Crystal phase of nickel sulfide dictates hydrogen evolution activity of various semiconducting photocatalysts

Abstract

Phase engineering can overcome the weaknesses of catalysts by tuning the electronic structures and catalytic functions. In this study, we investigate the role of phase-engineered NiS_x, specifically hexagonal, trigonal and cubic phases, as a cocatalyst decorated onto the semiconductor surface. We demonstrate that NiS_x with different phases (i.e. h-NiS, t-NiS and c-NiS₂) can greatly improve the photocatalytic hydrogen evolution rate of various classical semiconductors including TiO₂, CdS and carbon nitride (CN). In particular, it is observed that c-NiS₂ can promote the H₂ evolution performance with the highest improvement factor compared with h-NiS and t-NiS regardless of the type of hosting semiconductor. The highly efficient sacrificial hydrogen evolution performance rates are achieved on c-NiS₂/CN (4078 μmol h⁻¹ g⁻¹), c-NiS₂/TiO₂ (345 μmol h⁻¹ g⁻¹) and c-NiS₂/CdS (14 604 μmol h⁻¹ g⁻¹) under light irradiation (λ > 320 nm). As revealed by detailed characterizations and theoretical computations, the significant higher performance of c-NiS₂ is because c-NiS₂ possesses more appropriate hydrogen adsorption Gibbs free energy and better ability in facilitating charge migration compared to h-NiS and t-NiS. Our findings highlight the great potential of phase engineering as a general strategy for improving the catalytic performance of different catalysts.