Voltammetry, solid state electrodes

Sodium-silicate glass, 151 Sol-gel films, 120, 173 Solid electrodes, 110 Solid state devices, 160 Solvents, 102 Speciation, 84 Spectroelectrochenristry, 40 Spherical electrode, 6, 8, 9, 61 Square-wave voltammetry, 72, 92 Staircase voltammetry, 74 Standard potential, 3 Standard rate constant, 12, 18 Stripping analysis, 75, 79, 110 Supporting electrolyte, 102 Surface-active agents, 79... 

These drawbacks can be avoided to a large extent, using the voltammetry of microparticles—a technique involving solid state electrochemistry where down to about 10 to 10 mol of sample [74-78] can be transferred by abrasion into the surface of an inert electrode, usually paraffin-impregnated graphite electrodes, and the electrode is later immersed in a suitable electrolyte for recording its voltam-metric response. The response of this sample-modified electrode, consisting of the reduction or oxidation of the solid materials, becomes phase-characteristic. 

In this equation, aua represents the product of the coefficient of electron transfer (a) by the number of electrons (na) involved in the rate-determining step, n the total number of electrons involved in the electrochemical reaction, k the heterogeneous electrochemical rate constant at the zero potential, D the coefficient of diffusion of the electroactive species, and c the concentration of the same in the bulk of the solution. The initial potential is E/ and G represents a numerical constant. This equation predicts a linear variation of the logarithm of the current. In/, on the applied potential, E, which can easily be compared with experimental current-potential curves in linear potential scan and cyclic voltammetries. This type of dependence between current and potential does not apply to electron transfer processes with coupled chemical reactions [186]. In several cases, however, linear In/ vs. E plots can be approached in the rising portion of voltammetric curves for the solid-state electron transfer processes involving species immobilized on the electrode surface [131, 187-191], reductive/oxidative dissolution of metallic deposits [79], and reductive/oxidative dissolution of insulating compounds [147,148]. Thus, linear potential scan voltammograms for surface-confined electroactive species verify [79]... 

If all A, B, and R compounds are electroactive in a suitable electrolyte, voltam-mograms of the mixture must provide peaks corresponding to their respective redox processes. In solid-state voltammetry, in which separate microparticles of each one of the electroactive compounds are mechanically transferred to the surface of an inert electrode, independent electrochemical processes must occur. Accordingly, peak currents, ip j) j =A,B,R), recorded for A-, B-, and R-centered voltammetric processes, can generally be taken as proportional to the amount of each one of the compounds deposited on the electrode [131, 243-245]. If separate peaks are recorded for A, B, and R, the respective peak currents must satisfy the relationship... 

The electrochemical behavior of poly(ferrocenylsilanes) has been studied at three levels—in solution by cyclic voltammetry, as films deposited on electrodes, and in the solid state via iodine doping. Solution cyclic voltammetric oxidation and reduction has shown that the polymer, where R/R is Me/Me, reversibly oxidizes in methylene chloride in two stages, apparently with the first oxidation being on alternating iron atoms along the chain.29 Films cast on electrodes behave in a similar way and also show an electrochromic response to oxidation and reduction.30... 

Electroactivity (electroactive or electrochemically active compounds) — The capability of a substance to take part in a faradaic electrode reaction. Electroactive compounds can be in the gaseous, liquid, or solid state or they may be dissolved in (liquid or solid) solutions. Various compounds are also electroactive in the adsorbed state (see -> adsorption, - adsorptive accumulation, -> adsorptive stripping voltammetry) or as polymer films (see -> polymer-modified electrodes) on electrodes. 

Solid-state electrochemistry — is traditionally seen as that branch of electrochemistry which concerns (a) the -> charge transport processes in -> solid electrolytes, and (b) the electrode processes in - insertion electrodes (see also -> insertion electrochemistry). More recently, also any other electrochemical reactions of solid compounds and materials are considered as part of solid state electrochemistry. Solid-state electrochemical systems are of great importance in many fields of science and technology including -> batteries, - fuel cells, - electrocatalysis, -> photoelectrochemistry, - sensors, and - corrosion. There are many different experimental approaches and types of applicable compounds. In general, solid-state electrochemical studies can be performed on thin solid films (- surface-modified electrodes), microparticles (-> voltammetry of immobilized microparticles), and even with millimeter-size bulk materials immobilized on electrode surfaces or investigated with use of ultramicroelectrodes. The actual measurements can be performed with liquid or solid electrolytes. 

Salgado,L., Tejo, G., Meas, Y., and Zayas, T. 2006. Cyclic voltammetry and electrochemical quartz crystal microbalance studies of a rhodized platinum electrode in sulfuric acid solution. Journal of Solid State Electrochemistry 10, 230-235. 

Many electrochemical conversions of solid compounds and materials, including for example the corrosion of metals and alloys or the electrochemical conversions of most battery materials, take place within a liquid electrolyte environment, with the classic approach to investigation comprising macro-sized electrodes. However, in order to obtain a comprehensive understanding ofthe mechanism ofthese solid-state electrochemical reactions, the simple technique of immobilizing small amounts of a solid compound/material on an inert electrode surface provides an easy, yet sometimes exclusive, access to their study. In this chapter is presented a survey of the recent developments of this approach, which is referred to as the voltammetry of immobilized microparticles (VIM). Attention is also focused on progress in the field of theoretical descriptions of solid-state electrochemical reactions. 

The organic and organometallic complexes of transition metals are especially important in catalysis and photovoltaics, on the basis of their redox and electron-mediating properties. Whilst most complex compounds can be studied in (organic) solution-phase experiments, their solid-state electrochemistry (often in an aqueous electrolyte solution environment) is in general also easily accessible by attaching microcrystalline samples to the surface of electrodes. Quite often, the voltammetric characteristics of a complex in the solid state will differ remarkably from its characteristics monitored in solution. Consequently, chemical, physical or mechanistic data are each accessible via the voltammetry of immobilized microparticles. 

Copper has been measured in soil using a portable electroanalytical device based on stripping voltammetry. In marine chemistry, sediments have been sampled and analysed in real-time by in situ solid-state voltammetric micro-electrodes. The analyser was used to examine levels of various redox species and trace metals, e.g. iron and manganese, in salt marsh sediments and other matrices. 

---