Spectroelectrochemical cells

Garcia G, SUva-Chong JA, Guillen-Villafuerte O, Rodriguez JL, Gonzalez ER, Pastor E. CO tolerant catal3 ts for PEM fuel cells spectroelectrochemical studies. Catal Today 2006 116 415-21. 

Garcia, G., Silva-Chong, J.A., Guillen-Villafuerte, O. 2006. CO tolerant catalysts for PEM fuel cells spectroelectrochemical studies. Catal. Today 116 415-21. 

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. 

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

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. 

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.)... 

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... 

Figure 26. EXAFS spectroelectrochemical cell (A) front view, (B) top view, (C) side view, (D) assembly (a) auxiliary electrode compartment, (b) working electrode well, (c) reference electrode compartment, (d) X-ray window, (e) inlet port, (f) auxiliary electrode lead, (g) RVC working electrode, (h) Pt syringe needle inlet and electrical contact, (i) Pt wire auxiliary electrode, (j) Ag/AgCl(3M NaCl) reference electrode. (From Ref. 98, with permission.)...

Figure 2.103 A spectroelectrochemical cell based on a coated-glass optically transparent...

Spectroelectrochemical cells for use in the UV-visible region are not, of course, constrained by solvent absorption and can thus be of a reasonable size to give acceptable electrochemical behaviour. However, as with all the in situ techniques discussed in this book, a thin-layer approach is one of the methods employed. 

Figure 2.112 Cyclic voltammograms of a P( electrode immersed in N2-saturated I M NaOH solution, and (a) in the absence and (b) in the presence of I M ethylene glycol. Scan rate 100mVs-1, the voltammograms were taken using the IR spectroelectrochemical cell with the electrode pulled back from the cell window. From Christensen and Hamnett (1989).

This system was subsequently investigated by Christensen et at. (1990) also using in situ FTIR, who observed identical product features (see Figure 3.48). In order first to compare directly the IR spectrum of oxalate generated in situ, the authors took advantage of the surface reactivity of Pt and the poor diffusion of species to and from the thin layer. Thus, a solution of oxalic acid in the electrolyte was placed in the spectroelectrochemical cell, the potential of the platinum working electrode stepped to successively lower values and spectra taken at each step. The spectra were all normalised to the reference spectrum collected at the base potential of 0 V vs. SCE. As a result of the deprotonation of adventitious water ... 

The main goals of this research are (1) to characterize polynuclear rhenium complexes which are capable of multielectron transfer reactions (2) to come up with appropriate conclusions on the redox-initiated transformations of this synthetic analog through the use of a new design of spectroelectrochemical cell and (3) propose possible systems or investigations where infrared spectroelectrochemi-stiy can be very useful. 

Figure 8.5 shows a schematic representation of a cell used for obtaining in situ spectroelectrochemical EPR spectra. This cell has to be constructed from silica or quartz since normal glass or plastic will itself have a paramagnetic signal. The counter electrode (CE) needs to be... 

During in situ UV-vis spectroelectrochemical work, it is easier to obtain spectra by using a single-beam instrument. At the start of the experiment, the analyst sets the absorbance to zero with the in situ cell placed in the path of the beam, so the cell then acts as a spectroscopic blank or ( reference ). Any changes in absorption will relate to the changes in the amounts of each of the redox states within the cell, rather than from the cell itself. 

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. 

In situ eiectrolysis-EPR methods usually employ a wire or grid electrode contained in a conventional flat or tube EPR cell. The constraints on the geometric configuration are such that secondary and reference electrodes are usually remote from the generating electrode, which often leads to problems in the control of the potential nevertheless it is a valuable technique for recording spectra of EPR active intermediates. These and related spectroelectrochemical techniques have been reviewed by Robinson.5... 

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