Nitrogen-phosphorous co-doped porous carbon from cross-linked polymers for supercapacitor applications

Abstract

Herein, we report co-doped porous carbon with nitrogen-phosphorous derived from cross-linked polyvinyl alcohol and polyvinylpyrrolidone (AC-PA/PP/AP-x) polymers synthesized using a simple single activation process. Diammonium hydrogen phosphate (AP) acting as nitrogen and phosphorous source was used to dope the cross-linked polymer precursors. The properties of the as synthesized carbon materials were analysed using the following techniques: scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDS) mapping, Raman spectroscopy and nitrogen sorption isotherm. The optimized AC-PA/PP/AP-0.5 sample possess the highest porous surface properties i.e., specific surface area (2656 m2g−1), pore volume (1.08 cm3g−1) and micropore volume (0.99 cm3g−1). The sample also achieved a remarkable specific capacitance (252Fg−1) corresponding to a specific current of 1Ag−1measured within the presence of 2.5 M KNO3 aqueous electrolyte, in three electrode set-up. The constructed symmetric AC-PA/PP/AP-0.5//AC-PA/PP/AP-0.5 SC with a good electrical series resistance (ESR = 0.6 Ω), delivers a great specific energy (27.3 W h kg-1) and specific power (400 W kg-1) when monitoring at 0.5Ag−1using same electrolyte. Good capacitance retention of 90 % was obtained while charge-discharging (CD) the device for about 10,000 cycles at 5Ag−1. The CD cycling also yielded a coulombic efficiency of 99.8 %. Thus, this porous carbon produced via cross-linking and heteroatom doping, has a well-connected hierarchical porous structure that includes both micropores and mesopores. This structure is important for charge storage and transport. Therefore, the fabricated symmetric cell is a promising supercapacitor energy storage device, where a high power is requisite.