Nitrogen-enriched carbon electrodes in electrochemical capacitors: investigating accessible porosity using CM-SANS

Carbon electrochemical capacitor electrodes containing nitrogen groups were studied with respect to their electrochemical behaviour, chemical composition and physical characteristics. Thermal treatment of nitrogen-enriched carbon materials in different atmospheres was used to control the specific type and concentration of nitrogen groups present, while importantly retaining similar pore size distributions. Pyridinic nitrogen is shown to be most likely responsible for increased values of surface area normalized specific capacitance, although the mechanisms by which this occurs are poorly understood. Contrast matched-small angle neutron scattering (CM-SANS) was employed to probe the electrode porosity accessible to an electrolyte and indicates that there is no appreciable difference between the materials studied. Cyclic Voltammetry showed no evidence of electrode reactions occurring over the operating potential range. Therefore a greater amount of charge is displaced at pyridinic sites during the charge-discharge process. This may occur due to a specific adsorption mechanism, coupled with enhanced electron conductivity through the carbon matrix.