Space-Confined Synthesis of Lasagna-like N-Doped Graphene-Wrapped Copper-Cobalt Sulfides as Efficient and Durable Electrocatalysts for Oxygen Reduction and Oxygen Evolution Reactions

Searching for efficient and economical bifunctional oxygen electrocatalysts is urgent for exploring sustainable energy technologies. Herein, the unique lasagna-like structured copper-cobalt sulfides wrapped with N-doped reduced graphene oxide (CuCoS/N-rGO) were first fabricated through in situ controllable growth of bimetallic metal-organic frameworks (CuCo-BTC) on GO followed by further pyrolysis and sulfuration. The interconnected structure was formed because the bimetallic ions and carboxyl groups in the CuCo-BTC precursor combine with the functional groups (-COOH, -OH, etc.) on the surface of GO to interconnect the graphene sheets to avoid agglomeration of subsequent pyrolysis. In turn, the carbonized graphene was used as a space-constrained reactor to wrap CuCoS particles to prevent their aggregation and the electronic distribution changed between them to produce an excellent synergistic effect. In the exploration of the molar ratios of bimetallic ions, the optimal CuCoS-4/N-rGO with n(Co)/n(Cu) of 4:1 possessed a unique structure, a larger specific surface area (150 m(2) g(-1)), and splendid electrocatalytic activity, with the highest onset potential of 0.97 V (vs reversible hydrogen electrode, RHE), the largest limiting current density of 5.2 mA cm(-), outstanding durability toward the oxygen reduction reaction, and the smallest overpotential of 288 mV (vs RHE) at 10 mA cm(-2) toward the oxygen evolution reaction. Furthermore, lasagna-like CuCoS-4/N-rGO also showed satisfactory power density (143.2 mW cm(-2)) and prominent rechargeable ability compared with Pt/C when assembled in Zn-air batteries.