Dendritic gold-supported iridium/iridium oxide ultra-low loading electrodes for high-performance proton exchange membrane water electrolyzer

[Display omitted] •Ir loading on Au dendrite is simply controlled in micro-gram scale.•Specific OER activities are significantly affected by Ir electronic structure.•Extremely high OER mass activities are obtained in half cell and single cell test.•They significantly exceed the mass activities of state-of-the-art Ir-based anodes. The insufficient performance of current oxygen evolution reaction (OER) electrodes limits the realization of clean hydrogen production via proton exchange membrane water electrolyzers (PEMWEs). Herein, an innovative electrode design with an ultra-low Ir loading is proposed to achieve high catalytic OER performance, catalyst utilization, conductivity, and mass transfer. The microgram-scale loading of Ir on a highly roughened dendritic Au support is controlled by the number of Ir deposition pulses and, together with Ir coverage, which significantly affect the Ir electronic structure and intrinsic OER activity. Further control of the Ir electronic structure is achieved by forming Ir oxides via electrochemical and thermal oxidation to adjust the activity–stability balance. A PEMWE employing the fabricated electrode demonstrates substantially low ohmic and mass-transfer losses, especially in the higher-current-density region. As a result, superior cell performance with extremely high mass activity is achieved, significantly exceeding the mass activities of state-of-the-art Ir-based anodes.