Recent Progress in Nitrogen-Functionalized Carbon Materials for Supercapacitors: Synthesis, Properties, and Future...

Carbon materials are widely employed as electrode components in supercapacitors, where energy storage predominantly relies on the electrical double-layer (EDL) mechanism. However, the intrinsically limited energy density of EDL-based storage remains a major bottleneck in the development of high-performance supercapacitors. Introducing nitrogen-containing functional groups to impart pseudocapacitance has become a key strategy for enhancing specific capacitance. Despite significant progress, the fundamental roles of nitrogen functionalities in governing electrochemical behavior and overall electrode performance are not yet fully understood. This review systematically summarizes advances over the past decade in nitrogen-functionalized carbon materials for supercapacitor applications. This article systematically summarizes the classification, incorporation strategies, and characterization of various nitrogen species in carbon matrices, with a focus on their mechanistic roles in modifying structural, electronic, and physicochemical properties. We address the critical trade-off between high pseudocapacitance and electrical conductivity, proposing a semiquantitative model to identify an optimal doping range for balanced performance. A key contribution is the establishment of a closed-loop "material-preparation-characterization-performance" framework. Furthermore, we advocate for a "multi-technique integration coupled with theoretical validation" approach to achieve reliable structure-performance correlations. Finally, current challenges and future directions are outlined, providing guidance for the rational design of advanced carbon electrodes and next-generation energy storage devices.