Cr-doped NiFe sulfides nanoplate array: Highly efficient and robust bifunctional electrocatalyst for the overall water splitting and seawater electrolysis

To replace precious metals and reduce production costs for large-scale hydrogen production, developing stable, high-performance transition metal electrocatalysts that can be used in a wide range of environments is desirable yet challenging. Herein, a self-supported hybrid catalyst (NiFeCrSx/NF) with high electrocatalytic activity was designed and constructed using conductive nickel foam as a substrate via manipulation of the cation doping ratio of transition metal compounds. Due to the strong coupling synergy between the metal sulfides NiS2, Fe9S11, and Cr2S3, as well as their interaction with the conductive nickel foam (NF), the energy barrier for catalytic reactions is reduced, and the charge transfer rate is enhanced. This significantly improves the hydrogen evolution reaction (HER) performance of NiFeCrSx/NF, achieving a current density of 10 mA cm-2 with an overpotential of just 66 mV. Furthermore, doping with chromium generates different valence states of Cr during the catalytic process, which can synergize with the high-valent Fe and Ni, promoting the formation of oxygen vacancies and enriching the active sites for the oxygen evolution reaction (OER). Consequently, at a current density of 10 mA cm-2 in 1.0 M KOH, the overpotential for OER is only 223 mV for NiFeCrSx/NF. Additionally, the in situ grown of self supporting nanoflower structure on NiFe-LDH not only provides a large catalytic surface area but also facilitates electrolyte penetration during the catalytic process, endowing NiFeCrSx/NF with high long-term stability. When used as a bifunctional catalyst for overall water splitting, the NiFeCrSx/NF||NiFeCrSx/NF electrolyzer requires only 1.29 V to deliver a current density of 10 mA cm- 2. Simultaneously, Cr doping protects the Fe sites by maintaining stable valence states, ensuring high performance and stability of NiFeCrSx/NF, even when it is utilized for seawater splitting. This strategy offers novel concepts for creating catalysts based on non-precious metals that can be utilized in various application scenarios.