An Fe3S4/Ni3S2 heterostructure realizing highly efficient electrocatalysis of ethylene glycol and alkaline electrolyte to produce high value-added chemicals and hydrogen

Abstract

Electrocatalytic water splitting is considered a green and promising strategy for hydrogen production. Replacing the sluggish oxygen evolution reaction (OER) with a thermodynamically favorable ethylene glycol oxidation reaction (EGOR) enables energy-saving hydrogen production coupled with high-value formate generation. Herein, a self-supported Fe₃S₄/Ni₃S₂ (NiFeS) heterojunction electrocatalyst was successfully synthesized through a facile one-pot solvothermal strategy. The interconnected nanosheets covered by fused flakes with uneven surfaces maximize the exposure of electroactive sites during the OER and the EGOR. Therefore, the electrode only requires a low OER overpotential of 240 mV to afford a current density of 100 mA cm⁻² in 1.0 M KOH electrolyte, and can work stably for 120 h. Furthermore, only 1.37 V vs. RHE was required to achieve a current density of 100 mA cm⁻² in 1.0 M KOH + 1.0 M ethylene glycol electrolyte, and the highest Faraday efficiency (92.4%) and rapid productivity (0.652 mmol cm⁻² h⁻¹) could be achieved for formate production at an applied potential of 1.50 V vs. RHE. The Raman spectroscopy indicated that the metal oxyhydroxides (NiOOH and FeOOH) generated by surface reconstruction and metal sulfides are the real active species of the OER and the EGOR, respectively. The coupled electrolysis system involving the HER (commercial Pt/C electrode) and the EGOR (NiFeS electrode) outputs a current density of 100 mA cm⁻² at 1.55 V, which is 140 mV lower than that of the traditional water electrolysis system. This study puts forward a rational strategy for preparing heterojunction catalysts for energy-saving H₂ and value-added formate production from alkaline media.