Functional nickel iron sulphide/hydroxide catalysts for hydrazine oxidation and energy saving hydrogen production†

Electrocatalytic water splitting is a promising technique for green hydrogen production, yet its efficiency is hindered by the sluggish oxygen evolution reaction (OER) at the anode. This study advocates an efficient strategy to address this challenge by developing a NiFe-hydroxide/sulfide heterostructure (NFS@NF) catalyst directly grown on nickel foam via a one-pot chemical bath deposition technique. The optimized NiFe-hydroxide/sulfide shows obvious catalytic performance, requiring overpotentials of 150 mV at a current of 10 mA cm⁻² for hydrogen evolution. Additionally, the NFS@NF exhibits low potentials for the OER (1.45 V vs. RHE), urea oxidation (1.35 V vs. RHE), and hydrazine oxidation (0.26 V vs. RHE) at 100 mA cm⁻². These exceptional catalytic activities are attributed to the synergy between nickel and iron and sulfur-induced modifications in chemical states and the local structure. A full-cell configuration generates 10 mA cm⁻² current at 1.57 V for water electrolysis, which can be further reduced to 1.44 V and 0.37 V by substituting conventional electrolysis of water with electrolysis of urea and hydrazine, respectively. The electrodes exhibit excellent durability, maintaining stable catalytic performance for 70 hours at 300 mA cm⁻² for water electrolysis and 100 mA cm⁻² for hydrazine electrolysis. Additionally, its application in an Mg/seawater battery shows stable discharge for 16 hours with a power density of 4.02 mW cm⁻², which provides the required power for hydrazine electrolysis. Finally, this research offers an efficient, earth-abundant catalyst solution for sustainable hydrogen production and energy storage applications, advancing hybrid water-splitting and Mg/seawater battery technologies.