electrocatalytic and fuel processing studies for portable fuel cells

ELECTRO CATALYTIC AND FUEL PROCESSING STUDIES FOR PORTABLE FUEL CELLS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University , , II ' By Paul H Matter, B.S **** The Ohio State University 2006 Dissertation Committee: Professor Umit S Ozkan, Adviser Professor Sheldon G Shore Professor W.S Winston Ho Approved by ?!I~J!~ Adviser Chemical Engineering Graduate Program UMI Number: 3220993 UMI Microform 3220993 Copyright 2006 by ProQuest Information and Learning Company All rights reserved This microform edition is protected against unauthorized copying under Title 17, United States Code ProQuest Information and Learning Company 300 North Zeeb Road P.O Box 1346 Ann Arbor, MI 48106-1346 ABSTRACT In the field of catalysis, the development of alternative catalysts for the oxygen reduction reaction (ORR) in Polymer Electrolyte Membrane Fuel Cell (PEMFC) cathodes has been an ongoing task for researchers over the past two decades PEM fuel cells are considered to be potential replacements for internal combustion engines in automobiles, and their reduced emissions and better efficiency would have huge payoffs for our environment, and in reducing our nation’s dependence on foreign oil To date, PEMFC cathode over-potentials are still significant, and the only materials discovered to be highly active and stable catalysts in an acidic environment are platinum-based Despite several major advances in recent years in reducing platinum loading in fuel cell electrodes, the high expense and low availability of platinum will hinder the large-scale commercialization of PEM fuel cells The most hopeful advances being made in replacing platinum are related to pyrolyzed organic macrocycles with transition metal centers (such as Fe or Co porphyrins and phthalocyanines) Encouragingly, it has recently been discovered that active electrodes could be prepared by heat-treating metal and nitrogen precursors (not necessarily organic macrocycles) together in the presence of a carbon support ii In the first study of this dissertation, catalysts for the Oxygen Reduction Reaction (ORR) were prepared by the pyrolysis of acetonitrile over various supports The supports used included Vulcan Carbon, high purity alumina, silica, magnesia, and these same supports impregnated with Fe, Co, or Ni in the form of acetate salt The catalysts were characterized by BET surface area analysis, BJH Pore Size Distribution (PSD), conductivity testing, Transmission Electron Microscopy (TEM), Temperature Programmed Oxidation (TPO), Thermo-Gravimetric Analysis (TGA), X-Ray Diffraction (XRD), X-ray Photo-electron Spectroscopy (XPS), Mössbauer Spectroscopy, Rotating Disk Electrode (RDE) half cell testing, and full PEMFC testing The most active catalysts were formed when Fe was added to the support before the pyrolysis; however, samples in which no metal was added still showed elevated activity for oxygen reduction The alumina-based samples showed the best activity, although they were less conductive, even after exposed alumina was dissolved away with hydrofluoric acid Within a support family, the more active catalysts had a higher amount of pyridinic nitrogen, as determined from XPS A theory has been proposed to explain this trend based on the formation of different nano-structures depending on which support material is used for the acetonitrile decomposition According to this theory, nitrogen-containing carbon samples with nano-structures that result in more edge planes being exposed (the plane in which all pyridinic nitrogen is found) will be more active for the ORR Recommendations for further research in this area are presented In volume II of this dissertation, Cu-based catalysts for hydrogen production from methanol and water were studied These catalysts have applications for mobile fuel cells that rely on hydrogen production from easier to store liquid fuels, such as methanol iii ACKNOWLEDGMENTS I acknowledge the support of my fellow HCRG group members, who were always willing to unselfishly help out in strenuous times I am specifically grateful to undergraduate researchers Ling Zhang, whose energy helped get this project started; Eugenia Wang, who helped expand on the array of available nano-materials for testing; and Maria Arias who helped with the large amount of electrochemical testing Furthermore, I am grateful to graduate students John Kuhn, who helped with collection of Raman spectra; and Elizabeth Biddinger, who helped with electrochemical testing I acknowledge the financial assistance and many unique learning opportunities from the NSF, and the NSF-IGERT program I acknowledge my adviser, Umit S Ozkan, for her support in my pursuit of a research area that is of deep interest to myself Finally, I acknowledge my family and friends who still love me even though I often put the work in the following pages ahead of their requests understanding, it definitely would not have been possible iv Without their VITA May 20, 1979 …………………………… Born – New Philadelphia, Ohio Summer, 2000 …………………………… Intern, NexTech Materials, Worthington, Ohio December 7, 2001 ………………………… B.S Chemical Engineering, The Ohio State University 2001 – present …………………………… Researcher and Graduate Fellow, The Ohio State University PUBLICATIONS Research Publications: Matter, P.H., Braden, D.J., Ozkan, U.S., "Steam reforming of methanol to H2 over nonreduced Zr-containing CuO/ZnO catalysts", Journal of Catalysis 223 (2004), pg 340351 Matter, P.H., Ozkan, U.S., " Effect of Pre-treatment Conditions on Cu/Zn/Zr- Based Catalysts for the Steam Reforming of Methanol to H2", Journal of Catalysis 234 (2005), pg 463-475 Matter, P H., Ling Zhang, and Umit S Ozkan, “The Role of Nanostructure in Nitrogen-Containing Carbon Catalysts for the Oxygen Reduction Reaction”, Journal of Catalysis 239 (2006), pg 83-96 v Matter, P H., and Umit S Ozkan, “Non-metal Catalysts for Dioxygen Reduction in an Acidic Electrolyte”, Catalysis Letters, in press Matter, P H., Eugenia Wang, Maria Arias, Elizabeth J Biddinger, and Umit S Ozkan, “Oxygen Reduction Reaction Catalysts Prepared from Acetonitrile Pyrolysis Over Alumina Supported Metal Particles”, Journal of Physical Chemistry B, submitted Matter, P.H., J.-M Millet, and U.S Ozkan, “Non-metal catalysts for oxygen reduction reaction in PEM fuel cells” in 16th World Hydrogen Energy Conference (2006), Lyon, France, submitted Matter, P H., Elizabeth J Biddinger, and Umit S Ozkan, “Non-precious metal oxygen reduction catalysts for PEM fuel cells”, Catalysis – Volume 20 (2006), edited by Jerry J Spivey, The Royal Society of Chemistry, Cambridge, UK, in preparation Matter, P H., Eugenia Wang, Maria Arias, Elizabeth Biddinger, and Umit S Ozkan, “Preparation of Nanostructured Nitrogen-Containing Carbon Catalysts for the Oxygen Reduction Reaction from SiO2 and MgO Supported Metal Particles”, Journal of Catalysis, submitted Matter, P H., Eugenia Wang, Maria Arias, Elizabeth Biddinger, and Umit S Ozkan, “Oxygen Reduction Reaction Activity and Surface Properties of Nanostructured Nitrogen-Containing Carbon” to be submitted to the Journal of Molecular Catalysis FIELDS OF STUDY Major Field: Chemical Engineering Area of Interest: Heterogeneous Catalysis vi TABLE OF CONTENTS Page ABSTRACT ii ACKNOWLEDGMENTS iv VITA v LIST OF TABLES xi LIST OF FIGURES xiii VOLUME I: ANOSTRUCTURED NITROGEN-CONTAINING CARBON CATALYSTS FOR THE OXYGEN REDUCTION REACTION IN PROTON EXCHANGE MEMBRANE FUEL CELL CATHODES CHAPTER – INTRODUCTION 1.1 Advantages of Fuel Cells 1.2 How a PEM Fuel Cell Works 1.3 Shortcomings of Current PEM Fuel Cells 11 CHAPTER – LITERATURE REVIEW 15 2.1 Non-Noble Metal Cathode Materials 15 2.1.1 Macrocycles 15 2.1.2 Pyrolyzed Macrocycles 19 2.1.3 Non-macrocyclic Heat Treated Catalysts 29 2.1.4 Conducting Polymers 40 2.2 Nitrogen Surface Species 41 2.3 Potential Role of Nanostructure 45 CHAPTER – EXPERIMENTAL METHODS 55 3.1 Catalyst Preparation 55 3.1.1 Carbon Supported Materials 56 3.1.2 Alumina Supported Materials 57 3.1.3 SiO2 Supported Materials 59 vii 3.1.4 MgO Supported Materials 60 3.1.5 Unsupported Materials 60 3.2 Catalyst Characterization 61 3.2.1 Thermo-Gravimetric Analysis of in situ Pyrolysis 62 3.2.2 Thermo-Gravimetric Analysis of Precursors 62 3.2.3 Temperature Programmed Acetonitrile Pyrolysis 63 3.2.4 Weight Change Analysis 63 3.2.5 N2 Physisorption Experiments 64 3.2.6 X-Ray Diffraction 64 3.2.7 Temperature Programmed Oxidation 64 3.2.8 Raman Spectroscopy 65 3.2.9 Mössbauer Spectroscopy 65 3.2.10 Hydrophobicity Testing 66 3.2.11 X-ray Photoelectron Spectroscopy 67 3.2.12 Transmission Electron Microscopy 67 3.3 Electrochemical Testing 68 3.3.1 Conductivity Testing 68 3.3.2 Rotating Disk Electrode Half Cell Testing 69 3.3.3 Rotating Ring-Disk Electrode Testing 72 3.3.4 Lab Scale Proton Exchange Membrane Fuel Cell Testing 73 CHAPTER – RESULTS AND DISCUSSION 75 4.1 Carbon Supported Catalysts 75 4.1.1 Effect of Fe on Acetonitrile Pyrolysis 75 4.1.2 Bulk Physical Characterization 85 4.1.3 Activity Testing Results 92 4.1.4 Surface Characterization 99 4.1.5 TEM Imaging 105 4.1.6 PEM Fuel Cell Testing 109 4.2 Alumina Supported Catalysts 110 4.2.1 Determination of Acceptable Treatment Parameters using TGA 110 4.2.2 By-Products of Acetonitrile Pyrolysis 115 4.2.3 Treatment Parameters Examined 121 4.2.4 Morphological Characterization 124 4.2.5 Bulk Physical Characterization 128 4.2.6 Characterization of the Fe phase with Mössbauer Spectroscopy 134 4.2.7 Surface Characterization 143 4.2.8 TEM Imaging 146 4.2.9 Hydrophobicity Testing 159 4.2.10 Electrochemical Testing Results 160 4.2.11 RRDE Selectivity Testing 172 4.2.12 Methanol Oxidation Activity 176 4.2.13 Conclusion from Analysis of CNx Prepared from Alumina Supports 178 4.3 Silica and Magnesia Supported Catalysts 179 viii 4.3.1 Pyrolysis By-Products 179 4.3.2 Preparation Parameters 180 4.3.3 N2 Physisorption Analysis 181 4.3.4 X-ray Diffraction Analysis 184 4.3.5 Bulk Analysis Using Temperature Programmed Oxidation 185 4.3.6 TEM Imaging 193 4.3.7 Surface Characterization 202 4.3.8 Hydrophobicity Testing 207 4.3.8 Electrochemical Properties 209 4.3.9 Conclusion from Analysis of CNx Prepared Using Silica and Magnesia Supports 213 4.4 Other Materials Prepared 214 4.4.1 Phosphorus-doped carbon 214 4.4.2 Stacked platelet carbon 216 CHAPTER – CONCLUSIONS 221 CHAPTER – RECOMMENDATIONS 223 VOLUME II: TEAM REFORMING OF METHANOL TO HYDROGEN OVER ZIRCONIA-CONTAINING Cu/ZnO-BASED CATALYSTS 226 ABSTRACT 227 CHAPTER – INTRODUCTION 229 7.1 Hydrogen from Methanol 229 7.2 Cu/ZnO-Based Catalysts 230 CHAPTER – LITERATURE REVIEW 233 CHAPTER – EXPERIMENTAL METHODS 236 9.1 Catalyst Preparation 236 9.2 Cu Surface Area Measurements 237 9.3 X-ray Diffraction 238 9.4 Temperature Programmed Desorption 239 9.5 TGA-DSC of Precursor Decomposition 239 9.6 TGA-DSC of Catalyst Reduction 240 9.7 XPS Analysis 241 9.8 Diffuse Reflectance Infrared Fourier Transform Spectroscopy 241 9.9 Activity Testing 242 9.10 Time-On-Stream Activity Testing 243 CHAPTER 10 – RESULTS AND DISCUSSION 244 ix 161 Rodriguez, N.M., A Chambers, and R.T.K Baker, Catalytic Engineering of Carbon Nanostructures Langmuir, 1995 11: p 3862-3866 162 Baker, R.T.K., Kim, M.S., Chambers, A., Park, C., Rodriguez, N.M., The Relationship Between Metal Particle Morphology and the Structural Characteristics of Carbon Deposits Studies in Surface Science and Catalysis, 1997 111: p 99-109 163 Chambers, A., T Nemes, N.M Rodriguez, and R.T.K Baker, Catalytic Behavior of Graphite Nanofiber Supported Nickel Particles Comparison with Other Support Media Journal of Physical Chemistry B, 1998 102(12): p 2251-2258 164 Baker, R.T.K., M.A Barber, P.S Harris, F.S Feates, and R.J Waite, Nucleation and Growth of Carbon Deposits from the Nickel Catalyzed Decomposition of Acetylene Journal of Catalysis, 1972 26: p 51-62 165 Baker, R.T.K., P.S Harris, R.B Thomas, and R.J Waite, 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and sample after the pyrolysis = C The weight gain was then calculated using the following equation: % weight gain = ((C – B) + (% lost from TGA) * (B – A )) / (C – A) 332 To measure the conductivity of a sample, the powder sample is pressed between two copper plates creating a pellet of known dimensions The voltage is swept from 0.0 to 0.1 V, and the final current is reported, measured by a potentiostat The conductivity can then be calculated as follows: Rabsolute = ( 0.1 V / (final current in Amps)) – RCu plates [=] Ohms where RCu plates = 0.307 Ohms Rintrinsic = Rabsolute * Cross Sectional Area / Length [=] Ohms * cm Where: Cross Sectional Area = π * (0.325 cm)2 Length = 0.015 cm Conductivity = (100 cm / m ) / Rintrinsic [=] S / m 333 ... these fuel cells are unique from the other commercially viable types of fuel cells, like the Solid Oxide Fuel Cell (SOFC), the Phosphoric Acid Fuel Cell (PAFC), and the Molten Carbonate Fuel Cell... source of fuel for the cells and the corresponding infrastructure must be developed Since fuel cells are merely energy conversion devices, they are only as clean and efficient as the upstream fuel. .. Schematic drawing of how a PEM fuel cell works (a) (b) (c) Figure 2: Characteristic curves for a typical PEM fuel cell 10 1.3 Shortcomings of Current PEM Fuel Cells Fuel cells have several economical