3D Nitrogen-Anion-Decorated Nickel Sulfides for Highly Efficient Overall Water Splitting

Developing non-noble-metal electrocatalysts with high activity and low cost for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is of paramount importance for improving the generation of H₂ fuel by electrocatalytic water-splitting. This study puts forward a new N-anion-decorated Ni₃S₂ material synthesized by a simple one-step calcination route, acting as a superior bifunctional electrocatalyst for the OER/HER for the first time. The introduction of N anions significantly modifies the morphology and electronic structure of Ni₃S₂, bringing high surface active sites exposure, enhanced electrical conductivity, optimal HER Gibbs free-energy (ΔG_H*), and water adsorption energy change (ΔG_H2O*). Remarkably, the obtained N-Ni₃S₂/NF 3D electrode exhibits extremely low overpotentials of 330 and 110 mV to reach a current density of 100 and 10 mA cm⁻² for the OER and HER in 1.0 m KOH, respectively. Moreover, an overall water-splitting device comprising this electrode delivers a current density of 10 mA cm⁻² at a very low cell voltage of 1.48 V. Our finding introduces a new way to design advanced bifunctional catalysts for water splitting.

Metallic N-anion decorated Ni₃S₂ brings high surface active site exposure, enhanced conductivity, optimal hydrogen evolution reaction (HER) Gibbs free-energy, and water adsorption energy change, acting as superior bifunctional electrocatalysts for the HER/oxygen evolution reaction (OER). The metallic N-Ni₃S₂/NF 3D electrode only needs a low cell voltage of 1.48 V to reach the current density of 10 mA cm⁻², which is superior to most Ni-based electrode materials.

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