Synthesis and characterization of m doped tio2 (m=w, ir) materials as supports for platinum nanoparticles to improve catalytic activity and durability in fuel cells

VIETNAM NATIONAL UNIVERSITY - HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY TAI THIEN HUYNH SYNTHESIS AND CHARACTERIZATION OF M-DOPED TIO2 (M=W, Ir) MATERIALS AS SUPPORTS FOR PLATINUM NANOPARTICLES TO IMPROVE CATALYTIC ACTIVITY AND DURABILITY IN FUEL CELLS DOCTORAL DISSERTATION HO CHI MINH CITY, 2020 VIETNAM NATIONAL UNIVERSITY - HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY TAI THIEN HUYNH SYNTHESIS AND CHARACTERIZATION OF M-DOPED TIO2 (M=W, Ir) MATERIALS AS SUPPORTS FOR PLATINUM NANOPARTICLES TO IMPROVE CATALYTIC ACTIVITY AND DURABILITY IN FUEL CELLS Major subject: Chemical Engineering Major subject code: 62520301 Advisor: ASSOC PROF VAN THI THANH HO DR SON TRUONG NGUYEN i PLEDGE I pledge that this dissertation is my own research under the direction of the Assoc Prof Van Thi Thanh Ho and Dr Son Truong Nguyen The research results and conclusions in this dissertation are honest, and not copied from any one source and in any form The reference to the sources of documents (if any) has been cited and the reference sources are recorded as prescribed Signature Tai Thien Huynh ii ABSTRACT Low-temperature fuel cell systems have been drastically gaining attention because of their high energy production efficiency and near-zero emissions that can solve the serious reliance on fossil fuel In fuel cell technology, electrocatalysts play an important role at anode electrode and cathode electrode which directly impact the fuel cell performance Nowadays, carbon-supported Platinum catalysts are widely utilized in fuel cell technologies, however, they exhibit some restrictions; namely, poor durability due to the corroded carbon leading to sintering/detachment and agglomeration of Pt nanocatalysts, sluggish kinetics of fuel anodic oxidation and oxygen reduction reaction (ORR), CO poisoning of active sites of platinum nanocatalyst at even low CO concentration (< ppm) causing significant performance deterioration in the long-term operating condition of fuel cells Up to now, developing robust electrocatalysts is still a major challenge for further commercialization of fuel cell technologies One of the most effective approaches to solve these problems is to use non-carbon materials, which have emerged as promising alternative catalyst supports due to the superior corrosion resistance in electrochemical media and strong interaction with Pt nanocatalysts and therefore, the electrocatalytic activity and stability of Pt-based catalysts can be significantly enhanced Among carbon-free supports, titanium dioxide (TiO2) material has gained considerable attention in fuel cell application owing to superior electrochemical stability, non-toxicity and affordability Furthermore, the strong metal-support interaction (so-called ―SMSI‖) between TiO2 support and Pt nanocatalyst is a synergistic effect resulting in the significant enhancement of both electrocatalytic activity and durability of this electrocatalyst The intrinsic low electrical conductivity of TiO2, however, is a major hindrance to be solved for its further application in fuel cell technologies Recently, doping strategy of titania with transition metals has come to be known as the best way to enhance both the electronic conductivity of TiO2 and electrochemical activity and durability of Pt-based catalysts for fuel cell application iii To this end, I introduce the combination between Platinum nanocatalysts and M-doped TiO2 (M=W, Ir) supports, which were successfully synthesized by means of one-pot synthesis without surfactants/stabilizers or further heat treatment, to assemble robust 20 wt % Pt/Ti0.7M0.3O2 (M=W, Ir) catalysts for the methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) Experimental results demonstrated that 20 wt % Pt/M-doped TiO2 (M=W, Ir) electrocatalysts are promising anodic and cathodic electrocatalysts for low-temperature fuel cells In this work, a novel Pt catalyst supported on mesoporous Ti0.7W0.3O2, which exhibited high conductivity (2.2x10-2 S.cm-1) and large specific surface area (201.481 m2.g-1), was prepared successfully via rapid microwave-assisted polyol route It is found that uniform nm spherical-like Pt of nano-form adhered homogeneously on the surface of Ti0.7W0.3O2 Intriguingly, the electrochemical surface area of the 20 wt % Pt/Ti0.7W0.3O2 was found to be ~90 m2.g-1Pt, which is profoundly higher than that of the commercial 20 wt % Pt/C (E-TEK) catalyst For MOR, the If/Ib ratio of the 20 wt % Pt/Ti0.7W0.3O2 catalyst was found to be approximately 2.33, which is 2.5-fold higher than that of the commercial 20 wt % Pt/C (E-TEK) catalyst Similarly, the chronoamperometry data also revealed that the 20 wt % Pt/Ti0.7W0.3O2 catalyst possessed higher durability than the 20 wt % Pt/C (E-TEK) catalyst These aforementioned results indicated the much higher catalytic activity and better COpoisoning tolerance toward MOR of the 20 wt % Pt/Ti0.7W0.3O2 electrocatalyst which could be due to the strong interaction (SMSI) between Pt and M-doped TiO2 support leading to the weak adsorption of carbonaceous species on the active sites of Pt and thus increasing the catalyst’s activity and stability for the MOR in the direct methanol fuel cell For the first time, novel Ti0.7Ir0.3O2 support was prepared by means of a one-pot hydrothermal route as a catalyst support for Pt nanocatalysts to assemble robust electrocatalyst for both anodic and cathodic catalysts in low-temperature fuel cells For starter, the electrochemical surface area (ECSA) of the 20 wt % Pt/Ti0.7Ir0.3O2 nanoparticles (NPs) catalyst was found to be ~96.98 m2.g-1Pt, which is higher the 20 wt % Pt/C (E-TEK) catalyst For MOR, the superior catalytic activity and CO tolerance of the 20 wt % Pt/Ti0.7Ir0.3O2 electrocatalyst compared to the 20 wt % Pt/C iv (E-TEK) catalyst was demonstrated through the negative shift of 0.3 V, ~1.5-fold higher oxidation current density and ~1.87-fold higher If/Ib ratio of the 20 wt % Pt/C (E-TEK) catalyst For ORR, the 20 wt % Pt/Ti0.7Ir0.3O2 NPs electrocatalyst exhibited the good onset potential, which was positively shifted ~90 mV, and high electrocatalytic stability after 5000 cycling test compared to that of the 20 wt % Pt/C (E-TEK) catalyst Besides, ―electronic transfer mechanism‖, which does not appear in the conventional Pt/C catalyst, was founded in 20 wt % Pt/Ti0.7Ir0.3O2 NPs catalyst that could interpret for these enhancements of the robust Pt/Ti0.7Ir0.3O2 NPs catalyst Interestingly, even with low iridium doping concentration, the Ti0.9Ir0.1O2 support possessed a high electronic conductivity of 1.6x10-2 S.cm-1, which was ~105 times as high as pure TiO2 (1.37x10-7 S.cm-1), suggesting the efficient doping of iridium into TiO2 lattice The modified chemical reduction route utilized to fabricate the 20 wt % Pt/Ti0.9Ir0.1O2 electrocatalyst exhibited the good anchoring and uniform distribution of Pt nanoparticles (~3 nm) over Ti0.9Ir0.1O2 surface and thus eventually resulting in the high electrochemical surface area (~85 m2.g-1Pt) compared to that of the 20 wt % Pt/C (E-TEK) catalyst (~70 m2.g-1Pt) The cyclic voltammetry results in the methanol media revealed that the 20 wt % Pt/Ti0.9Ir0.1O2 exhibited superior electrocatalytic activity compared to the 20 wt % Pt/C (E-TEK) catalyst For instance, the 20 wt % Pt/Ti0.9Ir0.1O2 catalyst possessed a higher oxidation current density (~28.8 mA/cm2), a lower onset potential (~0.12 V) and a higher If/Ib ratio in comparison with the commercial 20 wt % Pt/C (E-TEK) catalyst It is worth noting that the chronoamperometry results also indicated that the 20 wt % Pt/Ti0.9Ir0.1O2 exhibited higher durability than the commercial 20 wt % Pt/C (E-TEK) catalyst This effective approach contributes to designing other advanced catalysts to revise conventional catalysts in low-temperature fuel cells v ACKNOWLEDGEMENTS First of all, I would like to express my deepest gratitude to my advisors, Assoc Prof Dr Van Thi Thanh Ho and Dr Son Truong Nguyen for suggesting the problem, supervising the work and being a potential source of inspiration at each stage of this dissertation research work I would like to express my deepest gratitude to Prof Nam Thanh Son Phan supported me during this dissertation research work at the HCMUT I would like to give deep thanks to Mr Hau Quoc Pham for the collaboration during years of working together The enthusiasm and generous support of him is highly appreciated I would like to express my gratitude towards my students, Mr At Van Nguyen, Ms Vi Thi Thuy Phan and Ms Anh Ngoc Tram Mai for their consistent support in this research Without them, the research process will not be as smooth and I also appreciate their valuable supports as well as help in achieving the results presented in this dissertation I would like to thank the Faculty of Chemical Engineering - HCMUT, the MANAR Laboratory - Faculty of Chemical Engineering – HCMUT, the Physical Chemistry Laboratory – HCMUNRE, the Applied Physical Chemistry Laboratory – HCMUS and the Key Laboratory of Polymer and Composite Materials – HCMUT for their support during the research period My special thanks to my parents, my wife and my children for their love, understanding, encouragement and consistent support throughout my dissertation journey Without their enthusiastic support, I could not complete my research Finally, I acknowledge The Young Innovative Science and Technology Incubation Program, managed by Youth Promotion Science and Technology Center, Hochiminh Communist Youth Union, HCMC, Vietnam (Project No 17/2017/HĐKHCN-VƯ and Project No 10/2018/HĐ-KHCN-VƯ) for financial support vi TABLE OF CONTENTS PLEDGE ii ABSTRACT iii ACKNOWLEDGEMENTS vi TABLE OF CONTENTS vii LIST OF TABLES xi LIST OF FIGURES .xii LIST OF SYMBOLS AND ABBREVIATIONS xix THE MOTIVATION OF RESEARCH CHAPTER INTRODUCTION AND LITERATURE REVIEW 1.1 Fuel cell systems 1.1.1 Overview of fuel cell technologies 1.1.2 Proton Exchange Membrane Fuel Cell 1.1.3 Direct Methanol Fuel Cell 12 1.1.4 Challenges and current issues of fuel cell systems 15 1.2 Non-carbon support materials .17 1.2.1 Tungsten trioxide (WO3) material 18 1.2.2 Iridium dioxide (IrO2) material 20 1.2.3 Titanium dioxide (TiO2) material 20 1.2.4 Metal-doped TiO2 materials 23 1.3 W-doped TiO2 material .26 1.4 Ir-doped TiO2 material 27 1.5 Methods for synthesizing M-doped TiO2 materials 28 vii 1.5.1 Sol-gel method 28 1.5.2 Hydrothermal method 28 1.5.3 Solvothermal method 29 1.5.4 Other methods 30 1.6 Methods for preparing Pt-based catalyst .30 1.6.1 Polyol method 30 1.6.2 Chemical reduction method 30 1.7 Objectives of thesis research .31 CHAPTER MATERIALS AND EXPERIMENT 34 2.1 Materials 34 2.2 Experimental procedure 34 2.2.1 Synthesis of W-doped TiO2 35 2.2.2 Synthesis of 20 wt % Pt/Ti0.7W0.3O2 catalyst 36 2.2.3 Synthesis of Ir-doped TiO2 38 2.2.4 Synthesis of Pt/Ti0.7Ir0.3O2 catalyst 40 2.3 Characterization techniques 41 2.3.1 X-ray diffraction (XRD) 41 2.3.2 X-ray photoelectron spectroscopy (XPS) 41 2.3.3 Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) 42 2.3.4 Transmission electron microscopy (TEM) and High-resolution transmission electron microscopy (HR-TEM) 43 2.3.5 Brunauer Emmett Teller (BET) surface area analysis 43 2.3.6 Electrical conductivity measurements 43 2.3.7 Electrode preparation and electrochemical measurements 44 viii 2.3.8 Electrochemical characterization techniques 47 CHAPTER HIGH CONDUCTIVITY AND SURFACE AREA OF Ti0.7W0.3O2 NANOSTRUCTURE SUPPORT FOR Pt NANOPARTICLES TOWARD ENHANCED METHANOL OXIDATION IN DMFC 53 3.1 Synthesis of Ti0.7W0.3O2 support 53 3.1.1 Effect of reaction temperature on W-doped TiO2 53 3.1.2 Effect of reaction time on W-doped TiO2 55 3.2 Characterization of the novel Ti0.7W0.3O2 support (optimum condition at 200oC for 10 hours) 60 3.2.1 The structure of Ti0.7W0.3O2 and un-doped TiO2 60 3.2.2 X-ray photoelectron spectroscopy (XPS) of Ti0.7W0.3O2 60 3.2.3 The morphology of Ti0.7W0.3O2 and un-doped TiO2 61 3.2.4 Elemental composition of Ti0.7W0.3O2 62 3.2.5 BET surface area of the Ti0.7W0.3O2 63 3.2.6 The electronic conductivity of the Ti0.7W0.3O2 65 3.3 Synthesis of the 20 wt % Pt/Ti0.7W0.3O2 catalyst 66 3.4 Electrochemical properties of the 20 wt % Pt/Ti0.7W0.3O2 catalyst 69 3.5 Conclusion 74 CHAPTER NEW Ir DOPED TiO2 NANOSTRUCTURE SUPPORT FOR PLATINUM: ENHANCING CATALYTIC ACTIVITY AND DURABILITY FOR FUEL CELLS 75 4.1 Synthesis of the Ti0.7Ir0.3O2 support 75 4.1.1 Effect of reaction time on Ir-doped TiO2 75 4.1.2 Effect of reaction temperature on Ir-doped TiO2 78 4.1.3 Effect of pH value on Ir-doped TiO2 80 ix Appendix DA plot of Ti0.7W0.3O2 at 200oC, 10h 146 Appendix BET of Ti0.7W0.3O2 at 220oC, 4h 147 Appendix BET of Ti0.7W0.3O2 at 220oC, 6h 148 Appendix BET of Ti0.7Ir0.3O2 at 210oC, 8h, pH=1 149 Appendix BET of Ti0.7Ir0.3O2 at 210oC, 8h, pH=2 150 Appendix XPS of Ti0.7Ir0.3O2 151 Appendix Curve fitting example of Ti0.7Ir0.3O2 152 Appendix XPS of the 20 wt % Pt/Ti0.7Ir0.3O2 153 Appendix 10 Curve fitting of the 20 wt % Pt/Ti0.7Ir0.3O2 Appendix 11 XPS of the Ti0.7Ir0.3O2 and 20 wt % Pt/Ti0.7Ir0.3O2 154 Appendix 12: XPS of the 20 wt % Pt/Ti0.7W0.3O2 155 Appendix 13 XRF of Ti0.7W0.3O2 156 Appendix 14 EDX of Ti0.7W0.3O2 157 Appendix 15 XRF of Ti0.7Ir0.3O2 158 Appendix 16 XRF of Ti0.9Ir0.1O2 159 Appendix 17 Cyclic voltammograms of (a) Ti0.7Ir0.3O2 NPs, (b) Ti0.9Ir0.1O2 and (c) Vulcan XC-72 supports after scanning cycle and 2000 scanning cycles recorded in nitrogen-saturated 0.5 M H2SO4 at a scan rate of 50 mV/s 160 ... characterization of M- doped TiO2 (M= W, Ir) materials as supports for platinum nanoparticles to improve catalytic activity and durability in fuel cells? ?? 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