Revealing the role of Sn in NiSn for enhancing hydrogen evolution performance by density functional theory

Abstract

Doping Sn into transition metal Ni can gain an enhanced hydrogen evolution performance. Optimizing H binding free energy (ΔGH) is considered as the main function of Sn. However, the detailed action mechanism of Sn in NiSn catalyst is still ambiguous. Herein, the functional role of Sn in NiSn was systematically inspected using density functional theory (DFT) method. The difference site Ni of Ni slab was replaced by Sn to build NiSn with the difference distribution of Sn. The calculations about the barrier of H2O dissociation and ΔGH show that surface Ni in NiSn is the main active site for catalyzing the hydrogen evolution reaction (HER) and the distribution of Sn in NiSn alloy directly decides the main role of Sn in promoting HER. Only replacing surface Ni with Sn, the main role of Sn is to reduce the adsorption of H and promote the H desorption step of HER. When Sn locates at sub-surface or surface and sub-surface Sn exist simultaneously, ΔGH on NiSn has no reduction and accelerating the H2O dissociation is the main function of Sn.