Surface selectivity of Ni3S2 toward hydrogen evolution reaction: a first-principles study.

Exploring materials with high catalytic performance toward hydrogen evolution reaction (HER) is of importance for the development of clean hydrogen energy, and their surface structure is essential for this function. In this study, using density functional theory (DFT), we reported a comprehensive study on the phase stability, surface structures, electronic properties and HER catalytic properties of the low-index surfaces of Ni3S2, including the (0001), (101[combining macron]0), (101[combining macron]1), (112[combining macron]0) and (112[combining macron]1) planes with different terminations. Our calculated results demonstrate that S-rich surfaces and several stoichiometric surfaces of Ni3S2 are thermodynamically stable, including (0001)A, (101[combining macron]0)A, (112[combining macron]0)C, (101[combining macron]0)C, (101[combining macron]0)B and (112[combining macron]1)A surfaces. Among the six stable surface structures, the (0001)A, (101[combining macron]0)B and (101[combining macron]0)C surfaces of Ni3S2 are indispensable for high HER performance because of their high catalytic activity, suitable potential and high thermodynamic stability. The calculated changes of Gibbs free energy (ΔGH*) of the Top S2 site on (0001)A, Hollow Ni2S3S4 site on (101[combining macron]0)C, and Bridge Ni1Ni3 site and Hollow Ni2S1S2 site on (101[combining macron]0)B are -0.143, 0.122, 0.012, and -0.112 eV, respectively, comparable with or even better than those of Pt(111) (-0.07 eV). In addition, the possible Volmer-Heyrovsky and Volmer-Tafel processes on the considered surfaces are also investigated. When the overpotential is in the range of 0 to 300 mV, the density of active sites on the (101[combining macron]0)B surface of Ni3S2 is found to be the highest. This work provides significant insights on the surface selectivity of Ni3S2 toward HER and provides a route to optimize the performance of Ni3S2 with exposed surfaces.