Tuning morphology and conductivity in two-step synthesis of zinc-cobalt oxide and sulfide hybrid nanoclusters as highly-performed electrodes for hybrid supercapacitors

Abstract

We reported a facile two-step hydrothermal procedure to prepare zinc-cobalt oxide and sulfide hybrid nanoclusters (ZCOSH NCs), initialized by the synthesis of metal oxides and followed by the partial substitution of oxygen with sulfur. Benefiting from their morphological features and partial substitution with sulfur, both the electrical conductivity and further the actual specific capacitance of ZCOSH NCs were apparently improved compared to zinc-cobalt binary oxide nanosheets (ZCO NSs). Moreover, its cycling stability has also been significantly enhanced. Its excellent specific capacitance achieved 2176.7 F g−1 at 1 A g−1, which was six times larger than ZCO NSs (367.2 F g−1 at 1 A g−1). Moreover, a hybrid supercapacitor was assembled using ZCOSH NCs as its positive electrode and the activated carbon as its negative electrode. This hybrid supercapacitor device presented a higher specific capacitance value of 116.3 F g−1 at 1 A g−1 with corresponding specific energy of 41.4 W h kg−1 at a specific power of 801.3 W kg−1, and a superior cycling stability after 3000 charge-discharge cycling tests. This study confirmed the feasible and unique synthesis approach to balance the higher capacitance of oxides and the higher electric conductivity of sulfides within this binary ZCOSH NC.