Co3(OH)2(HPO4)2 as a novel photocatalyst for O2 evolution under visible-light irradiation

Abstract

Cobalt phosphate has shown great potential as an electrocatalyst or a cocatalyst loaded on a photocatalyst for O₂ evolution, but has not yet been successfully used as a photocatalyst for O₂ evolution so far. Herein, a kind of cobalt phosphate, i.e., Co₃(OH)₂(HPO₄)₂ (Co₃(PO₄)₂·2H₂O), was prepared by a simple hydrothermal method, and was proved to be a novel, stable photocatalyst for O₂ evolution under visible-light irradiation for the first time. The photocatalytic mechanism of Co₃(OH)₂(HPO₄)₂ was revealed by comprehensively comparing the physicochemical properties of Co₃(OH)₂(HPO₄)₂ with those of another kind of cobalt phosphate, i.e., Co₃(PO₄)₂·8H₂O, which was prepared by a precipitation method and showed little photocatalytic activity for O₂ evolution under visible-light irradiation. The significantly improved photocatalytic activity of Co₃(OH)₂(HPO₄)₂, compared with that of Co₃(PO₄)₂·8H₂O, was mainly attributed to the synergistic promotion of the photocatalytic process by the following physicochemical properties of Co₃(OH)₂(HPO₄)₂, i.e., the distortion of Co²⁺ octahedra, the difference in electronic properties and the linkage of oxo bridges between the adjacent Co(1) and Co(2) octahedra. This work extended the application of cobalt phosphate in photocatalysis and presented an effective route to explore new O₂-evolution photocatalysts by modifying the appropriate materials that were commonly employed as cocatalysts.