Platinum SNIFTIRS

Iwasita T., Rasch B., Cattaneo E., Vielstich W. 1989. A SNIFTIRS study of ethanol oxidation on platinum. Electrochim Acta 34 1073-1079. 

Figure 1. SNIFTIRS difference spectra of the b3u ring bending node of p-difluorobenzene at a platinum electrode as a function of modulation potential.

On Pt-Sn, assuming that ethanol adsorbs only on platinum sites, the first step can be the same as for platinum alone. However, as was shown by SNIFTIRS experiments [37], the dissociative adsorption of ethanol on a PtSn catalyst to form adsorbed CO species takes place at lower potentials than on a Pt catalyst, between 0.1 and 0.3 V vs RHE, whereas on a Pt catalyst the dissociative adsorption of ethanol takes place at potentials between 0.3 and 0.4 V vs RHE. Hence it can be stated that the same reactions occur at lower potentials and with relatively rapid kinetics. Once intermediate species such as Pt-(COCH3)adsand Pt-(CO)ads are formed, they can be oxidized at potentials close to 0.3 V vs RHE, as confirmed by CO stripping experiments, because OH species are formed on tin at lower potentials [39, 40] ... 

Fig. 18.4. SNIFTIRS spectrum observed between 0.05 V and 0.45 V on a polycrystalline platinum electrode in 0.01 M MeOH/0.5 M H2S04. [From K. Kunimatsu Ber. Buns. Phys.

These pioneering results on smooth platinum obtained by EMIRS were confirmed by the new IR Reflectance Spectroscopy developed by Pons et al. (SNIFTIRS) and Weaver et al. (SPAIRS), able to observe intermediate species produced on carbon (e.g. Vulcan XC-72) supported Pt-based nanoparticles. 

In fact, these procedures (EMIRS or SNIFTIRS) should be used only when the system under study undergo reversible changes with potential [16]. Bipolar bands are obtained in the difference spectrum for species irreversibly adsorbed, if the band-center frequency is shifted with the potential, e.g., CO adsorbed on platinum (Fig. 8 a). But the situation is problematic when the frequency shift with potential is negligible. Then signals cancel out in the computed spectrum. This question has giv-... 

Figure 6 SNIFTIR spectra of CO adsorbed on electrodes of nanometer-scale thin film of platinum supported on different substrate materials, 0.1 M H2SO4, = — 0.20 V, iis = 0.10 V. 

Fig. 42. SNIFTIRS difference spectra from a platinum electrode in 1M NaF and 0.01 M KSCN. Measured at the voltages shown against a fixed base potential of +400mV vs. SCE reference (300 scans at each potential).

Fig. 46. (a) Transmission spectrum of anthracene, KBr pellet, (b) SNIFTIRS difference spectrum for anthracene reduction to the anion radical. Platinum electrode in 0.1 M TBAF in acetonitrile. Modulation potential —1.50 to —2.50 V vs. Ag/Ag+ reference. 

Many studies on carbon monoxide adsorbed on polycrystalline and single crystal Pt, Pd, and Rh electrodes have been carried out during recent years by means of electrochemical methods and IR spectroscopy (EMIRS, SNIFTIRS, IRRAS, etc.), potential-modulated reflectance spectroscopy and other methods.Electrochemical results show that the number of Pt adsorption sites per CO molecule is changing from 2 to 1 with increasing coverage in acidic solution. There is, however, a discussion in the literature about the evaluation of absolute saturation coverage on ordered low-index platinum (and rhodium) electrodes with particular reference to Pt(l 1... 

Zelenay, P. (1992) In situ SNIFTIRS and radiotracer study of adsorption on platinum trifluoromethane sulfonic acid and phosphoric acid. Electrochem. Transit., 81, 9. 

T. Iwasita, B. Rasch, E. Cattaneo, W. Vielstich, A sniftirs study of ethanol oxidation on platinum, Electrochim. Acta 34 (1989) 1073-1079. 

FIGURE 45. IR spectra of tetracyanoethylene (TCNE) (a) Transmission spectrum of TCNE (b) SNIFTIRS spectrum recorded during the reduction of TCNE in acetonitrile at a platinum electrode (potential pulses between +0.25 V and -0.25 V versus the 0.01 M Ag /Ag reference electrode). 

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