Three‐Dimensional Hierarchically Mesoporous ZnCo 2 O 4 Nanowires Grown on Graphene/Sponge Foam for High‐Performance, Flexible, All‐Solid‐State Supercapacitors

To achieve high energy storage on three‐dimensional (3D) structures at low cost, materials with high power and long cycle life characteristics have to be developed. We synthesized ZnCo 2 O 4 /reduced graphene oxide (rGO) binary composites in commercial sponges. ZnCo 2 O 4 nanosheets were grown on the surface of GO/sponge through a hydrothermal reaction. The resulting flexible, free‐standing ZnCo 2 O 4 /rGO/sponge electrodes were used as the electrodes in a symmetric supercapacitor. ZnCo 2 O 4 /rGO/sponge electrodes have a large specific capacitance of 1116.6 F g −1 at a scan rate of 2 mV s −1 in aqueous electrolyte. The all‐solid‐state flexible supercapacitor is assembled based on ZnCo 2 O 4 /rGO/sponge electrodes, which show excellent electrochemical performances with a specific capacitance of 143 F g −1 at a current density of 1 A g −1 . The as‐fabricated supercapacitor also exhibits excellent cycling stability (93.4 % capacitance retention after 5000 cycles) and exceptional mechanical flexibility. These results demonstrate the potential of ZnCo 2 O 4 /rGO/sponge as an electrode in flexible, high‐performance supercapacitors.