Contamination of Low Platinum Catalyst Loading Cathodes for Proton Exchange Membrane Fuel Cells

Abstract

Fuel cell vehicles have recently entered the market place (1). Future increases in technology adoption are dependent on concurrent cost reduction and improved durability (2). This is a major challenge because membrane/electrode assemblies based on low platinum catalyst loadings have shown inferior durability (3). Many processes limit the proton exchange membrane fuel cell (PEMFC) durability including the presence of contaminants in ambient air. Although a filter is added at the air intake to remove particulates and undesirable gaseous species, contaminant slippage, missed replacements after the filter has reached its end of life and other failures increase fuel cell exposure risks. A strategy relying on the understanding of contamination mechanisms is expected to result in a more robust system with the development of mitigation, recovery and maintenance procedures that supplement the air filter. Such a strategy is necessary because the impact of many contaminants is still unknown (4). Furthermore, relatively little contaminant related information is available for low platinum catalyst loadings (5-7). In this tutorial, focus will be given to recent contamination results and fundamental understanding obtained with a low cathode platinum loading of 0.1 mg cm-2, a value consistent with the United States Department of Energy 2020 target of 0.125 mg cm-2 for the sum of anode and cathode catalyst loadings. All tested contaminants are organic and representative of alcohols (iso-propanol), alkenes (propene), alkynes (acetylene), esters (methyl methacrylate), halocarbons (bromomethane), nitriles (acetonitrile), and polycyclic aromatics (naphthalene). The impact of catalyst loading and contaminant on cell performance, contaminant hydrophobicity on liquid water transport, a long duration contaminant exposure on degradation, a fuel cell stack compatible recovery procedure on cell voltage losses sustained during contamination, and a contaminant mixture on the synergy between species and cell performance will be discussed and contextualized with the relevant literature. All these contamination aspects have either not been explored or been insufficiently documented. Acknowledgments Authors are grateful to the Office of Naval Research (award N00014-13-1-0463), the Department of Energy (award DE-EE0000467), the National Institute of Standards and Technology (neutron imaging beam time), and the Hawaiian Electric Company for their ongoing support to the operations of the Hawaii Sustainable Energy Research Facility.