Self-supporting Fe,Co co-doped Ni3S2 nanosheet arrays as advanced bifunctional electrocatalysts for alkaline seawater splitting

Abstract

The critical factor in realising hydrogen production through alkaline seawater electrolysis lies in the development of highly active and anti-corrosion catalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Herein, this work reports on an S-FeCoNi/NF-1.0 material—a Ni₃S₂ compound co-doped with Fe and Co—synthesized via a simple two-step hydrothermal-sulphidation process, which forms a uniformly grown, interconnected nanosheet array on nickel foam. S-FeCoNi/NF-1.0 achieves minimal overpotentials of 224/211 mV@100 mA cm⁻² for the OER and the HER in 1.0 M KOH seawater, and retains steady-state operation under conditions of 500 h@0.1 A cm⁻² upon integration into a two-electrode HER||OER system. The construction of the three-dimensional array and the co-doping of Fe and Co significantly augment the electrode-active surface area and effectively modulate the electronic structure of the resulting electrocatalyst. At the same time, the sulphide passivation layer formed on the surface of S-FeCoNi/NF-1.0 repels Cl⁻, thereby enabling sustained and stable oxygen evolution whilst suppressing corrosion and evolution of chlorine. This work provides an engineering strategy for enhancing the electrocatalytic activity of ternary metallic sulphides in high-chloride seawater environments.