Ultra-high overpotential induces NiS2 deep reconstruction to significantly improve HER performance

It is well known that transition metal sulfides (TMS) (i.e., NiS₂) undergo electrochemical reconstructions to generate highly active Ni₃S₂ during the process of hydrogen evolution reaction (HER) under overpotentials of < 500 mV. However, at higher overpotentials, Ni₃S₂ can theoretically be further restructured into Ni and thus form Ni/Ni₃S₂ heterogeneous interface structures, which may provide opportunities to further enhance HER activity of NiS₂. Here, we selected NiS₂ as a model electrocatalyst and investigated the influence of the reconstruction results induced from regular to ultrahigh overpotentials on its electrocatalytic hydrogen precipitation performance. The experimental results showed that the most significant enhancement of hydrogen precipitation performance was obtained for the NiS₂@CC-900 (900 means 900 mV overpotential) sample after the ultra-high overpotential induced reconstruction. Compared with the initial overpotential of 161 mV (10 mA cm^–2), the overpotential of the reconstructed sample reduced by 67 mV (42%). The characterization results showed that an ultra-high overpotential of 900 mV induced deep reconstruction of NiS₂, formed highly reactive Ni/Ni₃S₂ heterogeneous interfaces, which is more conducive to improved HER performance and match well with theoretical calculations results. We demonstrated ultrahigh overpotential was an effective strategy to induce NiS₂ deeply reconstruction and significantly improve its HER performance, and this strategy was also applicable to CoS₂ and FeS₂. This study provides an extremely simple and universal pathway for the reasonable construction of efficient electrocatalysts by induced TMS deeply reconstruction.