Electrical double-layer capacitors porous carbons

Porous carbons are among the most attractive electrode materials for electric double layer capacitors (EDLC), where the charge accumulation occurs mainly by electrostatic attraction forces at the clcctrode/electrolyte interface [1-3]. Advantages of this class of materials include high surface... 

Highly porous carbons can serve as electrodes in -> super (EDL = electric double layer) capacitors. Their very wide electrochemical window allows their use in nonaqueous (relative) high energy-high power density super (EDL) capacitors. 

Guo, Y., Qi, J., Jiang, Y., et al. (2003). Performance of electrical double layer capacitors with porous carbons derived from rice husk. Mater. Chem. Phys., 80, 704-9. 

Porous carbons for electric double-layer capacitors... 

By using porous carbon materials with a veiy high surface area in both positive and negative electrodes, a large amount of electrical charge was found to be stored, and electric double-layer capacitors (EDLCs) were developed [81,82], The fundamental concept of this capacitor is the formation of electric double-layers on the surface of electrodes, as illustrated in Fig. 28. The total amount of electeic charges aligned in double layers on both electrodes increases by the application of potential difference and it is easily understood to depend on the area of this interface, i.e. the surface area of solid electrodes. 

Zheng, C., L. Qi, M. Yoshio, and H. Y. Wang. 2010. Cooperation of micro- and meso-porous carbon electrode materials in electric double-layer capacitors. Journal of Power Sources 195 4406-4409. 

Senthilkumar, S. T., R. K. Selvan, J. S. Melo, and C. Sanjeeviraja. 2013. High performance solid-state electric double layer capacitor from redox mediated gel polymer electrolyte and renewable tamarind fruit shell derived porous carbon. ACS Applied Materials Interfaces 5 10541-10550. 

It is noteworthy that, in all these models, the electrode surface is considered as a plane whereas, practically in an electrical double-layer capacitor (EDLC), it is a porous material - most often carbon - of highly developed SSA, which might be approximately estimated by gas (generally nitrogen) physisorption. Since the gas molecule used to probe the pore volume and the electrolyte ions display different size and interaction with the material surface, it is obvious that the active surface area that takes part in EDL charging is different from the one evaluated by gas adsorption. 

Activated carbon is a porous carbon material with developed nano-sized pores and a high specific surface area (>1,000 m g ). Nowadays, the technical term nanoporous carbon is very often used to mean activated carbon, but the activated carbon should be strictly defined as a porous carbon prepared by an activation process consisting of a gasification reaction to form the developed nano-sized pore stmcture in the carbon matrix. The activated carbons have been widely utilized as industrial materials, for example, an adsorbent, decolorizing agent, deodorant, and catalyst. The details of the preparation method, pore structure, and applications of activated carbons have been described [1]. The most significant electrochemical application of activated carbons is use as an electrode active material for an electric double-layer capacitor (EDLC). This article reviews the use of activated carbons in an EDLC. 

Moriguchi, L, Nakahara, R, Furukawa, H., Yamada, H., and Kudo, T. 2004. Colloidal crystal-templated porous carbon as a high performance electrical double-layer capacitor material. Electrochem. Solid-State Lett.. 7(8), A221-A223. 

These porous carbons, referred to as MgO-templated carbons, have been applied in various areas such as electrodes for electric double-layer capacitors [88], as absorbents for gasoline, and as anodes for lithium ion batteries. The application of these MgO-templated porous carbons has been reviewed elsewhere in Japanese [89]. 

Morishita T, Soneda Y, Tsumura T, Inagaki M (2006) Preparation of porous carbons from thermoplastic precursors and their performance for electric double layer capacitors. Carbon... 

Double-layer properties of porous carbon materials have been widely investigated in relation to the development of the electrochemical capacitors. For detailed information the reader should consult specialized literature. For porous carbons materials, the double-layer capacitance depends on their specific snrface area [82,83], pore stmcture (notably, the pore size distribntion) [84-87], and their crystalline stmctnre and snrface chemistry [83,88,89], Shi [84] measnred the dc capacitance of varions carbons in a KOH electrolyte and noticed that the overall capacitance may reasonably be described as a sum of the capacitance of micro- and mesopores. Assuming that the electrical double layer propagates into micropores accessible for N2 adsorption, the author estimated the differential donble-layer capacitance per unit of micropore surface area as 15 to 20 p,F/cm. Lower values were reported by Vilinskaya... 

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