Insight into high areal capacitances of low apparent surface area carbons derived from nitrogen-rich polymers

The energy storage mechanism of N-doped carbons with low apparent specific surface areas (Brunauer-Emmett-Teller specific surface area determined by N2 adsorption) has puzzled the researchers in the supercapacitor field in recent years. In order to explore this scientific problem, such carbon materials were prepared through pyrolysis of N-rich polymers such as melamine formaldehyde resin and polyaniline. Although these carbons possess low apparent specific surface areas of no more than 60 m2 g−1, their areal capacitance could reach up to an abnormally high value of 252 μF cm−2. The results of systematical materials characterizations and electrochemical measurements show that these carbons contain numerous ultramicropores which could not be detected by the adsorbate of N2 but are accessible to CO2 and electrolyte ions. These ultramicropores play dominant roles in the charge storage process for these low apparent surface area carbons, leading to an energy storage mechanism of electric double layer capacitance. The contribution of pseudocapacitance to the total capacitance is calculated to be less than 15%. This finding challenges the widely accepted viewpoint that the high capacitance of N-doped carbon is mainly attributed to the pseudocapacitance generated from the faradic reactions between nitrogen functionalities and electrolyte.