Distorted Inverse Spinel Nickel Cobaltite Grown on a MoS2 Plate for Significantly Improved Water Splitting Activity

Sluggish water dissociation kinetics on nonprecious metal oxide electrocatalysts is considered as the rate-limiting step for the development of hydrogen evolution in alkaline media. A unique heterostructure, a distorted inverse spinel Ni-Co-O layer on MoS2 plate, was developed in this paper. The formation of Mo-O-Co covalent bonds at the interface allows for the inherent electron transfer from MoS2 to the adjacent surface spinel and forces the nucleation and creation of disordered inverse spinel. Such a crystal-distorted structure enables the substantially improved activity for hydrogen evolution reaction (HER) by more than 40 times and oxygen evolution reaction (OER) by 2.5 times compared to the regular spinel nickel cobaltite. Through a comprehensive kinetics study, the results reveal that this inverse spinel layer promotes the water dissociation process and the intrinsic HER activity by decreasing the apparent activation energy barrier E-a, increasing the exchange current density j(0), and improving the charge-transfer rate. Meanwhile, the oxygen vacancy-mediated Ni3+ active center and the facilitated charge transfer are responsible for OER activity improvement. Such a unique heterostructure demonstrates robust stability for HER, OER, and overall water splitting in alkaline electrolytes. Our work provides a novel concept to design effective metal oxide-based HER and OER catalysts in alkaline electrolyte.