Insights into the Ir-O redox dynamics of an operating PEM water electrolyzer using in operando Raman spectroscopy

In operando Raman investigations of iridium-based oxygen evolution (OER) catalysts in water electrolysis offer insights into catalytically relevant species and pathways, enabling optimization towards effective use of iridium. This work builds upon existing academic studies by utilizing industrially relevant proton exchange membrane catalyst-coated membrane electrode assemblies in an applicable cell design. To overcome challenges in spectral analysis, a methodology for spectral deconvolution with a focus on stability and validity was developed and verified by two-dimensional correlation analysis. Based on in operando studies during potential-dependent electrolysis and catalyst relaxation at open circuit potential, the oxygen evolution reaction pathway on iridium-based catalyst-coated membrane electrode assemblies was found to involve a concerted redox reaction of both iridium and oxygen. Formation of the active species occurs from iridium oxo-hydroxides and crystalline IrO₂ via oxidative charging. Enhanced proton conduction due to ionomer presence in application-oriented systems promotes deprotonation, causing oxidative charging of the catalyst well before the oxygen evolution reaction onset.