Interface Engineering of Hollow CoO/Co4S3@CoO/Co4S3 Heterojunction for Highly Stable and Efficient Electrocatalytic Overall Water Splitting

The key to improve the performance of electrochemically water splitting and simplify the entire system is to develop a dual-functional catalyst, which can be applied to catalyze the process of HER and OER. Therefore, we synthesized a novel hollow CoO/Co 4 S 3 @CoO/Co 4 S 3 heterojunction with a core–shell structure as an excellent dual-functional catalyst. This sample is composed of an outer hollow CoO/Co 4 S 3 cubic thin shell and an inner hollow CoO/Co 4 S 3 sphere, and it can provide abundant catalytic active sites while effectively promoting the flow of reactants, products, and electrolytes. Meanwhile, the O–Co–S bond in the heterojunction interface can promote both the CoO active site in OER and theCo 4 S 3 active site in HER. Therefore, the overpotential of the hollow CoO/Co 4 S 3 @CoO/Co 4 S 3 is only 190 mV (OER) and 81 mV (HER), respectively, at the current density of 10 mA cm –2 . Moreover, the hollow CoO/Co 4 S 3 @CoO/Co 4 S 3 showed the outstanding electrochemical stability in 60 h. In addition, in the two-electrode system assembled from the hollow CoO/Co 4 S 3 @CoO/Co 4 S 3, only the potential of 1.48 V can achieve the current density of 10 mA cm –2 . Impressively, the commercial solar panel is sufficient to drive the two-electrode electrolyzer consisting of hollow CoO/Co 4 S 3 @CoO/Co 4 S 3 . This finding offers a promising nonprecious metal-based catalyst that can be applied to catalyze the electrochemical overall water splitting.