One-pot in situ solvothermal synthesis of ZnCo2S4/carbon nanosphere composites: tuning carbon content for high-performance supercapacitor electrodes

Abstract

The impact of in situ carbon loading in the binary transition metal sulphide-based nanocomposites for designing high-performance supercapacitor electrodes requires a comprehensive investigation. In this work, a series of nanostructured materials—including pristine ZnCo2S4, carbonaceous nanospheres (CNS), and a set of dextrose-derived ZnCo2S4/CNS nanocomposites (labelled as ZnCo2S4/CNS (Dx), where 'x' denotes the mole ratio of dextrose (D) to Zn precursor and takes values of 1, 2, 5, and 10) was synthesized via a facile, one-pot, in situ solvothermal route. Notably, the ZnCo2S4/CNS (D2) nanocomposite exhibited heterogeneous and porous nano/microsphere morphology with efficient integration of ZnCo2S4 and CNS. In three-electrode supercapacitor studies at 1 A g—1 using 3 M KOH, the ZnCo2S4/CNS (D2) electrode demonstrated superior specific capacitance of 1462 F g—1 related to ZnCo2S4 (768 F g—1), CNS (75 F g—1), and ZnCo2S4/CNS (D1, D5 and D10) nanocomposites (546-1164 F g—1), with maintaining 75% of capacitance upto 5000 cycles. Remarkably, in different two-electrode configurations at 1 A g—1 in 3 M KOH, the ZnCo2S4/CNS (D2) electrode showed a doubled specific capacitance of 227 F g—1 for the symmetric supercapacitor, while a doubled energy density of 16.8 W h kg—1 with comparable power density of 533 W kg—1 for the asymmetric supercapacitor. The exceptional supercapacitor performance of ZnCo2S4/CNS (D2) nanocomposite could be attributed to the efficient synergistic interaction between ZnCo2S4 and carbon within this optimized composition, which enhances its structural and electrical characteristics for more availability of electroactive redox sites, better electrode-electrolyte affinity, and efficient electron/ion transport properties, thereby increasing charge storage capacity. Therefore, rational in situ solvothermal synthesis of optimal CNS-loaded bimetallic sulfide using different precursor materials will be a promising strategy to achieve high-performance electrode materials for supercapacitor electrodes in the future.