Optimization of the characterization of porous carbons for supercapacitors

Abstract

The optimization of carbon-based supercapacitors is of great technological importance for electrical energy storage. This challenge stresses the relevance of current attempts to increase the surface-related capacitance C/S (F m -2 ) of carbons. We show that for microporous carbons this property is practically constant for pore widths between 0.7 and 1.8 nm. The study is based on two independent approaches, (i) the effective surface area accessible to the ions, which may differ considerably from the BET-surface and (ii) the volumetric capacitance in the micropores. One obtains 0.094 F m -2 for (C 2 H 5 ) 4 NBF 4 /acetonitrile and approximately 0.100 F m -2 in aqueous H 2 SO 4 after correcting for pseudo-capacitance effects. This pattern is supported by recent modelling which takes into account the solvent. It is also suggested that constant values of the surface based-capacitance may reflect a gradual decrease of the dielectric constant of the electrolytes in smaller micropores due to desolvation.

Investigation of the Electrochemical Properties of CoAl-Layered Double Hydroxide/Ni(OH)2

“…Electrochemical capacitors (ECs), also known as supercapacitors, 1,2 are a new type of energy storage device that have been developed in recent years. Typically, according to the charge storage mechanism of different electrode materials, [3][4][5] the use of supercapacitors can be divided into two categories including the electric double layer capacitor (EDLC), Faraday pseudocapacitor and hybrid supercapacitor. [6][7][8][9] The electric double layer capacitor uses high surface area carbon as the electrode material, while the Faraday pseudocapacitor uses a transition metal oxide or a conductive polymer as an electrode material.…”

Graphite Oxide: An Interesting Candidate for Aqueous Supercapacitors

“…Even using the surface estimated by CO 2 , the present carbon exhibits a much higher capacitance per specific surface area (in F m -2 ) than other porous carbons [29,34]. This suggest that the specific surface area determined by standard gas adsorption (i.e.…”

“…This value and the surface capacitance of 0.105 F m -2 [29,34] found for carbons in the aqueous electrolyte allows estimating a pseudocapacitance of 69 Fg -1 which corresponds to ~ 44 % of the overall capacitance of the graphite oxide in 2M H 2 SO 4 .…”

“…Taking into account a contribution from the double layer in the organic electrolyte of around 0.095 F m -2 (obtained by a systematic study of a large variety of carbon materials) [29,34], one obtains that the surface of S43 participating in energy storage would be around 860 m 2 g -1 .…”

Electrochemical Capacitors Based on Carbon Electrodes in Aqueous Electrolytes

“…Because of the fact that in all computational methods there are some assumptions and limitations, Stoeckli et al [53,54] have correlated the capacitance properties of 28 porous carbons of different origins with their average surface area S av determined by combining gas adsorption and immersion calorimetry. Contrary to the anomalous increase of C/S BET (F m −2 ) for TiC-based carbons in pores of less than 1 nm for the TEABF 4 /AN electrolyte [55], the C/S av values remain relatively constant in slit-shaped micropores of 0.7-1.8 nm [54,56,57].…”