Nickel nanoparticles coated with graphene layers as efficient co-catalyst for photocatalytic hydrogen evolution

Metallic nickel nanoparticles well dispersed in graphitized carbon matrix (Ni@C) by pyrolysis of metal-organic frameworks and leaching treatment of hydrochloric acid could greatly enhance the photocatalytic activity of g-C₃N₄ under visible light irradiation. For 2.0 wt% Ni@C/g-C₃N₄, the average hydrogen evolution rate is 2.15 mmol h⁻¹ g⁻¹, which is around 88 times higher than that of pure g-C₃N₄, and even better than that of platinum-loaded g-C₃N₄. The remarkably improved photocatalytic activities through loading Ni@C can be attributed to the cooperative work of Ni nanoparticles and graphene layers, which facilitate the separation of photo-generated carriers and suppress the recombination of the electron-hole pairs. In addition, the hollow onion-like structure can restrain the formation of Ni-hydrogen bonds which modulates desorption of hydrogen. Our studies may open up a promising strategy to design economical noble-metal-free co-catalysts for efficient solar energy conversion.