Bridged planar [Ni(CN)4]2- coordination active site to promote photocatalytic hydrogen evolution of transition metal sulfides

The spatial photoinduced charge separation and atomic H 2 evolution active site is decisive in the operating efficiency of the photocatalytic hydrogen evolution reaction, yet its rational design and synthesis remain a grand challenge. Here, a series of Hofmann-type coordination polymers (HCPs) with planar anionic block [Ni(CN) 4 ] 2- units were found to effectively enhance the photocatalytic H 2 evolution reaction (PHER) activity of transition metal sulfides (TMSs). This proof-of-concept study investigated four HCPs with planar anionic block [Ni(CN) 4 ] 2- units combined with different central transition metal ion (M 2+ : Ni, Co, Fe, and Mn). All four HCP-modified TMSs exhibited remarkable PHER activity of more than 20.0 mmol g −1 ·h −1 and an apparent quantum yield of ∼20 %, surpassing that of optimized Pt/Zn 0.5 Cd 0.5 S by more than 1.5-fold. Through spectroscopic characterization, Kelvin probe force microscopy (KPFM), and density functional theory (DFT) simulations, we confirmed that the [Ni(CN) 4 ] 2- units potentially bridged with the TMSs via an M-S bond forming an electronic transmission channel, thus eliminating the interface energy barrier. Due to the appropriate band structure, the photogenerated electrons converged to the [Ni(CN) 4 ] 2- units, consequently facilitating the conversion of H + to H 2 . This work demonstrates a rational synthetic route for creating PHER photocatalysts that possess mild synthesis conditions, efficient electronic transmission interfaces, and an active center that can be finely manipulated.