One-pot synthesis of hierarchical porous carbons with extended ultramicropores: New prospective materials for supercapacitors

•One pot synthesis from 4:1 ratio of melamine/formaldehyde+resorcinol in basic medium.•The pyrolysis temperature determines textural properties and chemical composition.•All carbons showed a predominant electrical double layer capacitive behaviour.•Best specific capacitance and capacitance retention if pyrolysis at 800 °C and above.•Excellent cycling over 10,000 cycles, coulombic efficiency slightly above 100 %. A series of carbon electrodes was synthesized via a modification of the polymerization-condensation reaction, where a 4:1 mass excess of melamine was added in basic media to the resorcinol/formaldehyde classical mixture. Melamine, together with variations of the pyrolysis temperature play a key role to define the chemical and textural properties of these carbons. A high nitrogen content, ranging from 23.2 to 11.3 % was determined. A low degree of crystallinity and disordered internal structure were assessed, while a hierarchical porous structure was stablished for all samples, including an important ultramicroporosity, with pore sizes below 0.7 nm. All electrodes showed a predominant double layer capacitive behaviour in aqueous H2SO4, while a small pseudocapacitive contribution was also evidenced for the three carbons pyrolysed at higher temperatures. These three electrodes show the highest specific capacitance (maximum of 153.6 F g−1), and outstanding cycling over 10,000 cycles. A comprehensive analysis correlating morphological and surface properties and the electrochemical behaviour was carried out. The best performing carbon was selected to construct a symmetrical device for which a specific capacitance of 103 F g−1 was determined, reaching energy and power density values of 1.4 Wh Kg−1 and 111.7 W Kg−1, respectively. [Display omitted]