Spectroelectrochemistry in Reflection Mode

In the previous section it was shown that detailed information about electrochemical processes and the kinetics of follow-up chemical reaction steps can be investigated by UV/Vis/NIR spectroelectrochemical experiments in transmission mode in the diffusion layer at optically transparent or microstructured non-transparent electrodes. Many metal electrodes show a high reflectivity and therefore optical spectra may also be recorded under in situ conditions in reflection mode [70, 71]. This approach is essential for the study of adsorbed species, the formation of solid layers at the electrode surface, reactions of solids [72-74], and the redox behaviour of conducting polymer layers [75-77]. Furthermore, in reflection mode, the angle of incidence may be modified and polarised light maybe used in ellipsometry studies [78]. 

By using optical wave-guides for illumination and detection, it is possible to record spectra at a disc electrode during the course of cyclic voltammetric measurements (see Fig. II.6.11). Fixing the disc electrode onto a micrometer screw allows the distance between the electrode and the optical window to be varied in a very much easier way compared with the procedure required in in situ spectroelectrochemical cells working in the transmission mode. In this experimental arrangement, the gap between the electrode surface and the wall with the optical wave-guide defines the diffusion layer thickness and therefore the type of absorbance response or time scale. 

In conclusion, UV/Vis/NIR spectroelectrochemistry in both transmission and reflection mode are extremely useful techniques that yield a wealth of complementary data additional to those obtained in pure electrochemical voltam-metric experiments. Especially when based on computer simulation models, this data may be used to unravel the kinetics and thermodynamics of complex electrode processes. 

for example, Bard AJ, Faulkner LR (2001) Electrochemical methods - fundamentals and applications. 2nd edn. John Wiley, New York 

Dong S, Niu J, Cotton TM (1994) Biochemical spectroscopy. In Abelson JN, Simon MI (eds) Methods in enzymology, vol 246. Academic Press, Orlando, Florida 

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