Mass-transport resistances of acid and alkaline ionomer layers: A microelectrode study part 1 - Microelectrode development

One of the most critical issues limiting widespread commercialization of polymer-electrolyte fuel cells is catalyst cost, which is directly related to dominant unexplained local gas and ion transport resistances at low catalyst loading (1). These resistances are believed to be highly correlated to the ionomer thin films in the catalyst layer. Unfortunately, current understanding of transport resistances in the catalyst layer is largely inferred from limiting current experiments employing heterogeneous, complex and multi-interfaced membrane electrode assemblies. An alternative study providing a more localized probe and promising fundamental insight is the microelectrode method (2). Ionomer thin film-coated microelectrodes can simulate an idealized thin film operating condition similar to that found at the platinum/ionomer interface in the catalyst layer of a typical fuel cell. In this work, an in-house, custom-made microelectrode setup with good humidity, temperature and potential control is used to determine the transport coefficient of hydrogen and oxygen gas across the ionomer thin film layer. The set-up is also capable of examining gas transport and evaluating the impact of ion activity on electrochemical kinetics in both acid and alkaline conditions, making it ideal for expanded understanding of gas and ion transport in both polymer electrolyte membrane and alkaline anion exchange fuel cells, respectively. A. Z. Weber and A. Kusoglu, J. Mater. Chem. A., 2, 17207 (2014). D. Novitski and S. Holdcroft, ACS Appl. Mater. Interfaces, 7, 27314 (2015). Acknowledgements: This study was partially funded under the Fuel Cell Performance and Durability Consortium (FC-PAD) funded by the Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U.S. Department of Energy under contract number DE-AC02-05CH11231.