Highly Active and Stable Iridium Pyrochlores for Oxygen Evolution Reaction

Proton exchange membrane water electrolysis (PEMWE) is a promising technology for electricity-to-fuel conversion which allows for direct production of hydrogen from water. One of the key problems limiting widespread implementation of PEMWE into energy systems is the sluggish kinetics of the anodic process: the oxygen evolution reaction (OER). Additionally, state-of-the-art OER materials contain large amounts of low abundant noble metals (Ru, Ir), and therefore, development of low-cost, highly active and stable OER catalysts remains an important challenge. We developed a synthetic approach to the iridium pyrochlores–complex oxides of iridium with reduced content of the noble metal as compared to IrO₂. The materials were synthesized from molten sodium nitrate (Adams fusion method) at moderate temperatures (500–575 °C) and consist of highly crystalline iridium pyrochlore nanoparticles with surface areas of up to 40 m² g^–1, which is a significant improvement compared to the traditional high temperature solid-state synthesis. Electrochemical measurements in acidic media showed that yttrium and bismuth pyrochlore catalysts possess high OER activity approaching the activity of state-of-the-art IrO₂ nanoparticles. High intrinsic activities and stability behavior of yttrium iridium catalysts were correlated with the formation of the highly active IrO_x surface layer due to leaching of the Y³⁺ cations into the electrolyte solution, revealed both experimentally and computationally using density functional theory calculations.