Defect engineering in carbon skeletons toward precise edge-nitrogen doping for efficient electrochemical energy storage

Abstract

The development of high-performance carbon materials for electrochemical energy storage has relied on precise control over atomic configurations. However, conventional nitrogen-doping methods typically produced random dopant distributions and mixed configurations, which limited the improvement of electrochemical activity. In this work, we demonstrated that structural defects intrinsically directed the selective incorporation of highly active nitrogen atoms at edge sites of the carbon skeleton, achieving defect-induced precise edge-N (N-5 and N-6) doping. High-power ultrasonication introduced numerous structural defects, mainly new zigzag edges, into the two-dimensional graphene lattice. Multi-scale analyses, from bulk spectroscopies (XPS, EPR) to atomic-resolution EELS mapping, demonstrated that N atoms were concentrated at edge regions, predominantly forming edge-N configurations with the π*/σ* ratio nearly 10 times higher than that of the in-plane region. By analyzing the N doping process (up to 600 °C), it was found that the healing of carbon structure defects was limited within this temperature range. These defect sites exhibited stronger adsorption toward NH₃ than the basal plane proved by density functional theory (DFT) calculations as the energetic basis, and NH₃ indeed preferentially attacked defect sites passivated by H or O-containing groups. Consequently, the abundant and persistent defects under 600 °C as active sites led to a gradual increase in total nitrogen content while maintaining a high and stable proportion of edge-N (∼72%). When the temperature exceeded 600 °C, both the overall nitrogen content and the proportion of edge-N decreased. The defect-engineered graphene (sN-C-600) exhibited a 116.8% increase in specific capacitance relative to its undoped counterpart and delivered a 24.9% higher capacitance than the non-defect sample (LN-C-600). Overall, this study established structural defects as active regulators of N heteroatom incorporation, providing design guidance for constructing carbon electrodes with controllable edge chemistry and optimized electrochemical functionality.