Wide-pH-compatible MoSx co-catalyst layer on TiO2 nanowire arrays photoanode for simultaneous acceleration of charge carrier separation and catalytic reactions

The water oxidation reaction is a key reaction for solar water splitting, which requires excellent oxygen evolution co-catalyst to accelerate charges separation efficiency and high catalytic reaction sites for O2 releasing. So far, many earth-abundant co-catalysts can only play roles at a single pH (only in neutral or alkaline electrolyte), but the development of wide-pH compatible co-catalyst with low price are rarely obtained. Herein, amorphous MoSx layer was conformally coated on TiO2 nanowire arrays (NAs) as an active co-catalyst for multi-pH water photo-oxidation. The experimental results showed that the MoSx greatly enhanced the photoelectrochemical (PEC) performance of TiO2 NAs with high photocurrent densities of 1.95, 1.67, and 1.55 mA/cm2 at 1.23 VRHE in acidic, alkaline, and neutral electrolyte, respectively, significantly higher than bare TiO2 and most TiO2/co-catalyst literature values. Density functional theory (DFT) calculations revealed that the MoSx on TiO2 improves electronic interaction at their interface and forms a type-II band structure for more efficient separation of charge carriers. It is also found that high-density active sites provided by MoSx can reduce the Gibbs free energy and overpotential of potential-determining step for OER, which further enhance the adsorption activity of reaction intermediates. Our work contributes to the in-depth understanding of amorphous MoSx as efficient water oxidation co-catalyst for multi-pH PEC water splitting.