Electrochemical impedance of nitrogen-doped carbon with tunable mesoporous structure

Mesoporous nitrogen-doped carbon is a promising material in energy storage and conversion technologies, including efficient electrocatalyst supports. One of the effective techniques for producing mesoporous N-doped carbon is the sacrificial support method that provides a mesoporous structure with a narrow pore size distribution and easy control of the specific surface area. The method involves three stages: (i) mixing nitrogen-rich organic compounds used as a precursor and colloidal silica as a sacrificial agent; (ii) pyrolysis of the prepared mixture; (iii) chemical removal of sacrificial silica. In this work, we present, for the first time, a detailed electrochemical impedance spectroscopy (EIS) study of the mesoporous N-doped carbon obtained from methyl (2-benzimidazole) carbamate mixed with colloidal silica (10-40 wt.%). The frequency response, real and imaginary parts of the complex capacitance, as well as the Mott-Schottky plots measured at different a.c. frequencies have been analyzed. With 20-40 wt.% SiO₂ added to the precursor, the mesoporous N-doped carbon samples have been shown to behave in the electrolyte as an almost ideal capacitor due to the high homogeneity of interfaces in open, easy-to-access mesopores with a narrow pore size range. The frequency response is well described by a short equivalent circuit, with distinguishing between contributions made by surfaces of pores formed under removal of SiO₂ and those formed under pyrolysis of the precursor, which are charged consecutively. It has been shown that the parameters calculated from the Mott-Schottky analysis (flat band potential, linear dependence coefficient) are almost independent of the a.c. frequency, which also indicates high homogeneity of the carbon material in mesoporous matrix obtained by the sacrificial support method.