The relationship between the high-frequency performance of supercapacitors and the type of doped nitrogen in the carbon electrode

• Pyrrolic N enhances charge storage capacity at high frequencies due to higher adsorption energy. • Graphitic N improves ion response speed at high frequencies due to lower adsorption energy. • Adsorption energy is proposed as a universal descriptor for designing high-frequency supercapacitor electrodes. • Gradient carbonization of melamine foam enables controlled surface N configurations for optimized performance.