Voltage holding and self-discharge phenomenon in ZnO-Co₃O₄ core-shell heterostructure for binder-free symmetric supercapacitors

We report an eco-friendly, in-situ, and one-step synthesis of ZnO-Co₃O₄ core-shell heterostructure (ZC-CSH) using the hydrothermal process as a transcendent nanomaterial for the supercapacitor applications. The ZC-CSH SSC showed a wide potential window (1.6 V), the excellent specific capacitance of 177.0F g⁻¹ at 1.4 A g⁻¹, high energy density (39.3 W h kg⁻¹), and power density (19064.3 W kg⁻¹). Further, the ZC-CSH SSC revealed excellent stability of 92.8 % after 10,000 cycles at 12.4 A g⁻¹ using galvanostatic charging-discharging. Besides, the ZC-CSH SSC unraveled the outstanding stability of 96.1 % after the 8 h Voltage holding tests (VHT) at 1.6 V + 8 h Self-discharge tests (SDT). Moreover, the ZC-CSH SSC indicated a trivial leakage current of 0.06, 0.11, 0.15, and 0.17 mA during 2, 4, 6, and 8 h VHT, respectively. The ZC-CSH SSC demonstrated a voltage drop from 1.6 V to 0.39, 0.38, 0.37, and 0.36 V after 2, 4, 6, and 8 h VHT and SDT. To understand the ZC-CSH SSC's self-discharge behavior, this work explored the insights of the self-discharge mechanisms based on two thermodynamic processes, ionic concentration gradient (diffusion-control model) and potential difference (potential-driven model). Also, according to the tight-bonding (strong interactions) and loose-bonding (weak interactions), this work envisaged electrolyte ions' interactions with electrode materials to explore the coherent insights of the self-discharge behavior of the ZC-CSH SSC. It is concluded that this approach can lead to an unwavering performance of the ZC-CSH SSC for electronic portable futuristic gadgets.