Supercapacitor nanoporous carbon electrodes

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. 

Synthesis and Characterization of Nanoporous Carbon and Its Electrochemical Application to Electrode Material for Supercapacitors... 

This volume contains four chapters. The topics covered are solid state electrochemistry devices and techniques nanoporous carbon and its electrochemical application to electrode materials for supercapacitors the analysis of variance and covariance in electrochemical science and engineering and the last chapter presents the use of graphs in electrochemical reaction networks. 

In order to satisfy the industrial demand, the performance of supercapacitors must be improved and new solutions should be proposed. The development of new materials and new concepts has enabled important breakthroughs during the last years. In this forecast, carbon plays a central role. Due to its low cost, versatility of nanotextural and structural properties, high electrical conductivity, it is the main electrode component. Nanoporous carbons are the active electrode material, whereas carbon blacks or nanotubes can be used for improving the conductivity of electrodes or as support of other active materials, e.g., oxides or electrically conducting polymers. 

As d is of the order of lnm, the specific capacity is very high, e.g., 0.1 F nr2. Nanoporous carbons are ideal materials for supercapacitor electrodes [8], because of their low cost, good electrical conductivity, and very high specific surface area (between 1000 and 2500 m2 g-1). The values of capacity are generally ranging from 100 to 200 F g 1. 

In this context, nanoporous carbons are extremely interesting materials which can be used either as electrodes of supercapacitors or hydrogen reservoir. They are commercially available at a low cost and under various forms (powder, fibers, foams, fabrics, composites) [3]. They can be obtained with well-developed and controlled porosity [4,5] and with a rich surface functionality [6,7], As far as electrochemistry applications are concerned, very important advantages of carbons are a high electrical conductivity, a good chemical stability in various electrolytic media and the possibility to control wettability by the nature of the surface functionality. When they are not playing the role of active material for the storage process, carbons may be also useful as additive in a composite to improve its physical properties. Particularly carbon nanotubes are able to improve the electrical conductivity and mechanical properties of electrodes [8],... 

Liu, B., Shioyama, H., Jiang, H., Zhang, X., Xu, Q., 2010a. Metal-organic framework (MOF) as a template for syntheses of nanoporous carbons as electrode materials for supercapacitor. Carbon 48,456-463. 

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. 

Chaikittisilp W, Hu M, Wang H, Huang H-S, Fujita T, Wu KC-W, Chen L-C, Yamauchi Y, Ariga K (2012) Nanoporous carbons through direct carbonization of a zeoUtic imidazolate framework for supercapacitor electrodes. Chem Commun 48 7259-7261... 

Janes A, Kurig H, Lust E (2007) Characterisation of activated nanoporous carbon for supercapacitor electrode materials. Carbon N Y 45 1226-1233... 

However, the electrodes which are used in supercapacitors have far more complex topologies than planar surfaces. The nanoporous carbons, such as the nanotubes, " cluster-assembled nanostructured carbons, nano-onions or carbide-derived nanoporous carbons have surfaces which are mostly curved, and can also contain many topological defects. It is important to understand how this impacts the structure of the adsorbed electrolytes and the resulting capacitance of the interface, even in the absence of confinement effects. 

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