Unveiling the promotion of dual-metal-atom Ir-Fe pair sites on charge transfer for photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting is a key step for developing a carbon-neutral and sustainable energy system. Despite the essential metal dispersion provided by single-atom catalysts, further enhancement of PEC performance, including charge separation and transfer, can be limited by the lack of neighboring metal atoms in photoelectrodes originating from serious charge recombination and sluggish reaction kinetics. Herein, we constructed dual-metal-atom (DMA) Ir-Fe pair sites loaded on hematite for a superior PEC activity with an onset potential of 0.56 V versus reversible hydrogen electrode and an applied bias photon-to-current conversion efficiency of 1.00%. DMA Ir-Fe pair sites are taken as the potential alternative activity contributors for promoting PEC activity. Experiments and density functional theory demonstrate that the synergistic effect between Ir and Fe with strong electronic coupling accelerates charge separation and transfer while allowing the key OH∗ intermediate to desorb over the iridium site and overcoming charge recombination at the interface.