B/P-Codoped Porous Carbon Electrode for Supercapacitors with Ultrahigh Energy Density

A series of B-, P-, and B/P-codoped carbon samples have been synthesized by carbonization of a phloroglucinol-salicylaldehyde-melamine (PSM@silica)-based polymer/silica composite under a nitrogen environment at 900 °C. Carbonization of PSM@silica under identical conditions and without any external doping has been reported previously by our group (Pal, A.; ACS Appl. Energy Mater. 2021, 4, 10810–10825) to yield N/O-doped spherical carbon particles (CPSM-900) with remarkable electrochemical properties. In order to investigate the effect of heteroatom doping from an external source, PSM@silica has been mixed with H3BO3, (NH4)2HPO4, or H3BO3/(NH4)2HPO4 in different amounts to obtain the doped materials. Further, 1.5 mmol H3BO3 (CPSM-1.5B) or (NH4)2HPO4 (CPSM-1.5P) or a mixture of 0.75 mmol H3BO3/0.75 mmol (NH4)2HPO4 (CPSM-0.75B/0.75P) afforded the best materials where the heteroatom content increased from CPSM-1.5B (7.0%) to CPSM-1.5P (11.0%) to CPSM-0.75B/0.75P (13.9%). The doped samples retain spherical morphology and a high surface area, as does CPSM-900 without any external doping. However, a drastic enhancement is observed in the electrochemical properties of the doped samples, which parallels the heteroatom content. The specific capacitance of CPSM-0.75B/0.75P reaches 1046 F/g at a current density of 0.6 A/g in 1 M H2SO4 (which is 400 F/g for CPSM-900) with very high power (270 W/kg) and energy density (118 Wh/kg) values, thereby bridging the gap between conventional supercapacitors and batteries. It has been illustrated that a symmetric device constructed with the material can illuminate a green light-emitting diode (LED) bulb of 3 V, and it can be recharged and reused indicating its sustainable energy-storage capability.