Electrolyte solution was 0.5 M H2 SO4 + M CH3 OH (Scan rate: 50 mV/s) (D) Chronoamperometry data of Pt-Pd nanoparticles with their different configurations Electrolyte solution is 0.5 M H2 SO4 + 1.0 M CH3 OH The polarization potential was 0.5 V Reprinted with permission from [123], N V Long et al., Int J Hydrogen Energy 36, 8478 (2011) © 2011, Elsvier Publishers respectively Among various Pt–Pd alloy, cluster and mixture, core–shell nanostructures, Pt–Pd core–shell catalyst with the most stable configuration showed highest value for ECA (27.7 m2 /g), with the highest initial current 29 × 10−3 A/cm2 (or × 10−3 A/cm2 for two experiments with about 30% current left only after h in its polarization.172 Most of the core–shell bimetallic nanoparticles showed that the Frank-van der Merwe (FM) and Stranski-Krastanov 4818 (SK) growth modes coexist in the nucleation, growth, and formation of the shells on the cores It is predicted that the FM growth becomes the main favorable growth compared with the SK growth in the formation of the thin shells of core–shell nanoparticles and nanostructures or the SK growth becomes the main favorable growth compared with the FM growth in the formation of the thin shells of core–shell nanoparticles and nanostructures In our research, we describes a strategy to improve the catJ Nanosci Nanotechnol 13, 4799–4824, 2013 Long et al Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells J Nanosci Nanotechnol 13, 4799–4824, 2013 4819 REVIEW nanoparticle products We need novel methods of removalytic activity of the Pt based catalysts through Pt and ing PVP polymer from the as-prepared PVP-Pt nanoparPd based alloy and core–shell nanoparticles In addition, ticles by chemical methods or others without high heat the Pd–Pt nanoparticles showed the high hydrogen soltreatment to retain the good characterization of size, shape ubility because of the co-existence of Pd(2 H), Pt(2 H), and morphology in the range of 10 nm (1–10 nm) The Pt/Pd(2 H) and Pt–Pd(2 H) hydride phases in the very tiny hardening of the pure Pt-nanoparticles catalyst is crucial to Pt–Pd nanoparticles This is the inherent property of Pd keep the good characterization of size, surface, shape, and and Pt metals.173 174 In this context, two Pt and Pd metals morphology We also need to use suitable solvent for keepshow a very high strong inherent interaction with hydroing the as-prepared metal nanoparticles for a long time in gen For example, at room temperature the Pd metal has the safety without any changes of their size, shape, moran unusual property of absorbing up to 900 times its own phology, surface, and structure because the characteristics volume of hydrogen Therefore, a crucial question to sciof Pt nanoclusters and nanoparticles in the size range of entists is how to explain the mechanisms of hydrogen 10 nm is the collapse of their various structures In particadsorption and desorption occurring on both the surface ular, the heat treatment processes should be used for hardand volume bulk of very tiny Pt nanoparticles We can use ening the pure Pt catalyst or the Pt based catalyst avoiding some percent of suitable metal atoms on the surface of the the collapse and self-breaking of the Pt nanostructures in as-prepared Pt nanoparticles for reducing CO poisoning the as-prepared nanoparticle catalysts In future, we can quickly The question is that hydrogen activity in fuel cells make the Pt nanoparticles of 10 nm (1–10 nm) or other occurring only on surface of the nanoparticles or in the metal nanoparticles with high surface roughness or high active catalytic sites of the volume bulk of the nanoparticoncave-convex surface for a better catalytic activity The cles through their specific hydride phases.175 In the DFT surface roughness is also durably hardened in the goals calculations according to model electrodes The Pt–Ru and of durability and stability of the pure Pt particle catalyst Pt–Sn alloys potentially show the good MOR In comparTherefore, the desirable structures of Pt nanoparticles can ison with Pt–Ru and Pt–Sn alloys, it is predicted that the be protected in its high hardening without self-breaking Pt–Cu alloys can be the promising anode catalysts in a structure phenomena In the case of high porosity of one common volcano plot.176 177 Pt nanostructure of 10 nm (1–10 nm), this characterization Specifically, there are no exact confirmations and eviDelivered Publishing Technology needto:toTWENTE be retainedUNIVERSITY and kept for a long time for durabildences of the lowest amount of Pt by metal used for various IP: 130.89.234.194 On: Mon, 2013The 15:14:52 ity03 andJun stability concepts of the nanosized ranges of fuel cells, such as DMFCs and PEMFCs for the longCopyright American Publishers 10 nm…1000 nm…10 m can be used for the ability of term stability and durability of Pt based catalysts as well Scientific catalytic activity of the pure catalysts Finally, all of asas here, the stabilization of Pt based catalyst in various prepared catalytic nanoparticles need very high dispersion fuel cells with the lowest weight of Pt loading We sugand distribution on the supports in the catalyst layer for the gest that the modifications are proposed in mixing the ashighest homogeneous nanosystems The shape of Pt and prepared nanoparticles, including Pt and Au nanoparticles, Au nanoparticles supported on TiO2 (110) was studied via and so on to make novel Pt catalysts Certainly, a new mixing method (various nanoparticles for new catalysts) inverse micelle encapsulation The fast cooling from very is of extreme importance Because precious metal Pt is high temperature is a very excellent method for keeping limited, and very expensive, this is a big challenge that the shapes and morphologies of nanoparticles in future new FC technology must overcome on using cheaper catBy this way, the ordered arrays of well-separated threealysts using base metals and alloys that have the same dimensional faceted nanoparticles were formed in their properties as the pure Pt catalyst The metal nanoparticles equilibrium state.178 of chemical elements exhibiting the HOR reactions can A lot of attempts were also made to synthesize Pt/C be used to replace Pt metal despite of the fact that they catalysts The influence of carbon based supports and the have catalytic activity and sensitivity much smaller than role of synthesis procedures on the formation of Pt and Pt metal It is certain that next fuel cell technologies can Pt–Ru clusters and nanoparticles for the development of be realized in large-scale commercialization for sustainhighly active fuel cell catalysts.179 Pt decorated PdAu/C able energy, such as small mobile devices The ways of catalysts with ultralow Pt loading can be used for formic removing PVP, CTAB, polymer, and other capping agents acid electrooxidation.180 Indeed, size-controlled synthesis protecting Pt nanoparticles are also very important to the of Pt nanoparticles and their electrochemical activities pure catalysts The best ways are simple chemical methods were focused on the improvement of ORR.181 for all the as-prepared particles dropping at the bottoms of The recent development of the new catalysts without the containers We simply pour the solutions of PVP and the use of Pt metal for the ORR has become one of most other solvents to obtain the nanoparticles at the bottoms of important roles of large-scale commercialization of varithe containers without the necessity of using centrifugaous fuel cells The base metals can be used for new cattion processes and expensive centrifuges These chemical alysts as Ni, Co, Fe, Cu, Mn, Cr, W, Sb, Mo etc.182 183 methods will be new methods for obtaining the as-prepared Recently, Pt–Fe, Pt–Co, Pt–Ni, Pt–Cu, and Pt–M/C (M: V, REVIEW Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells Long et al Ni, Cr, Co, and Fe) based nanoparticles show promis4 APPLICATIONS ing catalysts for PEMFC and DMFC because of high So far, Pt metal catalyst or Pt/noble metal (Au, Ag, Pd, Rh, catalytic activity.184–186 In various research predictions in Ru, Ir, Os) based nanoparticles with novel nanostructures catalysis, biology and medicine, Pt and Pd metal can offer for next fuel cells have been synthesized by various simple potential applications in green nano-catalysis in the forms physical and chemical methods Similarly, Pt-cheap metal of alloy and core–shell structures, especially Pt and Pd (Cu, Fe, Ni, Co) nanoparticles have been successfully syn187 188 shell/oxide core for green energy applications Apart thesized These prove that large-scale commercialization from the development of proton-conducting membrane, of fuel cells, such as low-temperature DMFC and PEMFC catalytic layers, gas-diffusion layers, and the anodic and can be realized in near future with their low costs Novel Pt cathodic bipolar plates, new catalysts with high catalytic and Pd catalysts need to be intensively studied for achievactivity and sensitivity need to be prepared and improved ing the high durability, stability, reproducibility, and safety in the good Pt catalyst of 10 nm, 20 nm, 30 nm for large for long-term applications Thus, we emphasize their propquantum-size effects, new Pt based alloys (10 nm, 20 nm, erties of crystal structure, size, morphology, shape, and 30 nm), Pt and metals core–shell catalysts (10 nm, 20 nm, composition under control, which can be used in homo30 nm), new Pt based mixture catalysts (Pt nanoparticles, geneous and heterogeneous nano-catalysis and fuel cells bimetal, multimetal, oxide, glass, ceramics), new catalysts The designing of novel alloy and core–shell nanopartiwithout the use of Pt metal The new supports need to be cles with high performance for catalysis and FCs are very developed for reducing CO poisoning At present, tungsten neccessary The research results of Pt–Pd alloy and core– monocarbide materials (WC) and the Pt skin-WC catalyst shell catalysts were showed in the core–shell structures in showed the catalytic activity as the same as Pt metal.189 190 the highest catalytic activity with the advantages of the Therefore, Pt monolayer based WC, Pt monolayer/Wx C, thin shells in the range of 10 nm A concept of catalytic and Pt monolayer/transition metal carbides (TMC), and ranges in nano-catalysis is introduced, such as the impormixture catalyst of base metals and TMCs potentially offer tant ranges of 10 nm, 20 nm, 30 nm etc for the pure low-cost electrocatalysts in DMFC and PEMFC In further Pt catalyst, the Pt base bimetallic catalyst and various Pt development of PEMFCs and DMFCs, the most challenges based alloy and core–shell catalyst However, the big chalof new catalysts with or without the use of Pt are the lenges for making novel Pt and Pd based alloy and core– Publishing Technology to:catalysts TWENTE controlled synthesis of Delivered bimetal andby multi-metal core–shell shell withUNIVERSITY the thin Pt or Pt-noble metal shells IP: 130.89.234.194 On: Mon, 03 Jun 2013 15:14:52 nanoparticles in the certain nanosized ranges for nanoare considered in low-temperature PEMFCs and DMFCs American Publishers catalysis, energy conversion, and fuelCopyright cells In addition, the Scientific In addition, the highly long-term durability and stability new mixture nanoparticles (base metals, oxides, glasses, of Pt and Pd based catalysts showed the importance in the and ceramics) will be intensively studied in nano-catalysis large-scale commercialization of FCs technologies, PEMand energy conversion in order to possibly replace the FCs and DMFCs The development of Pt and Pd based Pt metal.152 153 191 192 CeO2 –Pt–SiO2 structure showed a core–shell nanoparticles for catalysts engineering with the new heterogeneous catalyst system for the reaction of best catalytic activity, durability, and stability are very crumethanol and ethylene In catalytic activity, Pt/carbon supcial The very large size-quantum effects of Pt and Pd ports also showed the instability in low temperatuture based core–shell catalysts at the ranges of around 1–30 nm fuel cells because of the dissolution of Pt nanoparticles are of importance in homogeneous and heterogeneous at high voltages.193 In a simple way, Pt–Fe2 O3 core–shell catalysis It is certain that Pt catalyst show the largest surnanoparticles were successfully synthesized.194 Pt nanoparface in electro-catalysis area in the nanosized range of ticles of 1–2 nm and 5–6 nm can be integrated inside 10 nm for potential FC applications Moreover, we protubular TiO2 nanomaterials.195 FePt3 /CoFe2 O4 core/shell pose that the homogeneity of the as-prepared Pt nanoparnanostructures.196 Thus, the new Pt nanoparticles with varticles supported on various supports will lead to obtain ious core–shell, hollow, and multi-branch structures are the excellent characterizations of surface structure, interthe candidates for further investigation of nano-catalysis nal structure, shape and morphology in the well-nanosized In addition, Pt and Pd based catalysts with the many thin ranges of 1–30 nm are of importance in homogeneous shells of several nm can be developed for the goals of new and heterogeneous catalysis In addition, a concept of the catalysts in fuel cells The new catalysts can be created standard Pt catalyst of about 10 nm can be commonly by complex colloidal assembly but homogeneous and hetemployed for a comparison with any new Pt based cataerogeneous nanocrystals will show the complex catalytic lysts for the next developments and large-scale commerproperties These are new ways of developing the new cialization of PEMFCs and DMFCs of high efficiency The catalysts in nano-catalysis Novel homogeneous catalytic long-term reliability and stability of PEMFC and DMFC nanosystems of the core–shell nanoparticles and nanounder higher temperature and other conditions at continstructures with the thin shells of noble nanoparticles or uous operations need to be further studied To reduce the new alloys or mixtures provide research directions of next usage of Pt on the electrodes, new catalysts need to be fuel cells developed in the cathode with using cheap metal/oxide 4820 J Nanosci Nanotechnol 13, 4799–4824, 2013 Long et al Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells mixtures but mass production avoiding the dependency on Pt catalyst of high cost Promising practical applications of PEMFC and DMFC for our lives will be fuel cell vehicle, automobiles, mobile devices, home or household appliances, and even stationary fuel cell system STABILITY AND DURABILITY or near-sphere have the high durability and ability according to other forms of shapes and morphologies However, they need to be durably hardened before the use avoiding the collapse of the as-prepared Pt structures with good size, shape, and morphology A concept of the standard Pt catalyst is proposed for the polyhedral Pt nanoparticles of 10 nm In one particle, even less than 10 nm or more than 1000 nm, the structural and morphological variations can occur at atomic scale The separation of structural phase also can occur This is very crucial to understand nanocatalysis In addition, the utilizations of low Pt loading catalysts are proposed in the core–shell catalysts with the thin shells of Pt, Pd, Pt–Pd, and various noble metals J Nanosci Nanotechnol 13, 4799–4824, 2013 4821 REVIEW In fuel cell testing, researchers proved that the Pt mass activity of two commercial Pt/C catalysts is about three times smaller than that of the PtML –Pd/C electrocatalyst in order to understand the stability and durability of Pt–Pd catalyst of Pt monolayers (PtML or the thin Pt skin layer After 60,000 potential cycles, Pt/C with the use of the Pt loading of 0.133 mg cm−2 had lost almost 70% of its activity, CONCLUSIONS compared with < 20% for PtML –Pd/C with the use of the Pt loading of 0.085 mg cm−2 , and the activity of Pt/Ketjen In this review, we have presented the newest highlights of black carbon with the use of the Pt loading of 0.3 mg cm−2 the controlled synthesis of Pt metal nanoparticles in nanohad fallen > 40% after only 10,000 cycles In particular, the catalysis by chemical method The paramount issues of Pt mass activity of PtML –Pd/C catalyst increased from the controlling size, shape, structure, composition of the Pt and initial threefold to fivefold enhancement over that of Pt/C Pd based nanoparticles have been intensively presented after 60,000 cycles showing superior stability of the PtML – The catalytic activity and sensitivity of metal nanopartiPd/C due to the synergic core–shell effect In addition, the cles, such as Pt, Pd, Ru, Rh, Au, Ag, and so on are the research results and key evidences of the successful uses highest activity and sensitivity in the size limit range of of the low Pt loading in various Pt based catalysts were 10 nm, 20 nm and 30 nm because of the consequence 197 presented The high and long-term stability and durabilof large quantum-size effect Thus, metal, bimetal, and ity of Pt-skin or Pt-monolayer skin based catalysts were Delivered by Publishing Technology to: TWENTE UNIVERSITY muli-metal nanoparticles with various structures of sin197–200 firmly confirmed in various interesting works The Mon, IP: 130.89.234.194 On: 03alloy, Jun 2013 15:14:52 gle, core–shell, mixture, hybrid, and so on, with core–shell nanocatalysts show the most advantages to the Scientific Publishers Copyright American or without the uses of noble Pt or Pd metals will offer PEMFC and DMFCl commercialization excellent opportunities in nano-catalysis, energy converThe Pt shell can be designed with the thickness of sevsion, and next fuel cells as well as biology, medicine, and eral nm.171 172 In the reduction of CO poisoning, Pt/M nanomedicine Through chemical and physical methods, catalysts with core–shell (M = Ru, Rh, Ir, Pd, Au) were nanoparticles with new textures and structures for green studied with the CO coverage The shell is the coatnano-catalysis can be successfully fabricated In particular, ing of Pt thin layer The CO poisoning for Pt–M catacore–shell hybrid nanostructures between metals, alloys, lysts in the hydrogen-rich environments on these surfaces oxides, glasses, and ceramics are of very importance and showed the following order in Ru/Pt < Rh/Pt < Ir/Pt < interest to scientists and researchers in nano-catalysis as Pd/Pt < Pt < Au/Pt due to the composition effect The well as various sciences and technologies Our critical Pt/Ru based catalyst showed the highest catalytic activity review proves that next fuel cells, such as PEMFC and because of the weakest CO binding on the surfaces of Pt/Ru DMFC will deal with the issues and challenges of energy catalyst.201 In another work, importantly the Pt–Pd/C catcrisis on the basic of developing new nano-catalysts, even alyst showed a better durability than Pt/C,202 and Pt46 Pd54 203 without relying on the use of expensive and noble platwith high catalytic activity The extended X-ray absorpinum metal in the anodes and cathodes, especially in the tion fine-structure spectroscopy was used to study bimetalcathodes in respective to the ORR lic nanoparticle catalysts The calculations showed that the core–shell bimetallic nanoparticles are the most chalAcknowledgments: This work was supported by lenges of the controlled synthesis of core–shell bimetalNAFOSTED Grant No 104.03-2011.33, 2011 This work lic nanoparticles but the most advanteges of durability and was supported by Laboratory for nanotechnology, Ho-Chistability.204 Among the classes of engineered core–shell Minh Vietnam National University, Ho-Chi-Minh, Vietnanoparticles, bimetallic core–shell nanoparticles are one nam This work was supported by Kyushu University, of the most important classes in pratical application in Japan We greatly thank Research and Education Cencommunications, catalysis, biology and medicine.205 In our ter of Carbon Resources, GCOE program, Kyushu Uniideas, we certainly confirm that the as-prepared Pt nanoparversity and Nagoya Institute of Technology for giving us ticles of 10 nm (1–10) nm, 20 nm (1–20 nm), and 30 nm (1–30 nm) with uniform shapes and morphologies, such significantly financial assistance in the program of science tetrahedra, cube, octahedra, and polyhedra as well as sphere and nanotechnology in Japan This work was supported by Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells Long et al REVIEW Structural 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Thus, the Platinum and Palladium Nano-Structured Catalysts for Polymer Electrolyte Fuel Cells and Direct Methanol Fuel Cells Long et al... 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