Contact Problems of IrOX Anodes in Polymer Electrolyte Membrane Water Electrolysis

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.