Concentrating electron and activating H-OH bond of absorbed water on metallic NiCo2S4 boosting photocatalytic hydrogen evolution

As a metallic cocatalyst, the photothermal effect of NiCo2S4 in the process of photocatalytic hydrogen evolution has not been deeply discussed elsewhere. It has been well known that how to intrinsically speed the photo-generated electrons transfer and active absorbed Water (*H2O) to release more hydrogen proton (*H) are extremely meaningful to photocatalytic hydrogen evolution improvement. Herein, a convenient and mild two-step solvothermal strategy was developed to meticulously design the intimate contact structure between a noble-metal-free cocatalyst NiCo2S4 and semiconductor ZnIn2S4 nanoflower, which facilitates the charge rear-rangement at the interface to boost the separation of photogenerated carriers. Importantly, photothermal effect induced by NiCo2S4 was demonstrated to ameliorate slow kinetics of water spilling with the apparent activation energy reduction form 50.5 kJ.mol(-1) to 38.8 kJ.mol(-1), which was responsible for improving photocatalytic hydrogen evolution rate of 6834.6 mu mol.g(-1).h(-1) accompanied by apparent quantum efficiency of 13.0% at 400 nm. The electron transfer was accelerated due to localized electric field enhancement determined by Finite difference time domain (FDTD) simulations. The decline of Gibbs free energy barrier of adsorbed water from 2.94 eV on ZIS to 1.62 eV on NCS/ZIS resulted in H-OH bond activating was demonstrated using density functional theory (DFT). This work will provide an effective pathway to design semiconductor-metal-based photothermal assisted photocatalytic system and expand the application of metallic NiCo2S4 in solar-to-fuel conversion.

Automated summary

This study developed a convenient and mild two-step solvothermal strategy to design a metal-assisted photocatalytic system. The photothermal effect of the metallic cocatalyst improved the kinetics of water splitting, resulting in an enhanced photocatalytic hydrogen evolution rate.