In situ IR reflectance spectroscopy

Vigier F, Coutanceau C, Hahn F, Belgsir EM, Lamy C. 2004a. On the mechanism of ethanol electro-oxidation on Pt and PtSn catalysts Electrochemical and in situ IR reflectance spectroscopy studies. J Electroanal Chem 563 81-89. 

Marinkovic et al. [50] have used in situ IR reflection spectroscopy to study adsorption of nitrate ions on Au(lll) electrodes. The ions were bonded to the gold surface via one of their oxygen atoms. Within the double-layer N03 formed contact ion pairs with hydronium ions. The extent of this process depended on the applied potential. 

All these results may be smmnarized in Fig. 12, where all the adsorbed species (identified by in situ IR Reflectance Spectroscopy) and intermediate products (analyzed by HPLC)" are shown. 

Some support for this arises from the observation by in situ IR reflection spectroscopy (70, 71) that chemisorbed CO is formed as a self-inhibiting species in the electrooxidation of HCOOH at, for example, Pt, where the main reaction sequence is... 

Immobilization immobilized aqueous phase in situ IR reflectance spectroscopy in situ IR transmission spectroscopy in situ NMR spectroscopy... 

The oxidation of ethanol is more difficult than that of methanol with the necessity to break the C-C bond to obtain its complete oxidation to CO2. It was observed by in situ IR reflectance spectroscopy that the dissociation of ethanol leads also to the formation of adsorbed CO [8]. This is the proof that the C-C bond can be, at least to some extent, broken at room temperature and that carbon dioxide can be obtained. However, the main oxidation products are... 

Dubau, L., Hahn, F., Coutanceau, C., et al. (2003). On the Structure Effects of Bimetallic PtRu Electrocatalysts Towards Methanol Oxidation, J. Electroanal. Chem., 554-555, pp. 407-415. Vigier, F., Coutanceau C., Hahn, R, etal. (2004), On the Mechanism of Ethanol Electro-oxidation on Pt and PtSn Catalysts Electrochemical and In Situ IR Reflectance Spectroscopy Studies,... 

Reaction products can also be identified by in situ infrared reflectance spectroscopy (Fourier transform infrared reflectance spectroscopy, FTIRS) used as single potential alteration infrared reflectance spectroscopy (SPAIRS). This method is suitable not only for obtaining information on adsorbed products (see below), but also for observing infrared (IR) absorption bands due to the products immediately after their formation in the vicinity of the electrode surface. It is thus easy to follow the production of CO2 versus the oxidation potential and to compare the behavior of different electrocatalysts. 

The different species formed by steps (18) to (20) or (18 ) to (20 ) have been detected by in situ infrared reflectance spectroscopy, and such dissociative steps are now widely accepted even if the exact nature of the species formed during (20) or (20 ) is still a subject of discussion. Several groups proposed the species (COH)3js as the main, strongly adsorbed species on the platinum surface, even though no absorption infrared band can be definitely attributed to (COH),, . However, the formyl-like species ( CHO), , . has been formally identified, since it gives an IR absorption band ataroimd 1690cm . ... 

When Desilvestro and Pons used in situ IR reflection spectroelectrochemistry to observe the reduction of C02 to oxalate at Pt electrodes in acetonitrile [83], two different forms of oxalate were observed. Similarly, Aylmer-Kelly et al. studied C02 reduction in acetonitrile and propylene carbonate at Pb electrodes [84], by using modulated specular electroreflectance spectroscopy. Subsequently, two radical intermediates were observed which they determined to be the C02 radical anion, C02, and the product of the radical anion and C02, the (C02)2 adduct (see Equations 11.9 and 11.10). Vassiliev et al. also studied the reduction of C02 in... 

The ATR technique is now routinely used for IR spectroscopy as it allows measurement of spectra for a variety of sample types with minimal preparation. The crystals employed are generally prismatic in shape, allowing contact of a flat surface with the sample. The ATR method was first adapted for HP IR spectroscopy by Moser [29-33], who realised that a conventional autoclave could easily be adapted for in situ IR spectroscopy by fitting an ATR crystal of cylindrical cross section. The technique developed by Moser is thus known as cylindrical internal reflectance (CIR) spectroscopy and high pressure cells based upon the CIR method have been commercialised by Spectra-Tech. A typical CIR cell is illustrated in Figure 3.8. 

Within the IR spectroscopy arena, the most frequently used techniques are transmission-absorption, diffuse reflectance, ATR, specular reflectance, and photoacoustic spectroscopy. A typical in situ IR system is shown in Fig. 7. Choosing appropriate probe molecules is important because it will influence the obtained characteristics of the probed solid and the observed structure-activity relationship. Thus, the probe molecules cover a range from the very common to the very rare, in order to elucidate the effect of different surfaces to very specific compounds e.g. heavy water and deuter-ated acetonitrile, CDsCN). The design of the IR cell is extremely important and chosen to suit the purposes of each particular study. For catalytic reactions, the exposure of catalytic metals must be eliminated in cell construction, otherwise the observed effect of the catalyst may not be accurate. 

In situ IR spectra were recorded using, either the Single Potential Alteration Iirfrared Reflectance Spectroscopy (SPAIRS), also called Linear Potential Sweep-Fourier Transform Infrared Reflectance Spectroscopy (LPS-FTIRS), or the Subtractively Normalized Interfacial Fourier Transform Infrared Reflectance Spectroscopy (SNIFTIRS). ... 

The increasing application of spectroscopic methods in electrochemistry has characterized the last decade and marked the beginning of new developments in electrochemical science [1]. Among these methods, in-situ infrared spectroscopy provides a very useful tool for characterizing the electrode-solution interface at a molecular level. First in-situ infrared (IR) electrochemical measurements were performed in 1966 [2] using the internal reflection form [3]. However, problems in obtaining very thin metal layers on the surface of the prisms used as IR windows, delayed the extensive application of in-situ IR spectroscopy until 1980, when the method was applied in the external reflection form [4]. The importance of this step does not need to be emphasized today. 

High quality IR spectra of different carbon surfaces were obtained by photo-thermal beam deflection spectroscopy (IR-PBDS) [123,124]. This technique was developed with the intention of providing an IR technique that could be used to study the surface properties of materials that are difficult or impossible to examine by conventional means. Recently, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) has been successfully applied to study the effect of different pretreatments on the surface functional groups of carbon materials [101,125-128]. Several studies aiming to improve the characterization of the carbon electrode surface and the electrode-electrolyte interface have been carried out using various in situ IR techniques [14,128-132]. The development of in situ spec-troelectrochemical methods has made it possible to detect changes in the surface oxides in electrolyte solutions during electrochemical actions. 

In situ electro-optical reflection is a very promising means for meeting this need. There are two such methods, internal and external reflection methods the latter includes specular reflection spectroscopy, ellip-sometry, IR reflection spectroscopy, and surface enhanced Raman scattering (SERS). 

Recent decades have witnessed spectacular developments in in-situ diffraction and spectroscopic methods in electrochemistry. The synchrotron-based X-ray diffraction technique unraveled the structure of the electrode surface and the structure of adsorbed layers with unprecedented precision. In-situ IR spectroscopy became a powerfiil tool to study the orientation and conformation of adsorbed ions and molecules, to identify products and intermediates of electrode processes, and to investigate the kinetics of fast electrode reactions. UV-visible reflectance spectroscopy and epifluorescence measurements have provided a mass of new molecular-level information about thin organic films at electrode surfaces. Finally, new non-hnear spectroscopies such as second harmonics generation, sum frequency generation, and surface-enhanced Raman spectroscopy introduced unique surface specificity to electrochemical studies. 

---