2D black phosphorus as a phosphide source for the formation of mixed cobalt phosphide clusters active in...

The use of solar energy to produce valuable feedstocks and energy vectors, such as hydrogen, is a fascinating research field of utmost practical importance. Herein, we report a facile strategy to functionalize 2D black phosphorus nanosheets (BPNS) with mixed cobalt phosphide clusters of different stoichiometry, Co₂P and CoP, with sub-nanometric sizes. The in-depth study at the atomic level by X-ray absorption spectroscopy and electron microscopy confirmed the nature and structure of the phosphides and revealed that Co₂P/CoP functionalization effectively hindered the spontaneous degradation of BP under ambient conditions. Under simulated solar-light irradiation, the hydrogen evolution rate of BP@Co_xP integrated with TiO₂ reached 5.3 mmol g^-1 h^-1, almost 30-fold higher than that of TiO₂. Electrochemical and photoluminescence investigations elucidated the electronic properties of the photocatalyst, showing that the mixed Co_xP phases led to increased charge density across the heterostructure, a lower conduction band energy, which infers more reducing power, and the generation of multiple interfaces, which increase charge transfer and reduce electron-hole recombination.