Enhancing photocatalytic H2 evolution by weakening S–Had bonds via Co-induced asymmetric electron distribution in NiCoS cocatalysts

The intrinsic symmetrical electron distribution in crystalline metal sulfides usually causes an improper electronic configuration between catalytic S atoms and H intermediates (H_ad) to form strong S-H_ad bonds, resulting in a low photocatalytic H₂ evolution activity. Herein, a cobalt-induced asymmetric electronic distribution is justified as an effective strategy to optimize the electronic configuration of catalytic S sites in NiCoS cocatalysts for highly active photocatalytic H₂ evolution. To this end, Co atoms are uniformly incorporated in NiS nanoparticles to fabricate homogeneous NiCoS cocatalyst on TiO₂ surface by a facile photosynthesis strategy. It is revealed that the incorporated Co atoms break the electron distribution symmetry in NiS, thus essentially increasing the electron density of S atoms to form active electron-enriched S^(2+δ)– sites. The electron-enriched S^(2+δ)– sites could interact with H_ad via an increased antibonding orbital occupancy, which weakens S–H_ad bonds for efficient H_ad adsorption and desorption, endowing the NiCoS cocatalysts with a highly active H₂ evolution process. Consequently, the optimized NiCoS/TiO₂(1:2) photocatalyst displays the highest H₂ production performance, outperforming the NiS/TiO₂ and CoS/TiO₂ samples by factors of 2.1 and 2.5, respectively. This work provides novel insights on breaking electron distribution symmetry to optimize catalytic efficiency of active sites.