Boosting photocatalytic water oxidation over bifunctional Rh0-Rh3+ sites.

Photocatalytic water splitting provides an economically feasible way for converting solar energy into hydrogen. Great efforts have been devoted to developing efficient photocatalysts; however, the surface catalytic reactions, especially for the sluggish oxygen evolution reaction (OER), still remains as a big challenge, which limits the overall photocatalytic energy efficiency. Here, we design a kind of Rhn cluster cocatalyst, with bifunctional Rh0-Rh3+ sites anchoring on the Mo-doped BiVO4 model photocatalytic system. The resultant photocatalyst enables a super high visible-light photocatalytic oxygen production activity of 7.11 mmol g-1 h-1 and an apparent quantum efficiency of 29.37% at 420 nm. Besides, the turnover frequency (TOF) value of the excellent photocatalyst could achieve 416.73 h-1, which is 378 times higher than that of the photocatalyst only decorated with Rh3+ species. The experimental and theoretical results unambiguously demonstrate the existence of stable isolated Rhn cocatalyst with Rh0-Rh3+ sites, and the operando X-ray absorption characterization proves the OER process on the bifunctional Rh0-Rh3+ sites. The density functional theoretical calculations further illustrate a bifunctional OER mechanism over the Rh0-Rh3+ sites, in which the oxygen intermediate attacks the Rh3+ sites with assistance of a hydrogen atom transfer to the Rh0 sites, thus breaking the scaling relationship of various oxygen intermediates. This work demonstrates the potential of bifunctional Rh0-Rh3+ sites to circumvent the OER scaling relationship to construct high-performance photocatalysts or photoelectrodes.