Mass transport characterization of platinum group metal-free polymer electrolyte fuel cell electrodes using a differential cell with an integrated electrochemical sensor

A method to enable in place measurements of the mass transport resistance for platinum group metal (PGM)-free polymer electrolyte fuel cell electrodes is presented. Thin platinum black layers deposited at the membrane interface served as electrochemical sensors, performing hydrogen oxidation, for hydrogen probe gas molecules while PGM-free catalyst materials, being electro-inactive to hydrogen oxidation, were probed for mass transport resistance through the full layer. Theoretical considerations, assumptions, and future applications of the methodology are discussed. The method is demonstrated on catalyst layers fabricated from a commercially available PGM-free oxygen reduction catalyst. Effective diffusivity measurements using hydrogen were made which were then used to estimate the effective diffusivity of air of the full layer without the confounding effect of electrode flooding. This method complements alternative techniques such as mercury porosimetry or x-ray computed tomography and can be easily adopted by research groups everywhere to study MEA-level properties of PGM-free catalyst layers and accelerate the development and deployment of PGM-free PEFCs.