Functional Groups and Pore Size Distribution Do Matter to Hierarchically Porous Carbons as High-Rate-Performance Supercapacitors

Abstract

A series of nitrogen and oxygen enriched porous carbons are prepared from poly- N -phenylethanolamine (PNPEA) and polyaniline (PANI) conducting polymers through pyrolysis, chemical activation, and oxidation processes. Ar or N 2 -adsorption, Fourier transform infrared, and X-ray photoelectron spectroscopy are used to characterize the surface areas, pore volumes, surface chemical compositions, and oxygen and nitrogen content. Mikhail and Brunauer micropore analytical method (MP method) is successfully used to analyze the micropore size distribution of the samples. The electrochemical behavior of the samples is studied in two- and three-electrode cells. The contribution of pseudocapacitance is confirmed by cyclic voltammetry and galvanostatic tests performed in acidic (H 2 SO 4 ) and basic (KOH) media. The potential drop and the equivalent series resistance value certify that the samples with wide micropore size distribution possess low interface resistances. A sample with a Brunauer–Emmett–Teller (BET) surface area of 760 m 2 g –1, nitrogen content of 3.02 at. %, oxygen content of 16.65 at. %, and a wide micropore size distribution presents the best performance, reaching a value of 370 F g –1 at 0.5 A g –1 and 248 F g –1 at 30 A g –1, and maintaining capacitance retention ration of 96% at 1 A g –1 (over 1000 cycles) and 92% at 30 A g –1 (over 10 000 cycles), respectively. The results obtained for all the samples agree with correlation among capacitance, functional group, and porosity, which indicates that an appropriate selection of the surface chemistry, a reasonable pore size distribution, and a moderate BET surface area may be promising to achieve high-rate-performance supercapacitors.