(Plenary) Doing More with Less: Challenges for Catalyst Layer Design

Abstract

Proton exchange membrane (PEM) fuel cells are being developed as alternative energy sources for both residential and automotive application. In order for this technology to become fully commercial, the reduction of cost and improvements in performance and durability of PEM fuel cells membrane electrode assemblies (MEAs) are still required. To address the requirement for further cost reduction the Pt loading of the cathode catalyst layer (CCL) needs to be reduced to 0.2- 0.1 mg/cm2 while maintaining high efficiency of Pt-utilization at high power densities. Consequently, it becomes increasingly important to not only develop new catalyst materials, but also optimize the 3D structural arrangement of the CCL components such as catalyst, ionomer and void space so that all critical functionalities can be achieved simultaneously and optimize PGM utilization. In general terms this entails to provide sites catalytically active for ORR, and to further provide transport to/these sites for the reactants O2, protons, electrons and products H2O and heat, respectively. In order to be able to design CCL structures that meet the performance and durability requirements, it is necessary to obtain a better understanding of structure versus performance relationships. This requires the capability to fabricate different CCL structures, to characterize the spatial distribution of all components within the catalyst layer1,2 (carbon, Pt, ionomer and void), to measure the physico-chemical properties (both ex-situ and in-situ) and finally to use these experimental data as inputs for the development a model based understanding of the relationship between CCL structure and CCL performance and durability3. References A. P. Hitchcock, V. Berejnov, V. Lee, D. Susac and J. Stumper, “In situ methods for analysis of polymer electrolyte membrane fuel cell materials by soft X-ray scanning transmission x-ray microscopy”, Microscopy & Microanalysis 20(S3) 1532 (2014)V. Lee, V. Berejnov, M. West, S. Kundu, D. Susac, J. Stumper, R.T. Atanasoski, M. Debe and A.P. Hitchcock, “Scanning Transmission X-ray Microscopy of Nano Structured Thin Film Catalysts for Proton-Exchange-Membrane Fuel Cells” J. Power Sources 263 163 (2014)S. G. Rinaldo, W. Lee, J Stumper, M. Eikerling: “Nonmonotonic dynamics in Lifshitz-Slyozov-Wagner theory: Ostwald ripening in nanoparticle catalysts” Physical Review E 86, 041601 (2012)