Significantly improved conductivity of spinel Co3O4 porous nanowires partially substituted by Sn in tetrahedral sites for high-performance quasi-solid-state supercapacitors†
Porous spinel-structured Co3O4 nanowires partially substituted by Sn in tetrahedral sites (CSO) were grown on a multi-layered graphene film (CSO@GF) with a high specific surface area (SSA) through a simple and low-cost hydrothermal method, followed by a thermal annealing process. The as-synthesized binder-free CSO@GF electrode exhibited high specific capacitance (2032.6 F g−1 at 1 A g−1), superior rate capability (approximately 55.1% capacitance retention even at a current density of up to 40 A g−1), and remarkable cycling stability (94.3% capacitance retention after 10 000 cycles) due to significantly improved conductivity, which was further verified by density functional (DFT) calculations. A quasi-solid-state asymmetric supercapacitor (ASC) composed of the prepared CSO@GF and Fe2O3@GF as the positive and negative electrodes, respectively, was fabricated using a PVA-KOH gel electrolyte. The as-assembled supercapacitor delivered a prominent specific capacitance of 200.2 F g−1, an outstanding energy density of 62.6 W h kg−1 at a power density of 751.2 W kg−1, and an excellent cycling stability with 91.69% capacity retention after 10 000 cycles, suggesting great potential for CSO@GF in high energy density storage devices.