Improving Reactant and Proton Transport in Catalyst Layers for Direct Alcohol Fuel Cells

Abstract

Direct alcohol fuel cells (DAFC) produce electricity from liquid fuels such as methanol, ethanol etc., where the alcohol is oxidized at the anode and oxygen is reduced on the cathode side of the fuel cell. Operation of alcohol fuel cells is attractive because of the exceptionally high volumetric energy density and easy handling of liquid fuels in comparison to pressurized hydrogen. [1] Especially direct methanol fuel cells (DMFC) have been widely investigated as portable power sources. However, even with these relatively simple fuels, the reaction kinetics of the electro-oxidation are slow in comparison to hydrogen oxidation. Furthermore, DAFC suffer from severe reactant crossover through the membrane, leading to low open circuit voltages and poor overall performance. [2] In order to solve crossover issues, manufacturing of various composite membranes and additional alcohol blocking layers become more and more important in this research field. [3] Nonetheless, also understanding and improving reactant and proton transport in catalyst layers for DAFCs is very important in order to improve current densities and reduce costs, as less expensive platinum group metal catalysts are needed. Commonly, very high loadings on the anode side of DAFC result in thick catalyst layers, which suffer from poor reactant transport and high proton resistances and flooding, especially in the high current density regions. Our work to be presented is focused on novel architectures of membrane electrode assemblies (MEAs) for applications in direct alcohol fuel cells to target these problems and improve the physical properties of the catalyst layer with a focus on different ionomers, different ionomer contents, and pore size distribution. [1] R. P. O'Hayre, F. B. Prinz, S.-W. Cha, W. G. Colella, Fuel cell fundamentals, Third edition ed., Wiley, Hoboken, 2016. [2] C. Xu, A. Faghri, X. Li, T. Ward, International Journal of Hydrogen Energy 2010, 35, 1769–1777. [3] P. Prapainainar, N. Pattanapisutkun, C. Prapainainar, P. Kongkachuichay, International Journal of Hydrogen Energy 2019, 44, 362–378.