Solid Electrolyte Cyclic Voltammetry

C.G. Vayenas, A. loannides, and S. Bebelis, Solid Electrolyte Cyclic Voltammetry for in situ Investigation of Catalyst Surfaces, J. Catal. 129, 67-87 (1991). 

Because of the geometric change at the working electrode due to growth of the PEVD product, the results from a steady-state potentiostatic study are not applicable to stage I of PEVD. In this study, a solid electrolyte cyclic voltammetry (SECV) method was applied for two reasons ... 

Figure 48 shows the usefulness of solid electrolyte cyclic voltammetry (SECV) for extracting transfer coefficients. The peak potentials are plotted against the logarithm of the sweep rates. The value can be obtained from the slope of the linear regression curve. It is calculated to be 0.63, which is close to the value, 0.59, obtained from the steady-state potentiostatic study. Similarly, based on the equation for anodic peaks. 

Kramer K. E. Rose-Pehrsson, S. L. Hammond, M. H. Tilled, D. Streckert, H. H., Detection and classification of gaseous sulfur compounds by solid electrolyte cyclic voltammetry of cermet sensor array, Analytica Chemica Acta 2007, 584, 78-88. 

Fig. 2 Cyclic voltammograms showing the electrocatalytic reduction of nitrite at PANI/polyoxometalate coated electrodes. Electrolyte 0.2 M Na2S04 + H2SO4 (pH =2). Scan rate = 5 mV s . Solid line cyclic voltammetry, restricted to the stability domain of PANI, of the PANI/SiMoi2 assembly, in the supporting electrolyte Dotted line effect of the addition of 10 M NaN02 to the electrolyte.

J. Yi, A. Kaloyannis, and C.G. Vayenas, High Temperature cyclic voltammetry of Pt electrodes in solid electrolyte cells, Electrochim. Acta 38(17), 2533-2539 (1993). 

They first reported and studied permanent NEMCA and via cyclic voltammetry established the dependence of metal/solid electrolyte capacitance on porous metal film mass, which confirms the O2" backspillover promoting mechanism. 

Figure 16.9 Comparison of cyclic voltammetry in a CO-saturated electrolyte (0.5 M HCIO4) of Au supported on carbon (solid curves) and titania (dashed curves) for four different particle sizes (indicated). The measurements were made at a temperature of 298K and a scan rate of 50mV s ...

The reduction of Ti4+ to Ti3+ in TS-1 has also been observed with cyclic voltammetry using zeolite-modified carbon paste electrodes. With silicalite, neither anodic nor cathodic processes can be observed. However, TS-1 is electrochemically active, with a reduction process at +0.56 V versus a saturated calomel electrode (SCE) and an oxidation process at +0.65 versus SCE. These observations must be attributed to the redox system Ti4+/Ti3 +. The electrochemical process involves the Ti cations of the inner part of the zeolite crystals, provided that a suitable electrolyte cation can diffuse inside the channels to compensate for the electrical imbalance caused by the redox process in the solid ... 

Recently a series of dialkylpyrrolidinium (Pyr+) cations have been studied in our laboratory 7-9). These cations are reduced at relatively positive potentials and could be investigated electrochemically as low concentration reactants in the presence of (C4H9)4N+ electrolytes. Using cyclic voltammetry, polarography and coulometry, it was shown that Pyr+ react by a reversible le transfer. The products are insoluble solids which deposit on the cathode and incorporate Pyr+ and mercury from the cathode. Both the cation and the metal can be regenerated by oxidation. Quantitative analysis of current-time transients, from potential step experiments, showed that the kinetics of the process involve nucleation and growth and resemble metal deposition. 

The technique of cyclic voltammetry or, more precisely, linear potential sweep chronoamperometry, is used routinely in aqueous electrochemistry to study the mechanisms of electrochemical reactions. Currently, cyclic voltammetry has become a very popular technique for initial electrochemical studies of new systems and has proven very useful in obtaining information about fairly complicated electrochemical reactions. There have been some reported applications of cyclic voltammetry for solid electrochemical systems. It is worth pointing out that, although the theory of cyclic voltammetry originally developed by Sevick, ° Randles, Delahay, ° and Srinivasan and Gileadi" and lucidly presented by Bard and Faulkner, is very well established and understood in aqueous electrochemistry, one must be cautious when applying this theory to solid electrolyte systems of the type described here, as some non-trivial refinements may be necessary. 

The necessary porosity for thicker layers was introduced by appropriate current densities [321-323], by co-deposition of composites with carbon black [28, 324] (cf. Fig. 27), by electrodeposition into carbon felt [28], and by fabrication of pellets from chemically synthesized PPy powders with added carbon black [325]. Practical capacities of 90-100 Ah/kg could be achieved in this way even for thicker layers. Self-discharge of PPy was low, as mentioned. However, in lithium cells with solid polymer electrolytes (PEO), high values were reported also [326]. This was attributed to reduction products at the negative electrode to yield a shuttle transport to the positive electrode. The kinetics of the doping/undoping process based on Eq. (59) is normally fast, but complications due to the combined insertion/release of both ions [327-330] or the presence of a large and a small anion [331] may arise. Techniques such as QMB/CV(Quartz Micro Balance/Cyclic Voltammetry) [331] or resistometry [332] have been employed to elucidate the various mechanisms. 

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. 

The promotional index, Pip [Eq. (2)]. After the establishment, via the use of surface spectroscopy (XPS [87,88], UPS [89], TPD [90], PEEM [91], STM [92], work function measurements [93]) but also electrochemistry (cyclic voltammetry [90], potential programmed reduction [94], AC impedance spectroscopy [43,95]), that electrochemical promotion is due to the potential-controlled migration (reverse spillover or backspillover) [13] of promoting ionic species (0 , Na", H, F ) from the solid electrolyte to the gas-exposed catalyst surface, it became clear that electrochemical promotion is functionally very similar to classical promotion and that the promotional index PI, already defined in Eq. (2), can be used interchangeably, both in classical and in electrochemical promotion. 

Likewise, Komorsky-Lovric et al. investigated the behavior of lutetium bisphtha-locyanine with the voltammetry of microparticles [108]. This solid-state reaction (which may be studied with either square-wave or cyclic voltammetry) was shown to proceed via the simultaneous insertion/expulsion of anion ions. The oxidation was found to have quasi-reversible characteristics in electrolyte solutions containing perchlorate, nitrate, and chloride, whereas bromide and thiocyanate... 

Oxygen ion conductors are used in amperometric sensors for a variety of gas species. The selectivity is controlled by selecting electrode materials that catalyze particular reactions hence, multiple electrodes are required for some multicomponent gas mixtures. In such cases, the system is designed so that each electrode removes a particular gas from the gas stream. The particular gas removed by a particular electrode can also be controlled by the voltage at the electrode, just as in cyclic voltammetry, which has also been used in solid-electrolyte based sensors [34]. In addition to providing selectivity, control of the applied voltage can be used to improve the magnitude of the response [35]. 

Surface excesses of electroactive species are often examined by methods sensitive to the faradaic reactions of the adsorbed species. Cyclic voltammetry, chronocoulometry, polarography, and thin layer methods are all useful in this regard. Discussions of their application to this type of problem are provided in Section 14.3. In addition to these electrochemical methods for studying the solid electrode/electrolyte interface, there has been intense activity in the utilization of spectroscopic and microscopic methods (e.g., surface enhanced Raman spectroscopy, infrared spectroscopy, scanning tunneling microscopy) as probes of the electrode surface region these are discussed in Chapters 16 and 17. 

Gasteiger and Mathias assume a thin-film structure of the ionomer of 0.5-2 nm covering the entire solid catalyst surface. Experimental support for this electrode structure comes from double-layer capacitance measurements using cyclic voltammetry and AC impedance techniques. Gasteiger and Mathias observed values that are typical of Pt and carbon interfaces with electrolyte and imply that the entire solid surface was in contact with electrolyte for these electrodes. Under several assumptions regarding structure, diffusion, and reactivity, a minimum permeability was derived for a maximum of 20 mV loss. 

Although one of the more complex electrochemical techniques [1], cyclic voltammetry is very frequently used because it offers a wealth of experimental information and insights into both the kinetic and thermodynamic details of many chemical systems [2], Excellent review articles [3] and textbooks partially [4] or entirely [2, 5] dedicated to the fundamental aspects and apphcations of cyclic voltammetry have appeared. Because of significant advances in the theoretical understanding of the technique today, even complex chemical systems such as electrodes modified with film or particulate deposits may be studied quantitatively by cyclic voltammetry. In early electrochemical work, measurements were usually undertaken under equilibrium conditions (potentiometry) [6] where extremely accurate measurements of thermodynamic properties are possible. However, it was soon realised that the time dependence of signals can provide useful kinetic data [7]. Many early voltammet-ric studies were conducted on solid electrodes made from metals such as gold or platinum. However, the complexity of the chemical processes at the interface between solid metals and aqueous electrolytes inhibited the rapid development of novel transient methods. 

Applications of cyclic voltammetry are extensive and include the analysis of solids [22] as well as solutions, media with and without added supporting electrolyte, emulsions and suspensions [23], frozen solutions [24], polymers [25], membrane and liquid/liquid systems [26], and biological systems such as enzymes [27] or cultures of bacteria [28]. 

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