Insights into the charge transfer kinetics in BiVO₄ photoanodes modified with transition metal-based oxygen evolution electrocatalysts

BiVO₄ is a promising photoanode for photoelectrochemical (PEC) water splitting. Nevertheless, the sluggish water oxidation on its surface causes severe charge carriers recombination and thus reduces the overall efficiency. To overcome these imperfections, BiVO₄ photoanodes were prepared and modified with transition metal-based oxygen evolution electrocatalysts, namely, NiFe, CoNi, and CoFe–layered double hydroxides (LDHs) oxygen evolution catalysts (OECs). The kinetics of charge transfer and recombination in the prepared photoanodes were studied by transient photocurrent and intensity-modulated photocurrent spectroscopy (IMPS). The rate constants of charge transfer and recombination were determined and correlated with the generated photocurrent to disclose the function of each electrocatalyst. It was concluded that the three investigated LDHs exhibit a comparable electrocatalytic activity at low applied potential, but CoNi–LDH has a superior passivation effect. Contrary to CoFe and NiFe–LDHs, CoNi–LDH passivates the surface states and unpins the Fermi level as proved by IMPS and photovoltage measurements. This study provides a systematic pathway to disclose the role of LDH OECs on BiVO₄ surface which is an essential step for the rational design of efficient photoanodes.