Metal-Organic Framework-Derived Nickel-Cobalt Sulfide on Ultrathin Mxene Nanosheets for Electrocatalytic Oxygen Evolution.

Water oxidation is the key process for many sustainable energy technologies containing artificial photosynthesis and metal-air batteries. Engineering inexpensive yet active electrocatalysts for water oxidation is mandatory for the cost-effective generation of solar fuels. Herein, we propose a novel hierarchical porous Ni-Co-mixed metal sulfide (denoted as NiCoS) on TiCT MXene via a metal-organic framework (MOF)-based approach. Benefiting from the unique structure and strong interfacial interaction between NiCoS and TiCT sheets, the hybrid guarantees an enhanced active surface area with prominent charge-transfer conductivity and thus a superior activity toward oxygen evolution reactions (OERs). Impressively, the hierarchical NiCoS in the hybrid is converted to nickel/cobalt oxyhydroxide-NiCoS assembly (denoted as NiCoOOH-NiCoS) by OER measurement, where NiCoOOH on the surface is confirmed as the intrinsic active species for the consequent water oxidation. The hybrid material is further applied to an air cathode for a rechargeable zinc-air battery, which exhibits low charging/discharging overpotential and long-term stability. Our work underscores the tuned structure and electrocatalytic OER performance of MOF derivatives by the versatility of MXenes and provides insight into the structure-activity relationship for noble metal-free catalysts.