Voltammetric application of electromodulated electroreflection absorption spectroscopy: electroreflectance voltammetry as an in situ spectroelectrochemical technique

Abstract

It has been demonstrated that the voltammetric in situ application of electromodulated UV-vis reflectance spectroscopy, electroreflectance (ER) voltammetry, is a powerful tool with which to analyze the electrode reaction of an adsorbed species on an electrode surface. The ER response, which in fact originates from the absorbance change with ac modulation of the electrode potential, was theoretically analyzed and simulated as a function of electrode potential. The results of the theory and simulation were compared to the electrode reaction of Nile Blue A adsorbed on a pyrolytic graphite electrode surface. The resulting ER voltammetry was responsive only to the faradaic processes of Nile Blue A adsorbed on a pyrolytic graphite electrode, and its turnover reaction rate was determined to be in the range of 60-120 5-1. It was revealed through ER measurements that the electronic structure as well as the redox reaction mechanism of the adsorbed Nile Blue A on a graphite electrode were significantly different from those of the native dye. IntroductionThe recent development of spectroelectrochemistry has received a great deal of attention. The combined use of in situ spectroscopic techniques and conventional methods has afforded us a detailed understanding of electrode processes on a molecular level.' A variety of structural and mechanistic information is provided, depending on the method of spectroscopy. Infrared reflection absorption spectroscopy (IRRAS) and Raman scattering (RS) spectroscopy offer information about the structural aspects in the vibrational mode, while ultraviolet-visible (UV-vis) absorption spectroscopy offers similar information in an electronic mode. A body of work on the electrode process using UV-vis absorption has been carried out to measure in situ the spectra of species in the solution phase, among which the optically transparent thin-layer electrode (OTTLE) is most widely utilized.2 Attempts have also been made to measure the spectra of the species in the vicinity of the electrode interface by using the internal reflection method with an optically transparent ele~trode.~The reflection method in UV-vis mode to characterize solid surfaces, often referred as electroreflectance (ER), has developed in solid-state physicse4t5 The method has been widely used in the studies of the electronic band structure of semiconductors. In this method, the reflectance change a t the solid surface due to the perturbation of dielectric properties of the surface is detected as a function of the surface electronic field of the solid.The ER technique has also been applied to metal electrode surfaces combined with conventional electrochemical methods where a change in surface charge causes a change in reflectance. For example, Hinnen and her

Observation of Electron Transfer between a Silver Electrode and Putidaredoxin Using Electromodulated Reflectance Spectroscopy

“…For our detection sensitivity (DR/R Ç 10 06 ), it is feasible to follow these The differential reflectance measures the difference in reflection between the case when a protein layer is present on charge transfer reactions even at submonolayer quantities of Pdx adsorbate since the difference in the absorption spectra between the two redox forms, Pdx ox and Pdx red , is substantial. Similar optical detection of faradaic transitions has been reported recently for adsorbed organic dyes (22)(23)(24)(25), metal porphyrins (27), and heme proteins (10,11,26).…”

Electron-Transfer Rate in Potential-Modulated Redox Reactions with Electro-Active Optical Waveguides

“…Spectroelectrochemical techniques are particularly useful to mitigate those difficulties by focusing solely on the faradaic process and avoiding the strong non-faradaic electrical background. [10][11][12][13][14][15][16][17][18][19][20][21][22] Based on spectroscopic optical changes that typically accompany a redox event, it is usually possible to select the wavelength of a probing light beam to uniquely capture the optical changes associated with the faradaic process and is immune to the presence and motion of background ions in the electric double layer.…”

Specular Reflection Studies on the Adsorption of Quaternary Ammonium Ions, Alcohols and Flavin Mononucleotide on a Glassy Carbon Electrode Surface

“…Cell construction and measuring techniques were essentially the same as already described. 5 The light beam from a He-Ne laser (Toshiba LHG-3221, 2 mW), with a wavelength of 633 nm and perpendicular polarization was directed at the working electrode surface at an incidence angle of SCIENCES OCTOBER 1993. VOL_ 9…”

“…Electromodulated electroreflection absorption spectroelectrochemistry technique was carried out to characterize adsorbed species on a carbon electrode. 5,6 This technique has been found useful for analyzing electrode reactions of adsorbed species having large extinction coefficients, but may not be applicable to the study of dynamic adsorption-desorption behavior of UVvisible transparent substances. Specular reflection measurement in the visible region has been shown to facilitate the in situ study of electrosorption of various substances on solid metal electrodes, this being due not only to high sensitivity toward adsorption but also to simplicity of application.…”