Mo-doped cobaltous sulfide nanosheet arrays as efficient catalysts for the sulfion oxidation reaction promoting hydrogen production with ultra-low electric energy consumption

Constructing efficient coupling systems based on the hydrogen evolution reaction (HER) and the sulfion oxidation reaction (SOR) to realize low-cost hydrogen production could promote the rapid development of the hydrogen economy. However, sulfion is prone to poisoning the active site, leading to a decline in catalytic activity and inferior catalytic stability. Therefore, designing efficient and stable catalysts for the SOR and exploring the inherent reaction mechanism are still formidable challenges. Herein, nickel foam-supporting Mo-doped Co3S4 nanosheet arrays (Mo-Co-S/NF) are synthesized and exhibit robust SOR catalytic activity and high long-term durability. The doped Mo species greatly improves the electronic structure of active sites and then enhances the intrinsic activity of the SOR. Mo-Co-S/NF only requires an ultra-low potential of 0.294 V vs. RHE to achieve a current density of 100 mA cm-2, which is significantly lower than that for the corresponding oxygen evolution reaction (OER, 1.610 V vs. RHE). What's more, Mo-Co-S/NF is further used to construct an asymmetric acid-base coupling electrolyzer based on the HER-SOR, which achieves simultaneous hydrogen and sulfur production with ultra-low energy consumption and can even generate extra electric energy at a low current density. This work provides unique insights into the design of SOR electrocatalysts and dissymmetrical electrolytes, providing more possibilities for green and low-cost hydrogen production. The doped Mo improves the SOR intrinsic activity of Co-based active sites in Mo-Co-S/NF; meanwhile, an advanced dissymmetrical acid-base-coupled electrolyzer is constructed to realize H2 and S8 production with low energy consumption.