Carbon Electrodes in Electrochemical Technology

Electrochemical technology has a history dating back deep into the nineteenth century and carbon electrodes have been major players in this success [1-4]. In the early cells for both the two largest electrolytic industries, chlor-alkali and aluminum extraction, the electrodes were blocks of carbon or graphite. The past 50 years, however, has seen the development of carbons with different structures and often their availability in a range of forms. Thus, it is possible to purchase electrodes based on graphites, carbons, thermally treated carbons (e.g., vitreous or glassy carbon), expanded carbons, carbon/polymer composites, and doped diamond materials. Moreover, some of these materials are available in many forms as follows  

Edited by Richard C. Alkire, Philip N. Bartlett and Jacek LipkowskL 

This chapter will focus on the carbon materials used in the manufacture of chemicals, flow batteries, and effluent/water treatment. Applications in fuel cells will be dealt with in other chapters. The applications of carbon electrodes have been reviewed previously [2, 3]. 

Some comment about the carbon structures to be met in this chapter is essential. Unlike most chapters in this textbook where the carbons employed are well defined and often fully characterized, the carbon electrodes employed in electrochemical technology are seldom fully characterized and commonly only identified by a manufacturer s/supplier s code [5]. Even when a series of materials are compared, the differences, in terms of structure, are usually poorly specified. 

Materials labeled as carbon are the least defined. There is a material known as amorphous carbon where the carbon atoms are randomly arranged in a three-dimensional array. In reality, however, these materials are probably more likely 

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The aim of this chapter is to call the attention of the reader to a few technology-related issues which are implicit to any kind of complete electrochemical cells. In the following, the case of the carbon electrode in a complete lithium-ion cell will be emphasized. Note that under a cell a single cell is understood a battery is strictly speaking an assembly of two or more cells. 

An electrochemical reaction is a heterogeneous chemical process involving the transfer of charge to or from an electrode, generally a metal, carbon or a semiconductor. The charge transfer may be a cathodic process in which an otherwise stable species is reduced by the transfer of electrons from an electrode. Examples of such reactions which are important in electrochemical technology include ... 

Electronically conducting polymers (ECPs) such as polyaniline (PANI), polypyrrole (PPy) and po 1 y(3.4-cthy 1 cncdi oxyth iophcnc) (PEDOT) have been applied in supercapacitors, due to their excellent electrochemical properties and lower cost than other ECPs. We demonstrated that multi-walled carbon nanotubes (CNTs) prepared by catalytic decomposition of acetylene in a solid solution are very effective conductivity additives in composite materials based on ECPs. In this paper, we show that a successful application of ECPs in supercapacitor technologies could be possible only in an asymmetric configuration, i.e. with electrodes of different nature. 

Electrodes doped with mediators are also successful in analyses using NAD (P)-dependent dehydrogenases (86-88). In these cases, the mediator is firmly adsorbed to the electrode. The cofactor is oxidized by the mediator, which becomes reduced. The mediator is reoxidized by an electrochemical process on the electrode. This technology makes it possible to reduce the amount of cofactor needed, for example, in flow injection analysis and also eliminates the need for enzymatic regeneration systems. A further successful development uses a carbon paste chemically modified with a dehydrogenase, the coenzyme, and a phenoxazine mediator. This complex structure is then coated with a polyester sulfonic acid cation exchanger (86). The mediators used are of aromatic polycyclic structure and are firmly bound to graphite or other carbon electrodes (Fig. 2) (89). 

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