Abstract: With the surge of demand for instant high power in miniaturized electronic and mechanical systems, supercapacitors (SCs) are considered as one of the viable candidates to fulfill the requirements. Thus, long-term resilience and superior energy density associated with self-discharge in SCs are obviously critical, but securing electrode materials, which can meet both benefits of SCs and persist charged potential for a comparatively prolonged duration, are still elusive. Herein, hierarchically refined nickel-sulfide heterostructure (CuO-NS) on CuO (CO) scaffold is achieved through optimized film formation, exhibiting a threefold improvement in the essential electrochemical characteristics and outstanding capacitance retention (∼5% loss). Self-discharge behavior and its mechanism are systematically investigated via morphological control and nanostructural evolution. Furthermore, significant mitigation of self-discharge owing to an increase in surface area and refined nanostructure is displayed. Remarkably, CuO-NS2 (20 cycle overcoating) based SC can retain over 60% of the charged potential for a complete voltage holding and a self-discharge test for 16 h. An appealing demonstration of wireless power transmission in burst mode is demonstrated for secure digital (SD) card data writing, powered by SCs, which substantiates that it can be readily leveraged in power management systems. This enables us to realize one of the envisioned applications soon.

Key words: CuO-Ni₃S₂ hierarchical heterostructure, Voltage holding test, Supercapacitor, Self-discharge mitigation, Wireless power transmission