Cobalt and sulfur co-doping induce nickel electron localization to enhance alkaline hydrogen evolution activity.

[Display omitted] • Cobalt and sulfur co-doped Ni electrocatalysts were designed and synthesized. • Ni-Co-S electrocatalysts exhibited the enhanced HER performance. • Role of doped S in inducing electron localization of Ni was demonstrated. • Co and optimized Ni were verified to be active sites in Volmer and Heyrovsky steps, respectively. Developing and synthesizing the economical electrocatalysts for alkaline hydrogen evolution reaction (HER) is essential for the large-scale production of hydrogen source. Although NiCoS-based electrocatalysts have attracted great attention, deep insight into the mechanism of boosted HER activities still needs to be further investigated, especially based on the doped Ni-based electrocatalyst. Herein, we synthesized the cobalt and sulfur co-doped nickel electrocatalysts (NCS) and the HER performance is evaluated in alkaline medium. The results show that the NCS with optimized component has a boosted HER activity compared to Ni, NiCo, and NiS, which exhibits the lower overpotential of 45.8 mV at 10 mA·cm−2 and Tafel slope of 83.4 mV·dec-1. The co-introduced Co and S are conductive to increase the reactive sites, charge transfer capacity and aerophobic property. The theoretical calculation results reveal that the doped S can induce electron localization at the Ni and Co atoms bonded to S atom. Moreover, we also confirm that the Co sites and Ni sites of NCS represent the reactive sites in the Volmer and Heyrovsky steps, respectively, and thereby boosting the hydrogen evolution activity. The obtained insights could provide a significant guideline for designing highly efficient electrocatalyst toward alkaline hydrogen evolution. [ABSTRACT FROM AUTHOR]