EMIRS electrochemically modulated

EMIRS electrochemically modulated infrared reflectance spectroscopy... 

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. 

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)... 

EMIRS electrochemically modulated IR spectroscopy HCL hollow cathode lamp... 

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. 

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. 

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 order to employ a lock-in detection technique, as in EMIRS, the modulation frequency of the potential at the electrode would have to be at least an order of magnitude greater than F(v). Thus, the potential modulation would have to be c. 100 kHz too great to allow sufficient relaxation time for most electrochemical processes to respond. Instead, a slow modulation or single-step approach is employed, as follows ... 

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

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... 

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... 

However, after 1980 the development of in situ infrared spectroscopic techniques have allowed the direct identification of adsorbed intermediates. In terms of methanol oxidation on R, electrochemically modulated infrared reflectance spectroscopy (EMIRS) led to the unambiguous identification of adsorbed CO as the poisoning species. Two adsorbed CO species were identified as being responsible for the poisoning phenomena (i) a linearly bonded species (IR absorption band around 2060 cm ) and (ii) a bridge-bonded species (a small band around 1850-1900 cm ). These results were... 

One of the most commonly applied IR techniques developed to overcome these problems is the external reflectance technique. In this method, the shong solvent absorption is minimized by simply pressing a reflective working electrode against the IR transparent window of the electrochemical cell. The sensitivity problem, that is, the enhancement of the signal/noise ratio in the case of external reflectance techniques is solved by various approaches. These are, for instance, electrochemically modulated infrared spectroscopy (EMIRS), in situ FTIR (which use potential modulation), and polarization modulation infrared reflection absorption spectroscopy (PM-IRAS, FTIR) [86,117-123]. 

Electrochemically modulated infrared spectroscopy (EMIRS), polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and attenuated total reflectance (ATR) have also been used. (FTIR-ATR spectra are shown in Chap. 6, Fig. 6.11.)... 

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