Nickel sulfide–transition metal sulfides bi-electrocatalyst supported on Nickel Foam for water splitting

Developing electrochemical devices for renewable energy relies on essential improvements in electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this work, a series of prepared electrocatalysts composed of nickel sulfide and transition metal sulfides (NiS_x-MS_x/rGO-ST, where M = Zn, Co, Mn, or Fe) were supported on reduced graphene oxide (rGO) and silica template (ST). A modified solution method coupled with the thiourea-phosphate-assisted solvothermal route was used for the preparation process. NiS–ZnS/rGO-ST/NF showed a low overpotential of 161 mV at 10 mA cm^-2 for the HER. Further, for OER, the overpotential of 324 mV was obtained by NiS–FeSO₄/rGO-ST/NF at 50 mA cm^-2. Moreover, all studied electrocatalysts showed negligible deterioration for the 60 h stability test, indicating outstanding HER and OER performance. The water splitting system composed of NiS–ZnS/rGO-ST/NF//NiS–FeSO₄/rGO-ST/NF electrodes had good performance with ∼1.77 V at 10 mA cm^-2, which was close to that of a noble metal-based Pt/C/NF//RuO₂/NF water splitting system (1.75 V at 10 mA cm^-2). The excellent electrocatalytic activity of the resulting electrocatalysts was mainly due to the enhancement of both mass and charge transfer for HER and OER, which promotes the interaction between water molecules and electrocatalyst reactive sites. This study provides an exclusive approach to designing high-performance and stable electrocatalysts for HER and OER.