Characterization of Oxygen and Ion Mass Transport Resistance in Fuel Cell Catalyst Layers in Gas Diffusion Electrode Setups

Fuel cell catalyst layers contain an essential active catalyst, a support material for electron conductivity, ionomer for proton conductivity, and porosity for gas transport, which build up complex interfaces that determine the overall performance. Subtle variations in the processing of the catalyst layers can significantly alter the performance, which demands intensive research efforts, and requires considerable amount of time. In the last few years, gas diffusion electrode (GDE) half-cell setups have been introduced as a promising approach to speed up catalyst layer evaluation. Yet, advanced methods to thoroughly characterize transport phenomena within the catalyst layer have not been established for GDE half-cell setups. In the present work, we adapt electrochemical characterization methods, such as O (2) transport resistance and CO-displacement, which have been previously developed for single cell testing, to enable unique insights into catalyst layers' structure-performance relationships with the GDE method. Utilizing a commercial Pt/Vulcan catalyst as a test system, we identify the cause of mass transport limitations due to different ionomer contents. We show that an intermediate I/C ratio of 0.70, which forms a thin layer of ionomer, leads to an optimal performance for the Vulcan carbon support, due to an optimal compromise between O-2 and proton accessibility.