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. 

This contains a good overview of spectroelectrochemical teclmiques. 

Some halogenometalate species have been observed to have formed spontaneously during spectroelectrochemical studies in ionic liquids. For example, [MoCl ] (which is hydrolyzed in water, is coordinated by solvent in polar solvents, and has salts that are insoluble in non-polar solvents) can only be observed in basic (X(A1C13) < 0.5 chloroaluminate ionic liquids [1]. FFowever, this work has been directed at the measurement of electrochemical data, rather than exploitation of the ionic liquids as solvents for synthesis [2]. It has been shown that the tetrachloroa-luminate ion will act as a bidentate ligand in acidic X(A1C13) > 0.5 chloroaluminate ionic liquids, forming [M(AlCl4)3] ions [3]. This was also the result of the spontaneous formation of the complexes, rather than a deliberate attempt to synthesize them. 

FIGURE 2-10 Thin-layer spectroelectrochemical cell. OTE = optically transparent electrode. 

FIGURE 2-11 Spectra for a series of applied potentials (mV vs. Ag/AgCl) during thin-layer spectroelectrochemical experiment on 1.04 x 10 3 M [Tc(III)(dmpe)2Br2]+. Medium is dimethylformamide containing 0.5 M TEAP = tetraethylammonium perchlorate. (Reproduced with permission from reference 27.)... 

Spectroelectrochemical experiments can be used to probe various adsorp-tion/desorption processes. In particular, changes in the absorbance accruing from such processes can be probed utilizing the large ratio of surface area to solution volume of OTEs with long optical path length (29). Additional information on such processes can be obtained from the Raman spectroelectrochemical experiments described later. 

Infrared spectroelectrochemical methods, particularly those based on Fourier transform infrared (FTIR) spectroscopy can provide structural information that UV-visible absorbance techniques do not. FTIR spectroelectrochemistry has thus been fruitful in the characterization of reactions occurring on electrode surfaces. The technique requires very thin cells to overcome solvent absorption problems. 

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... 

Amemiya etal.206 have combined spectroelectrochemical and impedance experiments to probe the origin of high-frequency semicircles in... 

Optically active molecules show circular dichroism. Their extinction coefficients f l and are different and change as a function of wavelength. Using a suitable spectroelectrochemical cell, Af = fl -which is usually small compared to conventional extinction coefficients, can be measured. Combined with the special properties of a thin layer cell kinetic data can be extracted from CD-data [01 Liu]. (Data obtained with this method are labelled CD.)... 

The electrodesposition process of conducting polymers can be monitored by spectroelectrochemical in situ techniques Especially useful are ellipsometric... 

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. 

FIGURE 27.6 (a) Schematic side view of a spectroelectrochemical cell designed for in situ... 

Reflectance measurements involve measurements of the intensity of light reflected from a flat specular surface of an electrode in a spectroelectrochemical cell. The incident light is polarized either parallel (p) or perpendicular s) to the plane of incidence, as shown in Fig. 27.24. A detector monitors the intensity of the reflected beam. The light is monochromatic, but the spectrometers usually can be tuned over large wavelength ranges. There are excellent reviews of reflectance by McIntyre (1973) and Plieth et al. (1992). 

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 Cell Figure 5.4 shows spectroelectrochemical cells used in electrochemical SFG measurements. An Ag/AgCl (saturated NaCl) and a Pt wire were used as a reference electrode and a counter electrode, respectively. The electrolyte solution was deaerated by bubbling high-purity Ar gas (99.999%) for at least 30 min prior to the electrochemical measurements. The electrode potential was controlled with a potentiostat. The electrode potential, current, and SFG signal were recorded by using a personal computer through an AD converter. 

After introduction of the working electrode to the spectroelectrochemical cell, continuous potential cycling was performed to obtain a clean surface before each... 

Figure 12.1 Schematic of the spectroelectrochemistry apparatus at the University of Dlinois. The thin-layer spectroelectrochemical cell (TLE cell) has a 25 p.m thick spacer between the electrode and window to control the electrolyte layer thickness and allow for reproducible refilbng of the gap. The broadband infrared (BBIR) and narrowband visible (NBVIS) pulses used for BB-SFG spectroscopy are generated by a femtosecond laser (see Fig. 12.3). Voltammetric and spectrometric data are acquired simultaneously.

Figures 12.1 and 12.2 show that the spectroelectrochemical cell is basically a thin-layer electrochemistry cell (TLE) with a solution gap of 25 pm [Hubbard, 1973]. The metal working electrode may be polycrystalline or a single crystal. Emptying the gap out of the adsorbate molecules due to molecules oxidation, and refilling via molecular...

Chen YX, Heinen M, Jusys Z, Behm RB. 2006. Kinetics and mechanism of the electrooxidation of formic acid—Spectroelectrochemical studies in a flow cell. Angew Chem Int Ed 45 981-985. 

The photochemical formation and the analysis of the absorption and magnetic circular dichro-ism spectra of the anion radical of zinc phthalocyanine were carried out. A complete assignment of the optical spectrum of the anion radical was proposed.834 Similarly, spectroelectrochemical cells have been used to record absorption and magnetic circular dichroism spectra of zinc phthalocyanines and a band assignment scheme proposed.835... 

Spectroelectrochemical studies at —60°C show a reversible one-electron reduction of the intensely coloured [Tc NX - (X = C1, Br) to [TcvNX4]2-, but the colourless reduced species have not been isolated [18]. 

Gao, G., A. S. Jeevarajan et al. (1996). Cyclic voltammetry and spectroelectrochemical studies of cation radical and dication adsorption behavior for 7,7 -diphenyl-7,7 -diapocarotene. J. Electroanal. Chem. 411 51-56. 

Gao, G., Y. Wurm et al. (1997). Electrochemical quartz crystal microbalance, voltammetry, spectroelectrochemical, and microscopic studies of adsorption behavior for (7E,7 Z)-diphenyl-7,7 -diapocarotene electrochemical oxidation product. J. Phys. Chem. B 101 2038-2045. 

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