Composed of earth-abundant elements, many metal phosphides have revealed remarkable advantages as photocatalytic hydrogen generation cocatalysts for their outstanding performance, stability and low cost. Taking the importance for solar energy utilization and current synthetic methods of metal phosphides into consideration together, we focus on the safe and energy-saving preparation of metal phosphide as cocatalyst for photocatalytic hydrogen evolution. Herein, taking CoxP/CdS as a case, a novel photochemical strategy to synthesize CoxP is proposed and realized. In this process, Co salt and NaH2PO2 are used as the source of Co and P, and the typical preparation of CoxP can be completed within 1 h. Furthermore, the optimized hydrogen evolution rate of CoxP/CdS is about 500 mmol g 1 h(-1) under visible light, which is one of the most robust photocatalytic HER systems currently. Besides, the photocatalytic H-2 evolution mechanism using CoxP as cocatalyst is also proposed, where CoxP can effectively prevent the recombination of photogenerated electrons and holes. The photochemical synthesis route opens a door for facile preparation and practical application of many other metal phosphides. (C) 2017 Elsevier B.V. All rights reserved.