Rotating Transparent Disc Electrodes

The traditional technique used to investigate these systems has been flash photolysis. I e have developed a complimentary technique, the rotating transparent disc electrode 13, 14, 15, 16 which is perhaps more appropriate for these investigations. This is because the transparent electrode mimics the illuminated electrode in the cell but with the system, better defined. 

The apparatus is illustrated in figure 4. The transparent disc electrode consists of the end of a quartz rod which is coated with a thin layer of Sn O2 to make the electrode. Light from an ordinary slide projector is focussed on to the top of the rod. The electrode is rotated at speeds between 1 and 50 Hz. This rotation imposes a known pattern of flow on the solution, and this 

In investigating photogalvanic systems we perform two types of experiment. In the first type of experiment we do not add any Fe (III) to the solution. Under these conditions the concentration of photogenerated Fe (III) is so small that the back reaction of L with Fe (III) is negligible. The potential of the electrode is set so that all the photogenerated L which reaches the electrode is destroyed. The photocurrent then varies linearly with W The current 

It can be seen that the use of electrochemical detection allows us to measure directly the efficiency of the forward reaction of the photogalvanic system. 

In the second type of experiment we add Fe (III) to the solution. Now two types of behaviour may be found. First of all, at high rotation speeds the photo- 

---

Fig. 4. The Rotating Transparent Disc Electrode. The dotted arrows show the imposed hydrodynamics. The four insets show how the fate of L depends on W the rotation speed and k 2-...

The ORDE consists of a quartz rod, polished at both ends, one of which is coated with a quasi-metallic antimony-doped tin oxide film to form a (semi-) transparent disc electrode. Light is shone down the rod and through the disc electrode as it is rotated in solution. The rotation of the ORDE imposes RDE hydrodynamics at the transparent... 

According to their size, in particular to their typical dimensions, electrodes are called macroelectrodes with typical dimension (e.g., diameter of a disc-shaped electrode, length of the edge of a sheet electrode) in the range of mm or cm, microelectrodes (with pm), and nanoelectrodes (with nm). Electrodes for particular methods are called rotating disc electrodes (see entry Controlled How Methods for Electrochemical Measurements ), optically transparent electrodes (OTL, see entry UV-Vis Spectroelectrochemistry ), and thin-layer electrodes (TLE for electrolysis with a limited solution volume present as a thin layer of liquid). 

For the investigator who wants to study electrode processes at depth, a number of more physically oriented methods are available, such as double layer capacitance measurements19 rotating disc and ring disc techniques 25 and radio-. active tracer methods 40a Spectroscopical methods in conjunction with optically transparent electrodes can be used for the study of intermediates 40b), as can also total reflectance spectroscopy 40c). 

---