Low oxidation state engineering in transition metal-based interfacial regulation layer accelerates charge transfer kinetics toward enhanced photoelectrochemical water splitting

The loading of transition metal oxyhydroxide (TMOH) on semiconductor (SC) is a promising strategy for fabricating desired photoelectrochemical (PEC) devices. Nevertheless, the inevitable charge recombination occurring at SC/TMOH interface severely hinders the carrier transfer. Herein, differing from the conventional multi-step hole capture process, a novel transition metal-based interfacial regulation layer with low oxidation state species is introduced for boosted charge separation. As expected, the optimized BiVO4/Cu-CoOx/FeNiOOH photoanode obtains a photocurrent density of 6.60 mA/cm(2) at 1.23 V versus reversible hydrogen electrode (RHE) accompanied with outstanding photostability. In-situ ultraviolet/visible-spectroelectrochemistry, electrochemical analyses, and density functional theory (DFT) show that the Cu-CoOx, like "charge transporter", can directly modulate charge transfer pathway and quickly transfer hole from BiVO4 to FeNiOOH surface for PEC water splitting. Moreover, the approach can be extended to other Cu-NiOx and Mn-CoOx, proving its universality. This work provides an effective strategy to design efficient and stable photoanodes for water splitting.