Preparation and Operando Imaging of Pt-Bimetallic Oxygen Reduction Catalysts for Polymer Electrolyte Fuel Cell

Polymer electrolyte fuel cell (PEFC) is key for clean energy production using hydrogen for carbon-neutral society. Electrocatalysts with Pt have been used as efficient catalysts for both electrodes in membrane electrode assembly (MEA), which has a stacking structure of anotde catalyst layer, electrolyte membrane, and cathode catalyst layer. Under practical PEFC operating conditions with lots of water and fuels, various events proceed in MEA such as catalysis at both electrodes, surface redox reactions of Pt electrocatalysts, dissolution, migration, and aggregation of Pt electrocatalysts, water flooding, deactivation of electrocatalysts by air contaminants, formation of unfavorable radical species, and migration of radical scavenger. The optimization of reaction controls on electrocatalysts are essential for efficient PEFC performances. Compared to anode conditions, cathode reactions with oxygen often bring about degradation of cathode electrocatalysts and the developments of cathode catalysts with durable performances under PEFC operation conditions are still challenging.<br/>In this paper, I present the preparation and electrochemical performances of Pt-bimetallic electrocatalysts for PEFC and operando imaging of electrocatalysts under PEFC working conditions. The use of hard X-rays enables to visualize these events inside MEA under PEFC operating conditions, and the recent examples of 3D imaging of PEFC MEA by operando XAFS-CT spectroimaging will be presented.