Engineering the transition metal hydroxide–photoanode interface with a highly crystalline mediator for efficient photoelectrochemical water splitting

Abstract

Coating transition metal hydroxides (TMHs) onto semiconductor (SC) photoanodes is an ideal approach to improve photoelectrochemical (PEC) water splitting. Nevertheless, the obtained system still suffers from inevitable interface charge recombination and the sluggish surface reaction. Herein, we report a one-stone-two-birds strategy to engineer the SC/TMH/electrolyte interface for highly efficient PEC performance through introducing high crystallinity Fe(OH)_X-H. In situ ultraviolet/visible-spectroelectrochemistry and electrochemical analyses show that Fe(OH)_X-H, like a “hole transporter”, directly transfers charge to the TMH surface via a modulated charge transfer pathway rather than as a traditional hole accumulation layer, which not only efficiently inhibits interface charge recombination, but boosts water oxidation kinetics. As expected, the BiVO₄/Fe(OH)_X-H/FeNi(OH)_X photoanode achieves a noteworthy photocurrent density of 5.34 mA cm⁻² (1.23 V_RHE, AM 1.5G) along with long-term stability. Notably, this strategy can be applied to the BiVO₄/Fe(OH)_X-H/CoFe(OH)_X system. This work affords a useful inspiration for modulating charge transfer behavior in the PEC water splitting field.