Activated carbon electrochemical behavior

The lure of new physical phenomena and new patterns of chemical reactivity has driven a tremendous surge in the study of nanoscale materials. This activity spans many areas of chemistry. In the specific field of electrochemistry, much of the activity has focused on several areas (a) electrocatalysis with nanoparticles (NPs) of metals supported on various substrates, for example, fuel-cell catalysts comprising Pt or Ag NPs supported on carbon [1,2], (b) the fundamental electrochemical behavior of NPs of noble metals, for example, quantized double-layer charging of thiol-capped Au NPs [3-5], (c) the electrochemical and photoelectrochemical behavior of semiconductor NPs [4, 6-8], and (d) biosensor applications of nanoparticles [9, 10]. These topics have received much attention, and relatively recent reviews of these areas are cited. Considerably less has been reported on the fundamental electrochemical behavior of electroactive NPs that do not fall within these categories. In particular, work is only beginning in the area of the electrochemistry of discrete, electroactive NPs. That is the topic of this review, which discusses the synthesis, interfacial immobilization and electrochemical behavior of electroactive NPs. The review is not intended to be an exhaustive treatment of the area, but rather to give a flavor of the types of systems that have been examined and the types of phenomena that can influence the electrochemical behavior of electroactive NPs. 

Electrochemical behavior of indole-3-propionamide derivatives (Fig. 27) was investigated in order to establish experimental conditions for the electrochemical oxidation and determination of these derivatives using a glassy carbon electrode [158]. Cyclic voltammetry has been used in studying the redox mechanism that is related to antioxidant activity of the derivatives. The results showed that the compounds might have profound effects on the understanding of their in vivo redox processes and pharmaceutical activity. Indole-... 

A major part of the work with nonaqueous electrolyte solutions in modern electrochemistry relates to the field of batteries. Many important kinds of novel, high energy density batteries are based on highly reactive anodes, especially lithium, Li alloys, and lithiated carbons, in polar aprotic electrolyte systems. In fact, a great part of the literature related to nonaqueous electrolyte solutions which has appeared during the past two decades is connected to lithium batteries. These facts justify the dedication of a separate chapter in this book to the electrochemical behavior of active metal electrodes. 

We will mention now two very recently published examples of STM on activated carbons. In one of them, Shi and Shiu [32] studied glassy carbon electrodes before and after electrochemical activation. They reported the development of pores following activation and a change in the electrochemical behavior of the sample, which was related to these structural changes. In the second example, Pfeifer et al. [33] examined a series of activated carbons which displayed an extended fractal network of channels. As expected from such structure, only sparse entrances ( 1.3 nm wide) were observed by STM on the surface of the samples. 

II. PROPERTIES OF ACTIVE CARBONS IMPORTANT FOR THEIR ELECTROCHEMICAL BEHAVIOR... 

Active carbon materials can be used for preconcentration (by adsorption) of diluted electroactive species (e.g.. metal ions). Characterizing the electrochemical behavior of these. systems is therefore important both for electroanalytical [248] and catalytic purposes [242-247,249]. On the other hand, how the adsorbed electroactive species interacts with the electrode material depends on its surface... 

Figure 36 shows the results of CV studies of modified D43/1 active carbon -samples. CVs were recorded in 0.01 M Fe(NOj) solution for carbon samples with (c-c") and without (curves b-b") preadsorbed iron ions. In addition, CVs for carbon samples with preadsorbed iron were recorded in 0.01 M HNOi (curves a-a"). Comparing the electrochemical behavior of the oxidized samples (CWZ—Ox and D—Ox) shows the CVs obtained to be similar. The CV curves... 

The various forms of adsorbed copper can alter the electrochemical behavior of modified carbon samples used as electrode materials (powdered working electrodes in cyclic voltammetry). Figures 45 and 46 show cyclic voltammograms (CVs) for powdered electrodes prepared from selected active carbon samples with and without preadsorbed copper recorded in solution, which do or do not contain Cu " ions. An aqueous solution of 0.5 M NaiS04 as background electrolyte was employed. The CV curves recorded in the solution containing copper ions exhibit a pair of cathodic and anodic peaks, the potentials of which are dependent on the carbon modification procedure and the electrolyte s pH. The estimated peak potentials and the midpoint potentials [formal potentials, Ef = ( p, — p,c)/2] are given in Table 13. 

The electrochemical behavior of the powdered active carbon electrode depends on the surface chemistry, and cyclic voltammetry can be used as a simple method of characterizing active carbon materials. A new heterogeneous copper catalyst was developed using highly porous active carbon as the catalyst support [282]. The advantages of a porous-medium supported catalyst are that the active phase could be kept in a dispersed but stable state, and that, as an example, the oxidized organic pollutant is adsorbed onto carbon, thereby enhancing its surface concen-... 

The role of metal-support interaction on the catalytic activity of carbon-supported Pt nanoparticles toward oxygen reduction and methanol oxidation was analyzed. It was observed that both dispersion and specific activity are influenced by the interaction of the active phase with the support, determining well-defined relationships that may be used for interpreting the electrochemical behavior of new, more advanced catalytic systems. 

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