Significantly improved conductivity of spinel Co₃O₄porous nanowires partially substituted by Sn in tetrahedral sites for high-performance quasi-solid-state supercapacitors

Porous spinel-structured Co₃O₄nanowires 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⁻¹at 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⁻¹at 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.