Contact Problems of IrOx Anodes in Polymer Electrolyte Membrane Water Electrolysis

Abstract

Green-hydrogen production by polymer electrolyte membrane water electrolysis (PEMWE) is limited by the use of expensive Ir-based catalysts, presenting a key challenge in achieving a low-IrOx-loaded membrane electrode assembly (MEA). Here, we investigate the abnormally poor performance and large high-frequency impedances in the ultralow-IrOx-loaded MEA (as low as 0.07 mg cm–2) for PEMWE. We reveal that these primarily originate from the electron transport problem in the native oxide on the Ti porous transport layer (PTL). Based on the metal–insulator band model, we conclude that the upward band bending by the Schottky contact with the high-work-function IrOx and the pinch-off effect by massive ionomer contact are the major causes of electron conductivity loss of the Ti oxide. This study highlights the importance of the catalyst/PTL interface and reveals that modulation of the catalyst work function and ionomer distribution is necessary to achieve high-performing but cheap water electrolysis.