Nanoporous carbon electrodes

In order to see how the electrode thickness might be optimized in order to provide the lowest electrode resistivity, we have developed a theoretical model to describe the charge/discharge processes in porous carbon electrodes. As a first approximation, let us consider an electrode having two sets of cylindrical pores, namely, nanopores (NP) of less than 3 nm in diameter and transport channels (TC) of more than 20 nm in diameter, with each nanopore having an exit to only one TC. ... 

Lust, E., Nurk, G., Janes, A., Arulepp, M., Permann, L., Nigu, P., and Moller, P. Electrochemical properties of nanoporous carbon electrodes. Condens. Matter Phys. 5, 2002 307-327. 

Figure 3.1. Different types of environments encountered by ions (hexafluorophosfate in green, l-butylS-methylimidazolium in red) and acetonitrile (blue) in nanoporous carbon electrodes (in turquoise) (source Nature Communications). For a color version of the figure, see WWW. iste.co. uk / tarascon / storage.zip...

ASV anodic stripping voltammetry ATP adenosine triphosphate AuE gold electrode CV cyclic voltammetry DPV dififerential pulse voltammetry DPASV differential pulse adsorptive stripping voltammetry GCE assy carbon electrode MFE, mercury film electrode NPGE nanoporous gold electrode SPE screen-printed electrode. 

Reprinted from Journal of Power Sources, 195, Khomenko, V., E. Raymundo-Pinero, and F. Beguin, A new type of high energy asymmetric capacitor with nanoporous carbon electrodes in aqueous electrolyte, 4234-4241, Copyright 2010, with permission from Elsevier.)... 

Besides the modeling and simulations for EDLs in the nanopores, other morphologies of carbon electrodes have also been studied [339,340], Wang et al. [339]... 

FIGURE 2.56 Typical structure of the IL inside electrified pores of the CE)C-1200 material. Blue C-C bonds, red BMI+, and green PFs. (a) Local structure near a positive surface (+0.5 V), the anionic density is enhanced, (b) A single anion in a nanotube-like pore positively polarized (+0.5 V). (c) Same as (a) but near a negative surface (-0.5 V). (Reprinted by permission from Macmillan Publishers Ltd. Nature Materials Merlet, C. et al. 2012. On the molecular origin of supercapacitance in nanoporous carbon electrodes. 11 306-310, copyright 2012.)... 

To enhance the energy density of supercapacitors, it is desirable to use electrodes with very small pores. Experimentally, it has been shown that when pores in carbon electrodes are narrower than 1.0 run, the area-normalized capacitance of these nanopores increases as pore size reduces. This breakthrough was discovered for supercapacitors using organic electrolytes and later for supercapacitors using a RTIL [EMIM] [Tf2N] as electrolyte. 

Merlet C, Rotenberg B, Madden PA, Tabema P-L, Simon P, Gogotsi Y, Salanne M (2012) On the molecular origin of supercapacitance in nanoporous carbon electrodes. Nat Mater 11 306-310... 

Industrial supercapacitors are essentially based on nanoporous carbon electrodes. The reasons of the choice lie in the high availability, low cost, chemical inertness, and good electrical conductivity of activated carbons, as well as a high versatility of texture and surface functionality. For these reasons, this chapter will present the capacitance properties of carbon-based electrodes showing optimization strategies playing on the structure/nanotexture of carbon and the nature of the electrolyte. 

The EDLC is an electric energy storage device based on the dielectric property of the electric double layer at the interface between the electrolyte and a nanoporous carbon electrode such as activated carbon. The charge or discharge process is the adsorption/desorption of the electrolyte ion on the carbon surface as shown in Fig. 3. Conway s book states the details of electrochemical capacitors including the EDLC [3]. 

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