Developing a series of calcium-doped pyrochlore iridates for the oxygen evolution reaction in PEM water electrolysis

Abstract

Active and stable catalysts for the oxygen evolution reaction (OER) with reduced precious metal content are crucial for green hydrogen production. State-of-the-art OER catalysts used in proton exchange membrane water electrolysis (PEMWE) like ruthenium oxides and iridium oxides either show insufficient stability in the acidic environment or exhibit high cost due to their high iridium-content. In recent studies, iridium-containing pyrochlores (A2Ir2O7) gained interest as possible OER catalysts for PEMWE, due to their high activity at reduced iridium content compared to IrO2. Although several doping strategies were found to boost the OER properties of the pyrochlore ruthenates even further, few studies have focused on the iridates, yet. While doping degrees were limited to one specific composition in the iridate case so far, we herein we present a series of six praseodymium iridates (Pr2Ir2O7) where we systematically replaced A-site Pr3+ with Ca2+. Electrochemical measurements with a rotating disk electrode (RDE) demonstrate that the Ca-doping has a positive effect on the mass activity of the material. Simultaneously, iridium dissolution, evidenced by inductively coupled plasma mass spectrometry (ICP-MS), is significantly reduced by the doping. We report an up to 100% increase in the stability number (S-number) when compared to the undoped catalyst. This work presents a promising perspective to further enhance pyrochlore iridates as efficient OER catalysts for water splitting.