Materials spectroelectrochemical

The chaimel-flow electrode has often been employed for analytical or detection purposes as it can easily be inserted in a flow cell, but it has also found use in the investigation of the kinetics of complex electrode reactions. In addition, chaimel-flow cells are immediately compatible with spectroelectrochemical methods, such as UV/VIS and ESR spectroscopy, pennitting detection of intennediates and products of electrolytic reactions. UV-VIS and infrared measurements have, for example, been made possible by constructing the cell from optically transparent materials. 

Most 2,5-unsubstituted pyrroles and thiophenes, and most anilines can be polymerized by electrochemical oxidation. For pyrroles, acetonitrile,54 or aqueous55 electrolyte solutions are normally used, while the polymerization of thiophenes is performed almost exclusively in nonaqueous solvents such as acetonitrile, propylene carbonate, and benzonitrile. 0 Polyanilines are generally prepared from a solution of aniline in aqueous acid.21 Platinum or carbon electrodes have been used in most work, although indium-tin oxide is routinely used for spectroelectrochemical experiments, and many other electrode materials have also been employed.20,21... 

FIGURE 27.3 Spectroelectrochemical cell for in situ XRD on battery electrode materials. 

Fignre 27.3 shows a typical spectroelectrochemical cell for in sitn XRD on battery electrode materials. The interior of the cell has a construction similar to a coin cell. It consists of a thin Al203-coated LiCo02 cathode on an aluminum foil current collector, a lithium foil anode, a microporous polypropylene separator, and a nonaqueous electrolyte (IMLiPFg in a 1 1 ethylene carbonate/dimethylcarbonate solvent). The cell had Mylar windows, an aluminum housing, and was hermetically sealed in a glove box. 

De Souza et al. (1997) used spectroscopic ellipsometry to study the oxidation of nickel in 1 M NaOH. Bare nickel electrodes were prepared by a series of mechanical polishing followed by etching in dilute HCl. The electrode was then transferred to the spectroelectrochemical cell and was cathodicaUy polarized at 1.0 V vs. Hg/HgO for 5 minutes. The electrode potential was then swept to 0.9 V. Ellipsometry data were recorded at several potentials during the first anodic and cathodic sweep. Figure 27.30 shows a voltammogram for Ni in l.OM NaOH. The potentials at which data were recorded are shown. Optical data were obtained for various standard materials, such as NiO, a -Ni(OH)2, p-Ni(OH)2, p-NiOOH, and y-NiOOH. 

Spectroelectrochemical analysis of charge-insertion nanostructured materials already offers important insight into these systems. These methods were recently exploited to characterize the electrochemical processes of nanostructured manganese oxide ambi-gel and xerogel films. " 6-229 Spectroelectrochemical measurements were used to corroborate electronic state changes with the observed electrochemical response for the insertion of small cations (Li+, Mg2+) and the unexpected insertion of a bulky organic cation (tetrabutylammonium). Vanadium pentoxide exhibits two distinct electrochromic features that can be assigned to the transition at either sto-... 

In a typical spectroelectrochemical measurement, an optically transparent electrode (OTE) is used and the UV/vis absorption spectrum (or absorbance) of the substance participating in the reaction is measured. Various types of OTE exist, for example (i) a plate (glass, quartz or plastic) coated either with an optically transparent vapor-deposited metal (Pt or Au) film or with an optically transparent conductive tin oxide film (Fig. 5.26), and (ii) a fine micromesh (40-800 wires/cm) of electrically conductive material (Pt or Au). The electrochemical cell may be either a thin-layer cell with a solution-layer thickness of less than 0.2 mm (Fig. 9.2(a)) or a cell with a solution layer of conventional thickness ( 1 cm, Fig. 9.2(b)). The advantage of the thin-layer cell is that the electrolysis is complete within a short time ( 30 s). On the other hand, the cell with conventional solution thickness has the advantage that mass transport in the solution near the electrode surface can be treated mathematically by the theory of semi-infinite linear diffusion. 

Normal reflection optics have been used to advantage with bulk electrode materials. Examples of this type of spectroelectrochemical cell are shown in Figure 9.11 [67]. Simple bifurcated fiber-optic waveguides are used to direct source light onto reflective bulk electrode surfaces and to collect the reflected light for transmission to a detector. This is a simple means for performing spectroelectrochemical experiments at bulk metal electrodes that cannot be as... 

It should be emphasized that a noble gas environment containing atmospheric contaminants at the ppm level cannot be considered inert for sensitive electrodes such as active metals. The inertness of a glove box atmosphere can be sufficient for preparation and work with nonaqueous solutions at low H20, 02, C02 and N2 contamination levels. Work with active metal electrodes, especially when spectroelectrochemical studies are important, requires special electrode surface preparation, as described later. As a rule, a glove box may be sufficient for maintaining a low contamination level in bulk materials, but not on active surfaces. 

Historically, OTEs were used to investigate complex redox reactions including mediated reactions of enzymes (-> mediators). Recently OTEs have been extensively applied to study spectroelectrochemical properties of thin films of electrochromic materials (- elec-trochromic devices, -> electrochromism), and various chromic deposits including bioelectrochemical materials (e.g. - enzymes) or network films of gold -> nanoparticles. They are often used in -> photoelectrochemistry as electrode materials. 

Spectroelectrochemical experiments in which the potential sequence is applied in both directions in a repetitive fashion allow an assessment of the stability of the electrogenerated species, which was indeed confirmed for both the Fe(III)TMPyP and Co(III)TMPyP systems. Yet another virtue of this methodology is the expedient preparation and spectroscopic characterization of reduced and oxidized forms of materials without the need for synthesizing often highly reactive and thus difficult to handle species. 

A general idea of the anticipated redox range of the system under investigation is usually adequate to determine the ideal optically transparent electrode material however, the success of the spectroelectrochemical experiment may be determined by the pristine condition of the electrode. The working electrode. 

Further, the CC stretching around 2000 cm of oligoacetylene/cumulene redox systems is well suitable for monitoring by IR-SEC. Such organo-metallic or sometimes even Werner-type systems have received attention as basic models of redox-active C materials.An example with ligand system 13 showed the spectroelectrochemically characterised intermediate between a 1,3-diyne (diacetylene) and an 1,2,3-triene (cumulene) form with the respective C-C multiple bond-stretching features. 

Figure 8 shows the transmission cell employed by O Grady and co-workers in the study of the nickel oxide electrode. Heineman and co-workers have employed a cell with reticulated vitreous carbon as an electrode material in x-ray spectroelectrochemical studies of various transition metal complexes. 

For Raman spectroelectrochemical studies of electrode materials with... 

Despite the remarkable success achieved in non-enhanced Raman studies of species at metal surfaces in UHV conditions [23], relatively little attention has been given in recent years to spectroelectrochemical studies of species and reactions at electrodes which do not show enhancement effects. The classical electrode materials Pt and Hg are in this category, although some worthwhile Raman enhancement may be obtained by alloying these metals with Ag or Au. 

The applications of TCO materials are enormous. They can be used for deicing, heating, and, particularly, as electrical contacts in optical devices, such as photo-voltaic cells [5, 6], electrochromics [7] or spectroelectrochemical set-ups [8]. 

Cotton et al. Already in their preliminary work, the authors explored the potentialities and goals of the SERRS technique for possible applications to bioanalytical problems. The first possibility is enhanced sensitivity for the RR scattering of scarce materials. A second possibility can be added specifically to redox-active chromophores in proteins. Indeed, this new spectroelectrochemical method permits the simultaneous study of an electrochemical reaction in a biological system in conjunction with a specific measurement of subtile variations in the vibrational spectrum of the chromophores. Another striking feature of the SERRS spectroscopy is that fluorescence of the adsorbate can be completely quenched by the metal surface which generates a high-quality Raman spectrum Another common application of SERRS spectroscopy is the study of the adsorption behaviour and conformation of biomolecules at the metal/electrolyte interface. 

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