Impact of nitrogen doping on charge storage and self-discharge behaviour of zinc ion hybrid supercapacitor

Abstract

Zinc-ion hybrid supercapacitors (ZHSCs) offer a compelling balance of high energy and power densities, safety, and cost-effectiveness, making them attractive for sustainable energy storage applications. However, the limited specific capacitance of conventional carbon cathodes restricts their compatibility with high-capacity Zn anodes, leading to suboptimal performance. Nitrogen doping in carbon materials emerges as a promising approach to address this limitation by enhancing electrochemical properties. In this study, nitrogen-doped carbon materials are synthesized using varying urea precursor concentrations to systematically evaluate their impact on specific capacitance, cycling stability, coulombic efficiency, and self-discharge behaviour. Optimized doping achieves a 2.4-fold improvement in specific capacitance (268 F g⁻¹ at 1 A g⁻¹) and 97 % cycling retention, compared to undoped carbon (111 F g⁻¹ at 1 A g⁻¹). A detailed self-discharge analysis reveals significant suppression of leakage current (9.4-fold reduction) and an 18.3 % lower OCV decay over 300,000 s, attributed to higher pyridinic and graphitic nitrogen content. By deconvoluting ohmic, redistribution, and faradaic contributions, the role of nitrogen doping in mitigating self-discharge is clarified. These results underscore the potential of nitrogen-doped carbons to advance ZHSCs, paving the way for their implementation in high-performance and sustainable energy storage solutions.