Electrochemically modulated

The surface actlve/surface inactive difference between p-polarlsed/ s-polarised radiation has enabled an alternative modulation technique, polarisation modulation, to be developed (15,16). In electrochemical applications, it allows surface specificity to be achieved whilst working at fixed potential and without electrochemical modulation of the interface. It can be implemented either on EMIRS or on SNIFTIRS spectrometers and can be very valuable in dealing with electrochemically irreversible systems however, the achievable sensitivity falls well short of that obtained with electrochemical modulation. It should also be noted that its "surface specificity" is not truly surface but extends out into the electrolyte with decreasing specificity to about half a wavelength. 

It is only since 1980 that in situ spectroscopic techniques have been developed to obtain identification of the adsorbed intermediates and hence of reliable reaction mechanisms. These new infrared spectroscopic in situ techniques, such as electrochemically modulated infrared reflectance spectroscopy (EMIRS), which uses a dispersive spectrometer, Fourier transform infrared reflectance spectroscopy, or a subtractively normalized interfacial Fourier transform infrared reflectance spectroscopy (SNIFTIRS), have provided definitive proof for the presence of strongly adsorbed species (mainly adsorbed carbon monoxide) acting as catalytic poisons. " " Even though this chapter is not devoted to the description of in situ infrared techniques, it is useful to briefly note the advantages and limitations of such spectroscopic methods. 

EMIRS electrochemically modulated infrared reflectance spectroscopy... 

In the early work of Bewick and Robinson (1975), a simple monochromator system was used. This is called a dispersive spectrometer. In the experiment the electrode potential was modulated between two potentials, one where the adsorbed species was present and the other where it was absent. Because of the thin electrolyte layer, the modulation frequency is limited to a few hertz. This technique is referred to as electrochemically modulated infrared reflectance spectroscopy (EMIRS). The main problem with this technique is that data acquisition time is long. So it is possible for changes to occur on the electrode surface. 

Kunimatsu, K. and Bewick, A. (1986) Electrochemically modulated infrared spectroscopy of adsorbed water in the inner part of the double layer part 1. Oxygen-hydrogen stretching spectra of water on gold in 1M perchloric acid. fnd. J. Technol., 24, 407-412. 

Beden B, Bewick A, Lamy C. 1983. A study by electrochemically modulated infrared reflectance spectroscopy of the electrosorption of formic acid at a platinum electrode. J Electroanal Chem 148 147-160. 

Electrochemically Modulated Infra-Red Spectroscopy (EMIRS) [23] consists of applying a square-wave potential modulation to the working electrode and analyzing the modulated part of the IR detector response using a dispersive instrument. 

In recent years,3 4 however, there has been renewed interest in the study of the electrode/solution interface due in part to the development of new spectroscopic techniques such as surface-enhanced Raman spectroscopy,5-7 electrochemically modulated infrared reflectance spectroscopy and related techniques,8,9 second-harmonic generation,10-12 and others which give information about the identity and orientation of molecular species in the interfacial... 

The infrared surface spectroscopic analysis was applied only to gas-solid surfaces imtil Bewick et al. succeeded ) to measure an in situ infiored spectra on electrode surfaces in electrochemical systems. They controlled the electrode potential and obtained the difference spectra between the measured and the reference potentials (EMIRS Electrochemically Modulated Infrared Reflectance Spectroscopy). This technique is employed in this theses also and discussed in detail in a later section. 

Since the STAR-CD does not include an electrochemical module at present, the electrochemical calculations on SOFCs are treated using subroutines produced in-house. 

Electrochemically modulated infrared spectroscopy (EMIRS), involving potential modulation. Modulation frequencies from 1-100 Hz are employed and phase-sensitive detection used to calculate AR. 

Electrochemically modulated surface plasmon resonance (EM-SPR) - surface plasmon resonance... 

It was first shown by electrochemically modulated infrared reflectance spectroscopy (EMIRS) that the main poisoning species formed during the chemisorption and oxidation of methanol on a platinum electrode is carbon monoxide CO, either linearly bonded, or bridge bonded to the surface. The coverage degree of the electrode surface by linearly bonded CO can reach 90% on a pure platinum electrode, so that most of the active sites are blocked... 

Scheme 15. Electrochemical modulation of the orientation of DNA helices bound to a gold electrode surface [269].

Electrochemical modulated infrared (ir) spectroscopy has been used to obtain in situ spectra of the radical anion of benzophenone [5], There is a red shift of the vibrational modes of the benzene rings and considerable loosening of the carbonyl bond. Carbonyl compound radical anions are protonated on the oxygen center. The conjugate acids of alkanones and alkanals have pKg values [6] in the range 11-12, while those from conjugated aromatic carbonyl compounds [7] are in the range 8-10. 

P. V. Kamat S. Barazzouk S. Motchandani, Electrochemical Modulation of Fluorophore Emission at a Nanostmctured Gold Film. Angew. Chem. (Int. Ed.) 2002, 43, 2764-2767. 

Anderson, L.J., Richardson, D.J., and Butt, J.N. (2001) Catalytic protein film voltammetry from a respiratory nitrate reductase provides evidence for complex electrochemical modulation of enzyme activity. Biochemistry, 40, 11294-11307. 

Pretty, J.R. Deng, H. Goeringer, D.E. Van Berkle, G.J. Electrochemically Modulated Preconcentration and Matrix Elimination for Organic Analytes Coupled On-Line with Electrospray Mass Spectrometry, Anal. Chem. 72,2066-2074 (2000). 

Fig. 18. Principles of electrochemical modulation of sensor characteristics by amperometric electrode reactions. E enzyme, S substrate P product M mediator.

LPSIRS Linear Potential Sweep Infra-Red Spectroscopy SPAIRS Single Potential Alteration Infra-Red Spectroscopy PDIRS Potential Difference Infrared Spectroscopy EMIRS Electrochemically Modulated Infra-Red Spectroscopy SERS Surface Enhanced Raman Scattering (Surface Enhanced Raman Spectroscopy)... 

The study of the electrosorption and oxidation of formaldehyde follows the patterns presented above. Thus electrochemically modulated IR reflectance spectroscopy (EMIRS) was used to identify the adsorbed species formed at different potentials in the... 

Wang, R., lyoda, T., Tiyk, D. A, Hashitnoto, K., and Fujishima, A. Electrochemical modulation of molecular conversion in an azobenzene-terminated self-assembled monolayer film An in situ UV-visible and infrared study. Langittuir 1997,13, 4644-4651. 

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