MODULATED INFRARED-SPECTROSCOPY AT THE ELECTROCHEMICAL INTERFACE

Citation
Jn. Chazalviel et al., MODULATED INFRARED-SPECTROSCOPY AT THE ELECTROCHEMICAL INTERFACE, Applied spectroscopy, 47(9), 1993, pp. 1411-1416
Citations number
20
Categorie Soggetti
Instument & Instrumentation",Spectroscopy
Journal title
ISSN journal
00037028
Volume
47
Issue
9
Year of publication
1993
Pages
1411 - 1416
Database
ISI
SICI code
0003-7028(1993)47:9<1411:MIATEI>2.0.ZU;2-E
Abstract
Performing infrared spectroscopy of chemical species at the electroche mical interface represents a difficult challenge in terms of sensitivi ty (1 monolayer approximately 10(15) species/cm2) and selectivity (pre sence of the electrolyte). These problems are efficiently addressed by using modulation coupled with lock-in detection of the optical signal . The electrode potential, which governs the interface behavior, is th e most straightforward physical quantity that can be modulated. Such a modulation technique may be combined with Fourier transform spectrosc opy by using an interferometer with a very slow scanning speed of the movable mirror (approximately 1-10 mum/s). This approach allows one to reach high sensitivity (typical minimum detectable signal DELTAI/I ap proximately 10(-6) in a single-reflection arrangement). In some specia l cases, other modulations may be of interest, for example, modulation of the light at a semiconducting photoelectrode. A common benefit of these modulation techniques is that the resulting response can be anal yzed as a function of the modulation frequency or by consideration of the phase of the signal at a given frequency. As can be shown for seve ral examples, this analysis allows one to distinguish between the vari ous physical and electrochemical processes taking place at the interfa ce: change of free-carrier concentration beneath the electrode surface or of ion populations in the ionic double layer, adsorption-desorptio n effects, and Faradaic processes, for which useful information on the reaction mechanisms may be obtained.