<scp>3D</scp> 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 (Zn1.5Co1.5O4−δ) for hybrid supercapacitor applications. In particular, XRD, XPS and Raman analyses confirm the oxygen-deficiency of the non-stoichiometry Zn1.5Co1.5O4−δ. The oxygen-deficient non-stoichiometry and 3D hierarchical porous structure of Zn1.5Co1.5O4−δ offer the efficient utilization of abundant electrochemical active sites and the rapid transportation of ion/electron. Accordingly, the Zn1.5Co1.5O4−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 Zn1.5Co1.5O4−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.

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