Interfacial Modulation of Nickel Tungstate by Polyethylene Glycol Toward Enhanced Electrochemical Energy Storage

Tailoring electrochemically favorable architectures through polymer-assisted growth regulation offers an effective route for overcoming the structural limitations that restrict the practical performance of pseudocapacitive materials. In this study, a polyethylene glycol (PEG)-mediated interfacial modulation strategy was developed to regulate the structural evolution and electrochemical behavior of hydrothermally synthesized nickel tungstate (NiWO4) for asymmetric supercapacitor applications. The influence of PEG concentration (0.1, 0.3, and 0.5 wt%) on crystal growth, morphology evolution, and charge-storage characteristics was systematically investigated. Structural analysis confirmed the successful formation of phase-pure monoclinic NiWO4 without detectable impurities, while morphological studies revealed a pronounced PEG-dependent transformation in surface architecture. Among all synthesized electrodes, the optimized NiWO-P3 sample exhibited a highly interconnected porous nanograin framework with improved structural homogeneity and abundant electrochemically accessible interfaces. This favorable morphology significantly facilitated electrolyte penetration, accelerated ion transport, and enhanced redox utilization. Consequently, NiWO-P3 delivered a superior areal capacitance of 9.284 F/cm2 at 10 mA/cm2 and retained nearly 84% capacitance at elevated current density, demonstrating excellent rate capability. The optimized electrode further exhibited enhanced diffusion kinetics, achieving anodic and cathodic diffusion coefficients of 21.26 × 10−7 and 10.55 × 10−7 cm2/s, respectively, along with remarkable cycling durability of 85.12% after 12,000 cycles. Furthermore, the fabricated NiWO-P3//AC asymmetric supercapacitor demonstrated (ASD) promising electrochemical reversibility and prolonged operational stability, highlighting PEG-assisted interfacial engineering as an effective strategy for advancing high-performance tungstate-based energy-storage materials.