3D flower-like oxygen-deficient non-stoichiometry zinc cobaltite for high performance hybrid supercapacitors

Non-stoichiometry and defect engineering of nanostructured materials plays a vital role in controlling the electronic structure, which results in enhancing the electrochemical performances. Herein, we report three-dimensional (3D) oxygen-deficient flower-like non-stoichiometry zinc cobaltite (Zn_1.5Co_1.5O_4−δ) for hybrid supercapacitor applications. In particular, XRD, XPS and Raman analyses confirm the oxygen-deficiency of the non-stoichiometry Zn_1.5Co_1.5O_4−δ. The oxygen-deficient non-stoichiometry and 3D hierarchical porous structure of Zn_1.5Co_1.5O_4−δ offer the efficient utilization of abundant electrochemical active sites and the rapid transportation of ion/electron. Accordingly, the Zn_1.5Co_1.5O_4−δ electrode achieves the high specific capacitance of 763.32 F g⁻¹ at 1 A g⁻¹, which is superior to those of ZnCo₂O₄ (613.14 F g⁻1), Co₃O₄ (353.88 F g⁻¹) and ZnO (248.59 F g⁻¹). The hybrid supercapacitor cells, configuring Zn_1.5Co_1.5O_4−δ as the positive electrode and activated carbon as negative electrodes, respectively, deliver the maximum energy/power densities (40.49 W h kg⁻¹ at 397.37 W kg⁻¹ and 20.87 W h kg⁻¹ at 50.08 kW kg⁻¹) and outstanding cycle stability with capacitance retention of 89.42% over 20 000 cycles.