Effect of Processing on Electrochemistry and Surface Chemistry of PGM-Free Catalyst for Oxygen Reduction Reaction

Rising oil prices, limited reserves of oil, and evidence of global warming due to human contribution and carbon emissions motivate the need for alternative energies. For automobiles, there is interest in creating a completely electric vehicle that is not dependent on fossil fuels. Fuel cells are one type of technology that could address this. A fuel cell converts chemical energy directly to electrical energy, using hydrogen or another liquid (e.g. methanol, ethanol, etc from renewable sources such as biomass) as a fuel and produces only water as the final product. Fuel cells still face challenges for large scale implementation because of platinum, therefore another electrocatalyst that is active, durable, and cost-efficient must be found. Platinum-group-metals-free (PGM-free) catalysts based on a low-cost transition metal (e.g. Fe, Mn, Co, and Ni) on a carbon-nitrogen rich support were found to be promising alternative. The catalysts are synthesized using the sacrificial support method (SSM). After pyrolysis of the organic precursor with the metallic salt, the template is etched to create open-ended pores and well-defined catalyst morphology. Improvement of catalyst synthesis relies on an understanding of how the catalyst changes by each processing step during preparation, and the relationship between catalytic activity, surface chemistry, and morphology. Rotating ring disk electrode (RRDE) experiments and x-ray photoelectron spectroscopy (XPS) were conducted on samples taken from each step of the preparation process. After these measurements are obtained, correlations between surface chemistry, catalytic activity, and processing were investigated. The results discuss the effect of pyrolysis, etching, and grinding on the catalyst performances for future improvements.