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 Ti3C2Tx MXene via a metal–organic framework (MOF)-based approach. Benefiting from the unique structure and strong interfacial interaction between NiCoS and Ti3C2Tx 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