| Summary: | It is considered that the oxidation activity of Ir based anodes on H2 permeating the polymer electrolyte membrane (PEM) in PEM water electrolyzers (WE) is poor, resulting in high H2-in-O2 contents at idle or dynamic operating conditions, especially with asymmetric pressure. In the present work, the dependence of H2 permeation on cathode pressure was quantified by the pressure drop method. H2 consumption was detected by chronoamperometry at potentials preceding water splitting. The addition of N2 in the anode outlet gas allowed the on-line monitoring of the mixture composition during idle PEMWE operation by a thermal conductivity sensor. It is found that H2 is effectively consumed with IrOx oxyhydroxide anodes at low current densities, with 75% conversion of the zero-current permeation at cathode pressure of 5 bar and 60 °C. Hence, both H2-in-O2 content and lowest current density at which the H2-in-O2 flammability limit is not exceeded decrease by more than 50%. Current density corrections accounting for H2 consumption and mass transport potential corrections accounting for the enhancement of H2 permeation with current density were implemented. The resulting Tafel slope values suggest that the rate determining step of the oxygen evolution reaction with IrOx oxyhydroxides is a chemical step. Keywords: PEMWE, H2 permeation, H2 consumption, Mass transport, Tafel slope, IrOx oxyhydroxides
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