2D Black Phosphorus as Source of Phosphide Atoms to Afford Mixed Cobalt Phosphides Clusters Active in the Photocatalytic Hydrogen Evolution

The use of solar energy to produce valuable feedstocks and among others, energy vectors, 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 phosphides clusters having different stoichiometry, Co2P and CoP with sub-nanometric size. In depth study at atomic level by X-Ray Absorption Spectroscopy and electron microscopy confirmed the nature and structure of the phosphides, revealing as well that Co2P/CoP functionalization contributed to efficiently hinder the spontaneous degradation of BP in ambient conditions. Under simulated solar light irradiation, the hydrogen evolution rate of BP@CoxP integrated with TiO2, reached 5.3 mmol/g·h, almost 30-fold than TiO2. Electrochemical and photoluminescence investigation elucidated the electronic properties of the photocatalyst, showing the mixed CoxP phases led to an increased charge density across the heterostructure, a lowering of the conduction band energy that infers more reducing power, and the generation of multiple interfaces that increases the charge transfer and diminish the electron-hole recombination.