Ultramicroporous Carbon Nanoparticles for the High-Performance Electrical Double-Layer Capacitor Electrode

Novel ultramicroporous carbon nanoparticles (UCNs) are synthesized on the basis of solvothermal polymerization of phloroglucinol and terephthaldehyde in dioxane at 220 °C, followed by carbonization at 850 °C. The resultant UCNs show regular 0.54 nm ultramicropores and particle sizes of ∼30 nm. The UCNs as electrode materials for electrical double-layer capacitors (EDLCs) show a specific capacitance of 206 F g –1 at 1.0 A g –1 in a 6 M KOH aqueous solution. The UCN electrode is suitable for charge–discharge operation even at a very high current density of 50 A g –1 coupled with a capacitance of 135 F g –1, indicating excellent high-rate electrochemical performance. The electrochemical capacitance of the UCN electrode has a high retention of 97.6% after 5000 cycles at 1.0 A g –1 tested by a standard three-electrode system (97.3% for the two-electrode cell), which implies a good electrochemical cycling life. This study highlights promising prospects of novel UCNs as advanced electrode materials for EDLCs where a high level of current charge and discharge is required.