Advances in structural and chemical analysis of catalystcoated membranes for hydrogen fuel cell applications

Catalyst-coated membranes are a key element of advanced membrane electrode assembly designs for automotive, hydrogen-based fuel cell systems. The morphology of the catalyst layers of these membranes should provide a structure that is optimised for maximum catalyst utilisation; water management at a wide range of operational temperatures and relative humidity; fuel (hydrogen) and oxidant (oxygen in air) mass-transfer; and optimum electronic conductivity. Because of the multi-component nature of the layers (catalyst, ionomer and catalyst support) and resulting hierarchy in the layered structure at different spatial scales, new tools for their characterisation are required. Such a development should lead to an improved understanding of the links between fuel cell performance and structure of the catalyst layers under various operating conditions. This feature article presents soft X-ray spectromicroscopy as a tool for such studies and shows how it can probe the structural and chemical properties of the membrane and the catalyst layers of membrane electrode assemblies.