Facile synthesis of binary transition metal sulfide tubes derived from NiCo-MOF-74 for high performance supercapacitors

Recently, binary transition metal oxides, phosphates, and sulfides have attracted wide attention due to their potential applications in supercapacitors. The emergence of metal-organic frameworks (MOFs) provides new opportunities for the synthesis and investigation of porous binary metal compounds with similar microstructures. Herein, binary metal oxide (NiCo-O) tubular structures are derived from NiCo-MOF-74 via a facile annealing process, and then phosphate (NiCo-P) and sulfide (NiCo-S) structures are obtained from NiCo-O by heat treatment and solvothermal process, respectively. Among the three derivatives, NiCo-S with nanosheet structures has the highest specific capacitance of 930.4 F g(-1) at a current density of 1 A g(-1) and an excellent rate capability with a retention of approximate to 80% at 10 A g(-1). The long-term cycling performance of NiCo-S is superior with 70.5% retention after 10 000 cycles. The hybrid supercapacitor device with NiCo-S and activated carbon as positive and negative electrodes delivers a high energy density of 22.6 W h kg(-1) at a power density of 800 W kg(-1). The excellent performance of NiCo-S can be attributed to its nanosheet structure, which increases the specific surface area and electroactive sites.