Asymmetric Bridging Multi-Active Sites in a-NiSeS Cocatalyst for Upgrading Photocatalytic H2 Evolution

Abstract

Cocatalyst-coupled photocatalytic system offers an attractive tactic to produce eco-friendly H₂ fuel from renewable water and sunlight. However, the efficiency of single homologous active site in current cocatalysts is seriously restricted by the opposite binding-energy requirement for hydrogen adsorption and desorption. Herein, an asymmetric strategy of bridging multi-active sites is validated to break the strong relevancy of H adsorption–desorption rate on the designed amorphous NiSeS (a-NiSeS) cocatalyst. It is found that the S–Ni–Se modules with self-optimized electron-rich S^(2+δ)− and electron-deficient Se^(2-δ)− atoms can induce the transfer of hydrogen from S^(2+δ)− to Se^(2-δ)− sites for synchronously realizing the fast H adsorption and desorption. Consequently, the TiO₂/a-NiSeS photocatalyst delivers a significantly enhanced H₂-evolution activity of 8216 µmol h⁻¹ g⁻¹, which is 2.5 and 3.3 times higher than that of TiO₂/a-NiS and TiO₂/a-NiSe, respectively. The improved activity is ascribed to the unique synergistic mechanism of asymmetric bridging multi-active sites, namely, S^(2+δ)− site works as the hydrogen-rich center, thermodynamically neutral bridge site of S–Ni–Se functions as the mediator for rapidly transferring H from S^(2+δ)− to Se^(2-δ)−, while the Se^(2-δ)− site expedites the desorption of hydrogen to free H₂. This work provides atomic-level insight into the underlying cocatalytic mechanism of H adsorption and desorption.