<i>In situ</i> activation-induced surface reconstruction on Cr-incorporated Ni₃S₂ for enhanced alkaline hydrogen evolution reaction

Ni₃S₂ has emerged as one of the most promising hydrogen evolution reaction (HER) catalysts due to its moderate activity, exceptional electrical conductivity, and scalable synthesis methods. However, the high energy barrier for H₂O dissociation and weak desorption of the H* intermediate severely hinder its HER kinetics. In this study, a novel Cr-incorporated Ni₃S₂ was grown on a Ni mesh substrate (denoted as Cr-Ni₃S₂/NM) using a one-step electrodeposition approach, resulting in a large surface area with abundant Ni₃S₂/Cr₂S₃ heterojunctions. Subsequently, it underwent surface reconstruction after <i>in situ</i> activation (denoted as A-Cr-Ni₃S₂/NM), which not only enhanced charge and mass transfer but also altered the electronic structure by introducing more oxygen species on the catalyst surface and creating S vacancies. Using theoretical calculations, this <i>in situ</i> activation was shown to not only promote charge transport but also boost HER kinetics by strengthening OH* desorption for H₂O dissociation and facilitating the desorption of H* intermediates. As a result, the fabricated A-Cr-Ni₃S₂/NM demonstrated exceptional HER performance with a small overpotential of 78 mV to deliver a current density of -10 mA cm^-2, along with stability for over 200 h at 100 mA cm^-2. While surface reconstruction has been intensively studied in catalysts for the oxygen evolution reaction, we illustrate that it also plays a significant and positive role in Cr-Ni₃S₂ HER catalysts in this study, thus providing a pathway for achieving high-performance HER catalysts.