Polyvinylpyrrolidone-Functionalized NiCoO Electrodes for Advanced Asymmetric Supercapacitor Application.

Designing advanced electrode architectures with tailored morphology and redox synergy is essential for achieving high-performance supercapacitive energy storage. In this study, a PVP-assisted hydrothermal approach was employed to synthesize binder-free NiCoO nanostructured electrodes directly on nickel foam substrates. By modulating the PVP concentration (0.5-2 wt%), hierarchical flower-like nanosheets were engineered, with the NiCo-P sample (1 wt% PVP) exhibiting an optimized structure, superior electroactive surface area, and enhanced ion accessibility. Comprehensive electrochemical analysis revealed that NiCo-P delivered an outstanding areal capacitance of 36.5 F/cm at 10 mA/cm, along with excellent cycling stability over 15,000 cycles with 80.97% retention. Kinetic studies confirmed dominant diffusion-controlled redox behavior with high OH diffusion coefficients and minimal polarization. An asymmetric pouch-type supercapacitor device (NiCo-P//AC) exhibited a wide operating window of 1.5 V, achieving a remarkable areal capacitance of 187 mF/cm, energy density of 0.058 mWh/cm, and capacitive retention of 78.78% after 5000 cycles. The superior performance is attributed to the synergistic integration of mixed-valence Ni and Co species, engineered nanosheet morphology, and low interfacial resistance. This work underscores the significance of surfactant-directed design in advancing cost-effective, high-performance electrodes for next-generation flexible energy storage technologies.