Cells for spectroelectrochemistry

Cells for Spectroelectrochemistry. Spectroscopic techniques have been used in conjunction with electrochemistry in a variety of ways, which can be grouped into three areas the direct optical study of the electrode interface, the... 

In a conventional luminescence experiment, the detector and excitation source must be maintained at a 90° angle to one another in order to limit the amount of excitation Ught reaching the detector. To achieve this requirement, a square clear sided cuvette is needed as shown in Figure 14.14a. The use of such a square cuvette as a cell for spectroelectrochemistry is not easily adaptable to the thin layer or semi-diffusion cell arrangements conventionally used in UV-vis spectroscopy. Two approaches have been taken to circumvent this problem. First, a thin layer cell comparable to that used in an OTTLE experiment, where the cell is positioned at a 45° angle relative to the excitation source and detector, can be used as shown in Figure 14.14b. 

Because silver, gold and copper electrodes are easily activated for SERS by roughening by use of reduction-oxidation cycles, SERS has been widely applied in electrochemistry to monitor the adsorption, orientation, and reactions of molecules at those electrodes in-situ. Special cells for SERS spectroelectrochemistry have been manufactured from chemically resistant materials and with a working electrode accessible to the laser radiation. The versatility of such a cell has been demonstrated in electrochemical reactions of corrosive, moisture-sensitive materials such as oxyhalide electrolytes [4.299]. 

Figure 9.10 Assembly of sandwich-type optically transparent electrochemical cell for extended x-ray absorbance fine structure (EXAFS) spectroelectrochemistry. Cell body is of MACOR working electrode is reticulated vitreous carbon (RVC). [From Ref. 64, with permission.]...

Figure 17.9 Gas-tight transmission cell for UV-visible spectroelectrochemistry in moderate-melting salts. [From G. Mamantov, V. E. Norvell, and L. Klatt, J. Electrochem. Soc. 727 1768 (1980), with permission.)...

Figure 6.22 Cell system for spectroelectrochemistry by use of optically transparent electrodes (OTEs).

Figure 3.18 Illustration of a typical cell used for spectroelectrochemistry experiments in this arrangement, the light beam passes along the vertical axis...

Figure 3-19 Resonance Raman spectroelectrochemistry cells and back scattering geometry. (A) Controlled potentional electrolysis cell (B) sandwich cell for semi-infinite diffusion conditions. (Reproduced with permission from Ref. 73. Copyright 1975 American Chemical Society.)...

Spectroelectrochemistry has become a valued technique coupling spectroscopy and electrochemistry. Spectroelectrochemistry is a bulk electrochemical technique and as such many of the cell requirements discussed above that pertain to BE apply for spectroelectrochemistry. Often concentrations for spectroelectrochemistry are much lower than most electrochemical techniques due to the spectroscopic absorbance requirements. The bulk solution must still be oxi-dized/reduced in spectroelectrochemistry. Large surface area working and auxiliary electrodes are employed as in the bulk methods described above. Cells designed with optically transparent electrodes like thin films of Sn02 or In203 or optically transparent mesh electrodes are employed, otherwise the electrode must be manually removed to record spectra. Optically transparent electrodes can be constructed such that the solution volume to electrode surface area ratio is very small making the BE occm rapidly. 

Figure 7.1 Schematic representation of the in-situ, variable-temperature flat cell for EPR spectroelectrochemistry.

Figure 17.1.2 A Cell for transmission spectroelectrochemistry involving semi-infinite linear diffusion. Light beam passes along vertical axis. [Reprinted from N. Winograd and T. Kuwana, Electroanal. Chem., 7, 1 (1974), by courtesy of Marcel Dekker, Inc.] B Optically transparent thin-layer system front and side views, (a) Point of suction application in changing solutions (b) Teflon tape spacers (c) 1 X 3 in. microscope slides (d) test solution (e) gold minigrid, 1 cm high ...

Fig. 5.6. Spectroelectrochemical cell for in situ UV-Vis spectroelectrochemistry with optically transparent electrodes [39]...

A combination of transmission and external reflectance spectroscopy resulting in a cell for bidimensional UV-Vis spectroelectrochemistry has been described [61]. With an optically transparent electrode (OTL), the schematic setup shown in Fig. 5.8 illustrates the different pathways of the light. One beam passes through the electrode and the electrolyte solution in front of it and the second beam passes only through the solution in front of the electrode close to it, guided strictly in parallel to the surface. Thus the former beam carries information pertaining to both the solution and the electrochemical interface (e.g. polymer films or other modifications on the electrode surface), whereas the latter beam carries only information about the solution phase. Proper data treatment enables separation of both parts. Identification of... 

Fig. 5.38. Thin layer cell for NIR spectroelectrochemistry in the transmission mode according to [142, 144]...

FIGURE A4 Electrochemical cell used for spectroelectrochemistry. An optically transparent electrode such as ITO is shown inside the cuvette. 

Figure 3. First cell for transmission spectroelectrochemistry. (Reproduced with permission from Ref. 12. Copyright 1968 Elsevier).

Figure 2.12 (A) Cell for transmission spectroelectrochemistry involving semi-infinite linear dif-...

Raman spectroelectrochemistry has been reviewed in detail (65, 66). The type of cell used for spectroelectrochemistry depends to some extent on the optical layout of the Raman experiment. The main optical layouts in conventional Raman spectroscopy are front incident and collection mode, 180° backscattering, and ATR mode. For most solution phase applications of Raman spectroeleclrochemistry, a three-electrode cell for bulk electrolysis is used and a number of such cells have been described (67). The conventional OTTLE cell described for electronic spectroscopy can be used in Raman spectroelectrochemistry. However, this cell can suffer from solvent interference in non-aqueous media Thin layer cells like those desaibed for IR are also frequendy used (66). 

Figure 14.27 Spectroelectrochemical cell for Raman, (a) Simple thin layer set-up for Raman spectroelectrochemistry for use with solid films or monolayers and suitable for use with backscattering...

Provisions are also made in the cell for solution sparging (usually with ultrapure Ni gas). This is because the presence of dissolved air (or O2) causes interference with voltammetric measurements. Thin-layer cells are designed to maximize the electrolysis efficiency and are especially suited for spectroelectrochemistry experiments. These are considered later. 

Figure 3 Sandwich cell for transmission measurement under semi-infinite linear diffusion conditions. Reprinted by courtesy of Marcel-Dekker, Inc. from Kuwana T and Winograd N (1974) Spectroelectrochemistry at optically transparent electrodes. I. Electrodes under semi-infinite diffusion conditions. In Bard AJ (ed) Electroanalytical Chemistry. A Series of Advances, Vol 7, pp 1-78. New York Marcel-Dekker.

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.

Figure 8.2 Schematic representation of a cell used for in situ spectroelectrochemistry. Notice how the counter electrode (CE) has two prongs, one either side of the optically transparent working electrode (WE). Neither the reference electrode (RE), nor the CE can be allowed to interrupt the path of the light beam (as indicated by the circle on the front view).

Figure 8.5 Schematic representation of a typical EPR cell - in this case, the Compton-Waller flow cell - used for in situ spectroelectrochemistry. The working electrode is placed outside of the cavity of the EPR spectrometer, with the counter elecUode being normally an SCE or AgCl,Ag . The working electrode is a flat polished plate of platinum, positioned parallel to the direction of the electric field. Reproduced from Compton, R. G. and Waller, A. M., Comprehensive Chemical Kinetics, Vol. 29, p. 173, Copyright (1989), with permission from Elsevier Science.

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