Porous MoS ₂ /Co ₈ FeS ₈ Heterojunction as Bifunctional Electrocatalyst for Energy‐Saving Hydrogen Production Coupled With Sulfur Recovery

Abstract The oxidation reaction of sulfide ions holds significant potential for replacing kinetically sluggish water oxidation, substantially reducing power consumption of hydrogen production by electrocatalytic water splitting. Herein, a hierarchical MoS 2 /Co 8 FeS 8 bifunctional sulfion‐tolerant electrocatalyst on nickel foam (MoS 2 /Co 8 FeS 8 /Ni 3 S 2 /NF) is constructed for the oxidation of water, urea, and S 2− . Benefiting from the engineered p‐p/Schottky dual heterojunctions and its porous structure, the MoS 2 /Co 8 FeS 8 /Ni 3 S 2 /NF material possesses the optimized electronic structure at interface between the MoS 2 and Co 8 FeS 8 ,, thus presenting excellent electrocatalytic performance including hydrogen evolution reaction (HER), urea oxidation reaction and sulfion oxidation reaction (SOR). The formed heterojunction between MoS 2 and Co 8 FeS 8 leads to the clear observation of electron transfer from Co 8 FeS 8 to MoS 2 . The MoS 2 /Co 8 FeS 8 /Ni 3 S 2 /NF material as anode and cathode exhibits an ultralow voltage of 0.477 V at 100 mA cm −2 in sulfion‐assisted two‐electrode water splitting cell with superior energy efficiency being of merely 1.147 kWh m −3 H 2 energy consumption, which represents over 60% energy saving compared to conventional water splitting system. What's more, this kind of water splitting cell owns a superior stability in the continuous 200 h operation. UV–vis spectroscopy and X‐ray diffraction patterns reveal the gradual oxidation of S 2− to short‐chain polysulfions (S n 2− , 2 ≤ x ≤ 4), ultimately forming S 8 . Density functional theory calculations elucidate that the MoS 2 /Co 8 FeS 8 heterojunction possesses the optimized SOR pathway with a lower energy barrier compared to MoS 2 and Co 8 FeS 8 , and best H* adsorption free energy, as well as low energy barrier of water dissociation. This approach offers new possibilities for treating sulfion‐containing industrial wastewater and developing energy‐saving hydrogen production technology.