Interface active carbon-electrolyte solution

Biniak, S., Swiatkowski, A., and Pakula, M. Electrochemical studies of phenomena at active carbon-electrolyte solution interfaces, in Radovic, L. R. (ed.), Chemistry and Physics of Carbon, Vol 27, 2001, New York Marcel Dekker, pp. 125-225. 

Electrochemical Studies of Phenomena at Active Carbon-Electrolyte Solution Interfaces... 

Carbon Materials in Environmental Applications, F. Derbyshire, M. Jagtoyen, R. Andrews, A. Rao, /. Martin-Gullon, andE. A. Grulke IH NMR Spectroscopy of Adsorbed Molecules and Eree Surface Energy of Carbon Adsorbents, V. V. Turov and Roman Leboda Electrochanical Studies of Phenomena at Active Carbon-Electrolyte Solution Interfaces, S. Biniak, A. Swiqtkowski, and M. Pakula Carbon Materials as Adsorbents in Aqueous Solutions, L. R. Radovic,... 

Increase of the electronic state density in the carbon pore walls with the voltage. Hahn et al. [52] have measured double-layer capacitance and electronic conductance of an activated carbon electrode in an aprotic electrolyte solution, 1 mol/dm3 (C2H5)4NBF4 in acetonitrile. Both quantities show a similar dependency on the electrode potential with distinct minima near the potential of zero charge. This correlation suggests that the capacitance, like the conductance, is governed substantially by the electronic properties of the solid, rather than by the ionic properties of the solution in the interface of the double layer. 

In this chapter, attention is given to the cyclovoltammetric studies of phenomena at the interface between chemically and electrochemically modified active carbon and an aqueous or nonaqueous electrolyte solution. Interactions between selected heavy metal ions and an active carbon surface are also discussed. Before the various structural and CV measurement results are considered, a review, together with some pertinent details, will be given in every. section. 

When the electrode is completely immersed in the electrolyte solution, only a two-phase interface (i.e., liquid-solid) is present in the electrode structure. In form it may be either a consolidated powdered active carbon or a confined but unconsolidated bed of carbon particles. These are u.sed for flow-through porous electrodes in many electrochemical systems. The other mode of operation is the gas-diffusion electrode, in which the electrode pores contain both the electrolyte solution and a gaseous phase. Numerous publications [29-31] have reported on a theoretical analysis of flow-through porous electrodes and gas-diffusion electrodes, which takes into account the physicochemical characteristics of carbon electrode materials. There does not seem to be a uniform explanation for the effects of structural and chemical heterogeneity in carbons. 

Therefore the electrochemical response with porous electrodes prepared from powdered active carbons is much increased over that obtained when solid electrodes are used. Cyclic voltammetry used with PACE is a sensitive tool for investigating surface chemistry and solid-electrolyte solution interface phenomena. The large electrochemically active surface area enhances double layer charging currents, which tend to obscure faradic current features. For small sweep rates the CV results confirmed the presence of electroactive oxygen functional groups on the active carbon surface. With peak potentials linearly dependent on the pH of aqueous electrolyte solutions and the Nernst slope close to the theoretical value, it seems that equal numbers of electrons and protons are transferred. 

Kavan [28] and Kijima et al. [29] have used the electrochemical method to synthesize carbyne. This technique may be realized by classical electrochemistry whereby the charge transfer reaction occurs at interface of a metal electrode and liquid electrolyte solution. Electrons in reaction were supplied either through redox active molecules or through an electrode, which contacts an ionically conducting solid or liquid phase and the precursor. In general, the structure and properties of electrochemical carbon may differ considerably from those of usual pyrolytic carbons. The advantage of this technique is the synthesis of carbyne at low (room) temperature. It was shown that the best product was prepared by cathodic defluorination of poly(tetrafluoroethylene) and some other perhalo-//-alkanes. The carbyne... 

Muller, G., Radke, C.J., and Prausnitz, J.M. (1985). Adsorption of weak electrolytes from dilute aqueous solution onto activated carbon. Part I. Single-solute systems. J. Colloid Interface Sci., 103, 466—83. 

Figure 4.1 Schematic of the atomic structure of the active three-phase interface between the metal particle that catalyzes the reaction, the carbon support necessary to conduct electrons, and the polymer electrolyte and solution necessary to conduct protons for electrocatalytic systems.

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