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 BiVO 4 /Cu-CoO x /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-CoO x , like “charge transporter”, can directly modulate charge transfer pathway and quickly transfer hole from BiVO 4 to FeNiOOH surface for PEC water splitting. Moreover, the approach can be extended to other Cu-NiO x and Mn-CoO x , proving its universality. This work provides an effective strategy to design efficient and stable photoanodes for water splitting.