Effect of nitrogen doping on the surface properties of metal-free CMK-3 mesoporous carbons for catalytic and electrochemical applications

Nitrogen doping is a common strategy for improving the performance of carbon materials, but the specific role of N-containing functionalities often remains unclear owing to the interplay of multiple factors governing their behavior. In this study, model mesoporous CMK-3 carbons synthesized by nanoreplication of SBA-15 silica were used as a platform ensuring consistent porosity and degree of graphitization, while varying the content of N- and O-containing functional groups. CMK-3 replicas were prepared using sucrose and urea (at N/C ratios of 0, 0.14, and 0.51) and carbonized at 600–900 °C. With growing thermal treatment temperature, a slight increase in textural parameters, particularly microporosity, was observed. However, N species incorporation hindered this effect. Thermal analysis, Raman spectroscopy, XRD, elemental analysis, XPS, SEM-EDS and TEM studies confirmed a pronounced effect of higher carbonization temperature on the progressive ordering of graphitic domains and decomposition of N-containing functionalities with a preferential transformation of pyridinic groups into graphitic N species. No analogous trend was observed for O-containing functionalities, whose presence may originate both from precursor decomposition during carbonization and from post-synthetic surface oxidation upon exposure of the carbon surface to atmospheric air. As demonstrated by immersion calorimetry measurements, the presence of heteroatoms contributed to a reduction in hydrophobicity index, facilitating transport of polar molecules into the interior of material pores. Consequently, in catalytic oxidation of H 2 SO 3 in aqueous solution, superior performance was achieved for carbons with a higher degree of ordering of graphitic domains and containing nitrogen species that improve electronic properties of the carbon framework, as confirmed by CV and EIS.