Fabrication and electrochemical performance of Ni–Cu carbonate/hydroxide-based electrodes for high-performance supercapacitors

The increasing usage of high-performance equipment necessitates the exploration of new energy storage solutions. Supercapacitors offer significant advantages over secondary batteries, including longer lifespan, faster charge/discharge rates, higher power density, and greater reliability. Three-dimensional porous NiCu(CO₃)(OH)₂ nanowires were directly synthesized on Ni foam using a binder-free hydrothermal method as positive electrodes in high-performance supercapacitors. The unique nanowire structure of NiCu(CO₃)(OH)₂ plays a pivotal role in enhancing electrical performance by providing substantial surface area, improving electrode/electrolyte contact, and shortening ion diffusion paths. The use of Ni- and Cu-based binary transition metal electrodes contributes to high specific capacitance, rapid charge-discharge rates, and excellent cycling stability, collectively resulting in the development of high-capacity supercapacitors. Furthermore, density functional theory calculations were employed to elucidate the electrode formation energy based on the Ni/Cu ratio, assessing the structural stability of electrodes and offering insights for future energy storage device development. The optimized NiCu(CO₃)(OH)₂ nanowire compound exhibited an outstanding maximum specific capacity of 211.1 mAh g⁻¹ at 3 A g⁻¹. Furthermore, an asymmetric supercapacitor was constructed using the NiCu(CO₃)(OH)₂ composite as the positive electrode and graphene as the negative electrode. The resulting asymmetric supercapacitors demonstrate a remarkable energy density of 26.7 W h kg⁻¹ at a power density of 2534 W kg⁻¹, along with exceptional cycling stability, retaining 91.3% of its capacity after 5000 cycles. Consequently, the asymmetric supercapacitors incorporating NiCu(CO₃)(OH)₂ exhibit superior electrical properties compared to most previously reported Ni- and Cu-based asymmetric supercapacitors.