Enhanced photocatalytic hydrogen production via MnCdS/NiSe heterojunctions: A synergistic effect of promoting water dissociation and electron - Hole separation

The efficiency enhancement of photocatalytic hydrogen evolution reaction (HER) fundamentally relies on accelerating photogenerated charge separation and optimizing water adsorption-activation processes to generate reactive hydrogen species (H∗). The mechanistic understanding of interfacial water dissociation dynamics, particularly the synergistic effects of adsorption, activation, and proton transfer, remains critically underexplored. Herein, we demonstrate an innovative heterojunction system through rational design of non-stoichiometric Ni_0·85Se co-catalysts anchored onto Mn_0·4Cd_0·6S (MCS) solid solutions. The optimized Ni_0·85Se/MCS hybrid achieves an exceptional HER rate of 42.5 mmol/g/h under visible light, representing a 3.34-fold enhancement over pristine MCS. Combined experimental characterization and DFT calculations reveal that the work function difference drives directional electron transfer from MCS to Ni_0·85Se, while coordinatively Ni sites preferentially adsorb and dissociate H₂O molecules through optimized d-band positioning. Crucially, the metastable Ni-Se configuration regulates the adsorption/desorption energetics of key intermediates (H∗, OH∗), establishing a dual-functional platform that simultaneously enhances charge separation efficiency and lowers the water dissociation energy barrier. This work provides atomic-level insights into interfacial water activation mechanisms and establishes fundamental guidelines for designing multifunctional co-catalysts in solar-driven hydrogen production systems.