Capacitance and surface of carbons in supercapacitors

Abstract

This research is focused in the missing link between the specific surface area of carbons surface and their electrochemical capacitance. Current protocols used for the characterization of carbons applied in supercapacitors electrodes induce inconsistencies in the values of the interfacial capacitance (in F m-2), which is hindering the optimization of supercapacitors. The constraints of both the physisorption of N 2 at 77 K and the standard methods used for the isotherm analysis frequently lead to a misleading picture of the porosity. Moreover, the specific surface area of carbons loses their meaning when the supercapacitor operates with organic electrolytes and ionic liquids and the actual surface involved in charge storage has to be assessed by molecular probes suiting the critical dimensions of the ions. In the case of certain carbons such as graphene type-materials, the voltage-driven mechanism may facilitate the access of electrolyte ions to spaces between carbon layers, providing a larger area than that estimated by gas adsorption. Finally, the morphological and porous features of carbons can be extremely modified when they are processed in electrodes. Due to their impact, all these issues should not be neglected and the characterization protocols must be adapted for this specific application of carbons.

Superior Multifunctional Activity of Nanoporous Carbons with Widely Tunable Porosity: Enhanced Storage Capacities for Carbon‐Dioxide, Hydrogen, Water, and Electric Charge

“…Interestingly, all the adsorptive capacities for EDCL, CO 2 , H 2 and H 2 O vary in a similar manner, linearly with respect to the SSA BET or pore volume (Figures and g). Here it is interesting to note that with respect to the SSA BET the UMCs show relatively high gravimetric as well as areal (surface area normalized capacitance, C SSA ) EDLC capacity when compared to numerous other high surface area carbons in the literature (Figure g–i) . The EDLC capacities (deduced at current loads of 0.5–1.0 A g −1 ) of the high surface area carbons from literature are summarily presented in Figure g (Table and Table S1 in Supporting Information).…”

“…Here it is interesting to note that with respect to the SSA BET the UMCs show relatively high gravimetric as well as areal (surface area normalized capacitance, C SSA ) EDLC capacity when compared to numerous other high surface area carbons in the literature (Figure 3g-i). [7,9,11,13,[15][16][17][18][19][20][21][22][23]26,34,[49][50][51][52][53][54][55][56][57][58][59] The EDLC capacities (deduced at current loads of 0.5-1.0 A g −1 )…”

“…The aqueous EDLC capacities between 300-320 F g −1 at 500 mA g −1 in our PMCs/CMCs with specific porosity characteristics outperform many of the other high surface area carbons (Figures 3g and 4f, and Figures S9 and 10 and Table S1 in Supporting Information). [7,9,11,13,[15][16][17][18][19][20][21][22][23]26,34,[49][50][51][52][53][54][55][56][57][58][59] This clearly indicates that most of the samples with ultrahigh porosity, for example, the samples with SSA BET greater than 2500 m 2 g −1 show reduced tendency in their EDLC values, and associated areal capacities are lower than 10 µF cm −2 (Figure 3h). Our PMCs/CMCs with top gravimetric capacities simultaneously show impressive areal capacities, between 16 and 12 µF cm −2 .…”

Steam and Carbon Dioxide Co-Activated Silicon Carbide-Derived Carbons for High Power Density Electrical Double Layer Capacitors

“…For materials with high proportion of ultramicropores, CO 2 adsorption has to be implemented for better estimation due to the fact that CO 2 can more easily access ultramicropores. 5,6,14 The specific surface area, S BET , and other parameters for the carbon materials were calculated according to Brunauer-Emmett-Teller (BET) theory (Table II). 15,16 The total volume of pores (V tot ) was obtained at the conditions near to saturation pressure p/p 0 = 0.97.…”

“…In electrical-double layer capacitors (EDLC) different carbon materials are used for preparing the hierarchically micromesoporous electrodes. [1][2][3][4][5][6] The use of activated carbon electrodes in EDLC-s is taking advantages of its micro-mesoporous structure to reduce the electrode's electrical resistance and improve energy storage performance. 1 Organic and waste materials are quite often being used to prepare cost-effective carbon materials, but carbide-derived carbons (CDC) have an unique nanoporous structure with a narrow pore size distribution, a possibility to fine-tune the pore size and volume and also they have high electric conductivity.…”