Nitrogen Doping Effects on the Physical and Chemical Properties of Mesoporous Carbons

Nitrogen-doped mesoporous carbons (NMCs) with controllable nitrogen doping and similar mesoporous structures are prepared by a facile colloidal silica nanocasting method using melamine, phenol, and formaldehyde as precursors. Various physicochemical properties, such as the oxidation stability, the conductivity and the electrochemical capacitive performance, the CO₂ adsorption, the basicity, and the metal-free catalytic activity of the NMCs, are studied extensively in relation to the incorporation amount of nitrogen in the carbon backbone. The dependence of the oxidation stability and the conductivity of the NMCs on the nitrogen content are similar; both of the biggest improvements are achieved at a low nitrogen content of ca. 4.2 wt %. While used as the supercapacitor electrodes, the NMCs with a mediate nitrogen content of ca. 8 wt % can take full advantage of the nitrogen-induced pseudocapacitance and the nitrogen-enhanced conductivity, delivering an excellent high-rate capacitive performance. The nitrogen content does not play an important role in the CO₂ physical adsorption, where the effect of microporosity prevails over the nitrogen-doped carbon surface. However, the nitrogen content determines the basicity of the NMCs, which governs their CO₂ chemical adsorption ability and the metal-free catalytic activity for direct oxidation of H₂S. The higher the nitrogen content, the higher the basicity and the catalytic activity. Our studies give a reliable relationship between nitrogen doping and the physicochemical properties of mesoporous carbons, which should provide a useful guide to their practical applications.