Comparison of methods to determine electrocatalysts’ surface area in gas diffusion electrode setups: a case study on Pt/C and PtRu/C

In recent years, gas diffusion electrode half-cell setups have attained increasingattention bridging the gap between fundamental and applied fuel cell research. They allowquick and reliable evaluation of fuel cell catalyst layers and provide a unique possibilityto screen different electrocatalysts at close to real experimental conditions. However,benchmarking electrocatalysts’ intrinsic activity and stability is impossible withoutknowing their electrochemical active surface area (ECSA). In this work, we compare andcontrast three methods for the determination of the ECSA: (a) underpotential depositionof hydrogen (Hupd); (b) CO-stripping; and (c) underpotential deposition of copper (Cuupd)in acidic and alkaline electrolytes, using representative electrocatalysts for fuel cellapplications (Pt and PtRu-alloys supported on carbon). We demonstrate that, while allmethods can be used in gas diffusion electrode setups, CO-stripping is the mostconvenient and reliable. Additionally, the application of Cuupd offers the possibility toderive the atomic surface ratio in PtRu-alloy catalysts. By discussing the advantages ofeach method, we hope to guide future research in accurately determining surface areaand, hence, the intrinsic performance of realistic catalyst layers