Situ Optical Studies

Much of the earlier studies of the anodic layer with ellipsometry were carried out by Bockris and his group. Reddy, Genshaw, and 

Bockris followed the formation of the anodic film on Pt using ellipsometry. Whereas oxygen adsorption begins at Eu = 0.8 V, these workers found no evidence of such in their ellipsometric measurements below 0.95 V. At more anodic potentials, distinctive changes of A were found and attributed to the formation of the oxide film. These workers assumed that real component 

In later work using measurements of the change of reflectance (AR) as well as A and (/ , however, Kim, Paik, and Bockris found that the optical constants of the film on Pt were nearly independent of electrode potential Eli between 0.8 and 1.6 V with only the thickness of the film increasing nearly linearly with potential. Apparently the earlier measurements of Reddy et (144,145) sensitivity to follow the film formation when it was a 

A number of other workers also have examined the anodic layer on Pt with ellipsometry and specular reflectance spectroscopy. In contrast to Kim et several of these researchers have found evidence for 

Complex Refractive Index (h = n- Ik) for the Oxide Layer on Pt Formed at Eh = 1.4-1.6 V in Acid Electrolytes, as Determined by Various Workers  

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St. Jean, M., M. Menant, N. Hy Hau, C. Rigaux, and A. Metrot. 1983. In situ optical study of H2S04-graphite intercalation compounds. Synth. Metals 8 189-193. 

V. L. Berkovits et al.. Chemical and Photochemical Processes in Sulfide Passivation of GaAs (100), In Situ Optical Study and Photoemission Analysis, J. Vac. Sci. Technol. A 1998, 16, 2528-2538. 

M. B. Pomfret, J. C. Owrutsky, and R. A. Walker, Ann. Rev. Anal. Chem., 3, 151 (2010). In Situ Optical Studies of Solid-Oxide Fuel Cells. 

Yagi I, Lantz JM, Nakabayashi S, Corn RM, Uosaki K (1996) In situ optical second harmonic generation studies of electrochemical deposition of tellurium on polycrystalline gold electrodes. J Electroanal Chem 401 95-10... 

Optical second harmonic generation from electrode surfaces is employed in situ to study the... 

Shang et al. (61) used microemulsion polymerization to synthesize MWCNT-PMMA composites for gas sensor applications. Better dispersion, enhanced electrical conductivity and better sensor response was observed for in-situ fabricated composites compared to composites prepared by solution mixing. Ma et al. (62) performed in-situ polymerization of MWCNT-PMMA composites in the presence of an AC electric field to study dispersion and alignment of MWCNT in PMMA matrix induced by the electric field. Experimental evidences from in-situ optical microscopy, Raman spectroscopy, SEM and electrical conductivity showed that both dispersion and alignment qualities were significantly enhanced for oxidized MWCNT compared to pristine MWCNT. 

Shekunov, B.Y. Grant, D.J.W. In situ optical interferometric studies of the growth and dissolution behavior of paracetamol (acetaminophen). 1. Growth kinetics. J. Phys. Chem. B 1997,101 (20), 3973-3979. 

The use of infrared spectroscopy in the Earth and environmental sciences has been widespread for decades however, until development of the attenuated total reflectance (ATR) technique, the primary use was ex situ material characterization (Chen and Gardella, 1998 Tejedor-Tejedor et al., 1998 Degenhardt and McQuillan, 1999 Peak et al., 1999 Wijnja and Schulthess, 1999 Aral and Sparks, 2001 Kirwan et al., 2003). For the study of environmental systems, the strength of the ATR-Fourier transform infrared (FTIR) technique lies in its intrinsic surface sensitivity. Spectra are collected only from absorptions of an evanescent wave with a maximum penetration depth of several micrometers from the internal reflection element into the solution phase (Harrick, 1967). This short optical path length allows one to overcome any absorption due to an aqueous phase associated with the sample while maintaining a high sensitivity to species at the mineral-water interface (McQuillan, 2001). Therefore, ATR—FTIR represents a technique capable of performing in situ spectroscopic studies in real time. 

This chapter discussed the application of the electro-optical reflection method in the in situ observation of the adsorption and desorption of bioactive substances at an electrode surface acting as a simple model of charged sites at a biosurface. This method should find extensive application in various bioelectrochemical fields as a potent means of surface analysis. Electrode surfaces, though much simpler than biosurfaces, still provide data reflecting actual occurrences at biosurfaces in some respects. Electro-optical studies on the behavior of bioactive substances at electrode surfaces should provide some indication of how such substances behave at biosurfaces. 

In order to get answers to these questions, the ability to better characterize catalysts and electrocatalysts in situ under actual reactor or cell operating conditions (i.e., operando conditions) with element specificity and surface sensitivity is crucial. However, there are very few techniques that lend themselves to the rigorous requirements in electrochemical and in particular fuel cell studies (Fig. 1). With respect to structure, in-situ X-ray diffraction (XRD) could be the method of choice, but it has severe limitations for very small particles. Fourier transform infra red (FTTR), " and optical sum frequency generation (SFG) directly reveal the adsorption sites of such probe molecules as CO," but cannot provide much information on the adsorption of 0 and OH. To follow both structure and adsorbates at once (i.e., with extended X-ray absorption fine stmcture (EXAFS) and X-ray absorption near edge stmc-ture (XANES), respectively), only X-ray absorption spectroscopy (XAS) has proven to be an appropriate technique. This statement is supported by the comparatively large number of in situ XAS studies that have been published during the last decade. 16,17,18,19,20,21,22,23,24,25 highly Versatile, since in situ measme-... 

The influence of the structure of the ad-atom layers on the reduction of oxygen was examined by using in situ optical and scaiming probe microscopies. With these techniques reliable information on the structure of the ad-atom layers can be obtained during the course of oxygen or hydrogen peroxide reduction. In most systems studied, the UPD adlattice structures are not affected by the presence of molecular oxygen in solution. On the basis of... 

This procedure involves, however, some uncertainty, mainly because electrochemical methods give only direct, electrical information on the surface charge transfer reactions. Much effort has been directed to in situ optical spectroscopic methods to study the electronic properties of these surface layers and to study the interactions of the oxygen species with Pt (see Section 4.2). 

Despite the extensive studies of the anodic layers on Pt with various ultraviolet-visible optical methods, they have not provided a clear indication of the electronic or structural properties of the layers. Rather these optical methods have been more than just another form of readout to complement the electrochemical measurements of charge and current response of the layer to potential and time. Vibrational spectroscopic data from infrared and Raman measurements would be more helpful in establishing the nature of the layers but it is difficult to use these techniques to study metal-electrolyte and similar interfaces because of solvent interference and sensitivity problems. A noteworthy exception is the quite successful in situ use of Raman spectroscopy to study the electrochemically formed oxide layers on silver by Kotz and Yeager. In the instance of silver electrodes, there is a large surface enhanced Raman effect and the signal-to-noise ratio is not a problem. Unfortunately this is not the situation with other metal surfaces such as Pt. Even so, with improved instrumentation there is hope that in situ Raman studies of the anodic layers on Pt will become practical. 

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