Preparation, surface characteristics, and electrochemical double-layer capacitance of KOH-activated carbon aerogels and their O- and N-doped derivatives

► Carbon aerogels are KOH-activated at various weight ratios to increase their porosity. ► Oxygen and nitrogen functionalities are introduced by different surface treatments. ► The gravimetric capacitance is related to N2 adsorption-measured microporosity. ► The gravimetric capacitance linearly decreases with increasing particle density. ► A volumetric capacitance as high as 123 F cm−3 is obtained with an O-doped carbon.