Electrodes with excellent capacitance: Influence of micro-mesoporosity in derived bituminous carbon

Abstract

Mexican bituminous carbon (MXBC) was the subject of a study to investigate whether its performance as an electrical capacitor is comparable to that of other carbon sources. Furthermore, we investigated the role of mesopores, micropores, and surface oxygenated functional group (OFG) populations induced by chemical activation processes that favor a higher capacitance. The proposed activation methodology includes different mass ratios (KOH:MXBC) and N2 thermal treatment. This increases the surface area and modulates the pore size, as determined by N2 isotherms, PXRD, SEM, and Raman studies. The chemical environment was elucidated using high-resolution XPS analysis and electrochemical studies, including EIS, CV (in different electrolytes), and charge/discharge cycles. The obtained materials showed values of capacitance (F g−1): 120 (MXCB), 135.87 (1:1), 152.48 (2:1) and 177.78 (3:1), superior to that reported for Vulcan carbon. The best material features are the following: BET surface of 1196 m2 g−1, micropore volume (Vmic) of 0.15 cm3 g−1 and mesopore-macropore volume of 0.57 cm3 g−1, the greatest homogeneity (C-CO) and several oxygenated functional groups (CO, CO, COO) quantified by XPS, along with the lowest resistivity to ionic transport obtained from electrical equivalent circuit model.