Optically transparent cells

Fig. 11. Dependence of log(itf,h) for single potential step chronoabsorptometric measurements (O) and log(fcb.h) for asymmetric double potential step chronoabsorptometric measurements ( ) on overpotential for Cyt c system at a tin oxide optically transparent cell. CoefB-cients of correlation are as follows data, r = 0.9976 tb,h 0.9846." ...

Optically transparent electrodes (OTEs) can be used to construct optically transparent cells for use in a conventional UV/VIS or IR spectrometer (Plieth et al. 1998). OTEs are of various types, depending on the application, and can include the following ... 

Transmittance spectroscopy and optically transparent cell materials... 

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. 

Method Abs, chemical reduction, monitored by absorption spectroscopy CD, chemical reduction, monitored by CD spectroscopy CD/OTTLE, electrochemical reduction using an optically transparent thin layer (OTTLE) cell, monitored by CD spectroscopy CV, cyclic voltammetry EPR, chemical reduction, monitored by EPR. 

Fig. 5.58 Scheme of a photogalvanic cell. The homogeneous photoredox process takes place in the vicinity of the optically transparent anode (a) or cathode (b)... 

A regenerative photogalvanic cell with oxidative quenching (Fig. 5.58b) is based, for example, on the Fe3+-Ru(bpy)2+ system. In contrast to the iron-thionine cell, the homogeneous photoredox process takes place near the (optically transparent) cathode. The photoexcited Ru(bpy)2+ ion reduces Fe3+ and the formed Ru(bpy)3+ and Fe2+ are converted at the opposite electrodes to the initial state. 

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

The other popular approach to in situ spectroelectrochemistry is based on the use of an OTE electrode in a thin-layer, optically transparent thin layer electrode (OTTLE), cell. A schematic representation of one design of OTTLE cell is shown in Figure 2.105. 

Figure 2.105 Optically transparent thin layer electrochemical (OTTLE) cell. A = PTFE cell body, B = 13 x 2 mm window, (C and E) = PTFE spacers, D = gold minigrid electrode, F = 25 mm window, G = pressure plate, H = gold working electrode contact, 1 = reference electrode compartment, J = silver wire, K = auxiliary electrode and L = solution presaturator. From Ranjith...

Figure 5.10 Redox titration of the Ni-C EPR signal in D. gigas hydrogenase, in the presence of mediators under partial pressure of H2. (A) Titration monitored by EPR spectroscopy (data from Cammack et al. 1982, 1987).The data points were obtained by removing samples from a vessel as shown in Fig. 5.8. Data NiA signal A NiC signal. (B) Titration monitored by FTIR spectroscopy (data from De Lacey et al. 1997).The spectra were recorded directly in a sealed optically transparent thin-layer electrode cell. Note that the oxidized and reduced species, which are undetectable by EPR, can be measured. Data o I946cm (NiB state) 1914+ 1934cm (NiSR state) A 1952cm (NiA state) 1940cm (NiR state).

To learn that in situ spectroeiectrochemistry requires optically transparent electrodes, be aware of the usual materials for making them, and how and why an in situ cell is constructed. 

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).

Fig. 6. UV-visible spectra of 0.05 mM oxidized and reduced recombinant Rhodnius NP3 (a) at pH 7.5 without ligand (b) at pH 7.5 bound to NO (c) at pH 5.5 bound to NO. In each case, the spectrum of the oxidized nitrophorin is represented by a solid line and the reduced by a dashed line. Spectra were recorded in an optically transparent thin-layer electrochemical cell of approximate window thickness 0.05 mm. To obtain the fully oxidized and reduced spectra, potentials (vs Ag/AgCl) were applied until no change in optical spectrum occurred, of -1-600 and —400 mV, respectively (a), -1-200 and —400 mV, respectively (b), and 0 and -280mV, respectively (c).

A high optical transparency is a basic requirement for optical applications. However, conventional polyimides such as PMDA/ODA have a low optical transparency owing to their dark yellow coloration (they are semitransparent, not opaque). Colorless polyimides have been developed for use in space components, such as solar cells and thermal control systems for the first time. ... 

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. 

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