High-energy X-ray irradiation-induced functionalization of Ni(OH)₂ for enhanced supercapacitor electrodes

Nickel hydroxide (Ni(OH)₂) is a promising electrode material for supercapacitors due to its high theoretical capacitance. However, its practical performance is hindered by limited cycle stability, poor electrical conductivity, and sluggish ion transport. To overcome these limitations, this study introduces a novel strategy involving high-energy X-ray irradiation-induced functionalization to enhance the electrochemical properties of Ni(OH)₂ electrodes. Pristine Ni(OH)₂ was subjected to 15 MV X-ray irradiation at a dose of 10-20 Gy, utilizing Compton scattering to induce controlled surface-level modifications while preserving the bulk crystal structure. Physicochemical characterizations including XRD, Raman spectroscopy, FTIR, and ICP-MS revealed the introduction of new surface functionalities and optimized ion diffusion pathways, without compromising isotopic or crystallographic integrity. Electrochemical performance was evaluated in 1.0 M Na₂SO₄ electrolyte. The irradiated electrode (f-Ni(OH)₂) demonstrated a specific areal capacitance of 671.2 mF·cm⁻² at a scan rate of 1 mV·s⁻¹, marking a 41% improvement over its non-irradiated counterpart (474.7 mF·cm⁻²). Galvanostatic charge-discharge measurements yielded a high capacitance of 1253.5 mF·cm⁻² at 1.0 mA·cm⁻². Electrochemical impedance spectroscopy further confirmed enhanced ion and electron kinetics, with a decrease in solution resistance from 18.4 Ω to 13.0 Ω. Critically, the f-Ni(OH)₂ electrodes retained 99.2% of their initial capacitance after 5,000 continuous cycles, demonstrating exceptional long-term stability. The observed improvements place f-Ni(OH)₂ within the performance range of microsupercapacitor technologies, highlighting their strong potential for future integration into miniaturized energy storage platforms. This work represents the first demonstration of using high-energy X-ray irradiation to functionalize metal hydroxides for energy storage applications, offering a scalable, chemical-free, and cost-effective approach to engineer next-generation supercapacitor electrodes. The findings provide new insights into radiation-matter interactions for material engineering, offering a promising route toward high-performance, long-lifespan energy storage systems.