Multivalent Rh@RhO_<i>x</i> and MnO_<i>x</i>-Modified CdS for Robust and Efficient Photocatalytic Hydrogen Evolution

Rh is considered an effective HER active site, but the impact of the oxide layer formed by exposure to air on HER has been ignored. Here, Rh@RhOx and MnOx are used to enhance the hydrogen evolution reaction (HER) activity of CdS by vacuum photodeposition method. We leverage the built-in electric field generated between the supporter and cocatalysts, as well as the valence state transitions of multivalent cocatalysts, to achieve maximum photocarrier separation. Through in situ XPS, H2O-TPD, ESR, LSV, and TPV, the roles of Rh@RhOx and MnOx were thoroughly investigated. First, Rh@RhOx and MnOx act as reducing and oxidizing cocatalysts, respectively. Second, water (H2O) adsorption and activation are accomplished on their surfaces. Third, RhOx facilitates the formation of adsorbed H2 (Hads), while MnOx efficiently consumes photogenerated holes (h+) through the generation of hydroxyl radicals (·OH). At their maximum effective concentrations, photogenerated electrons interact with Hads and H2O to generate H2. The hydrogen evolution rate of the optimal sample (R0.7CM1.5) was 78.95 mmol·g–1·h–1, which was 415 times higher than that of CdS. This study provides a convenient and feasible modification scheme for commercially available HER photocatalysts.