An electron-hole rich dual-site nickel catalyst for efficient photocatalytic overall water splitting

Photocatalysis offers an attractive strategy to upgrade H₂O to renewable fuel H₂. However, current photocatalytic hydrogen production technology often relies on additional sacrificial agents and noble metal cocatalysts, and there are limited photocatalysts possessing overall water splitting performance on their own. Here, we successfully construct an efficient catalytic system to realize overall water splitting, where hole-rich nickel phosphides (Ni₂P) with polymeric carbon-oxygen semiconductor (PCOS) is the site for oxygen generation and electron-rich Ni₂P with nickel sulfide (NiS) serves as the other site for producing H₂. The electron-hole rich Ni₂P based photocatalyst exhibits fast kinetics and a low thermodynamic energy barrier for overall water splitting with stoichiometric 2:1 hydrogen to oxygen ratio (150.7 μmol h^-1 H₂ and 70.2 μmol h^-1 O₂ produced per 100 mg photocatalyst) in a neutral solution. Density functional theory calculations show that the co-loading in Ni₂P and its hybridization with PCOS or NiS can effectively regulate the electronic structures of the surface active sites, alter the reaction pathway, reduce the reaction energy barrier, boost the overall water splitting activity. In comparison with reported literatures, such photocatalyst represents the excellent performance among all reported transition-metal oxides and/or transition-metal sulfides and is even superior to noble metal catalyst.