Electrochemical Active Surface Area Determination of Iridium-Based Mixed Oxides by Mercury Underpotential Deposition

The electrochemical surface area (ECSA) is a critical property to describe, analyze and compare electrocatalysts. The determination of the mass activity of a given catalyst is associated with this parameter which can thus lead to materials benchmarking. Reliable and robust methods to measure ECSA are needed, and those have to accommodate different structures, morphologies and compositions. In this study, we investigate mercury underpotential deposition (Hg_UPD) as a way to estimate ECSA for ultraporous electrocatalysts based on iridium and iridium-molybdenum electrocatalysts for the oxygen evolution reaction. Results reveal a clear agreement between physisorption measurements and Hg_UPD with excellent reproducibility. The method shows also that pre- and post-catalysis surface area measurements are not affected by the catalytic process on short timescale, opening the possibility of electrocalyst stability and degradation monitoring.