Nitrogen enriched porous carbon spheres: attractive materials for supercapacitor electrodes and CO2 adsorption
A series of nitrogen-containing polymer and carbon spheres were obtained by the sol-gel method. In particular, the nitrogen-rich carbon spheres were prepared by one-pot hydrothermal synthesis in the presence of resorcinol/formaldehyde as carbon precursors and ethylenediamine (EDA) as both a base catalyst and nitrogen precursor, followed by carbonization in nitrogen and activation with CO2. The introduction of EDA to the sol-gel system resulted in structurally bonded nitrogen-containing carbon spheres. The nitrogen doping level and the particle size can be tuned by varying the EDA amount in the reaction mixture. The maximum nitrogen doping level of 7.2 wt % in carbon spheres could be achieved without sacrificing the spherical morphology. The diameter of these carbon spheres (CS) can be tuned in the rage of 50-1200 nm by varying the EDA amount. N2 adsorption analysis showed that the aforementioned activated carbon spheres exhibited high surface area reaching up to1224 m2/g. Ultra high CO2 adsorption capacities, 4.1 and 6.2 mmol/g, corresponding to an equilibrium pressure of 1 bar, were measured on nitrogen-containing activated carbon spheres at 25 and 0 °C, respectively. Electrochemical measurements performed on these carbon spheres for double layer capacitors showed very high capacitance up to 388 F/g at 1.0 A/g, outstanding rate capability (60% capacitance retention at 100 A/g), and unprecedented cycling stability (98% capacitance retention even after 8000 cycles) in 1 M H2SO4 electrolyte solution.