Diffusion layer imaging: spatial resolution of electrochemical concentration profiles

Abstract

12) Schmldt, D. E.; Giese, R. W.; Conron, D.; Karger, 8. L. Anal. Chem. lQB0. 52. 177-182. ----, --. (13) Pinkerton, T. C.; Hagestam, I. H. US. Patent, 6646 153, 1984. (14) Bethell, G. S.; Ayerer, J. S.; Hancock, W. S.; Hearn, M. T. J . 8/01. Chem. 1979, 254, 2572-2574. (15) Lasson, P. 0.; Glad, M.; Hasson, L.; Mansson, M. 0.; Ohlson, S.; Mosbach, U. (21) Haroon, V.; Keith, D. A. J . Chromatogr. 1983, 276, 445-450. (22) Lunde, P. K. M.; Rane, A.; Yaffe, S. J.; et al. C/h. Pharm. Ther. 1970, (23) Miller, T. D.; Plnkerton, T. C. Anal. Chim. Acta, In press. Sir:We report here a spectrophotometric technique for determining concentration vs. distance profiles of absorbing solution species generated at an electrode surface. The technique can accurately describe diffusion layers as thin as 8 pm, after only 50 ms of electrolysis. In this paper, we describe the apparatus and its performance and discuss its potential for providing new information about mass transport and reaction mechanisms. The fundamental importance of mass transfer to electrochemistry has spawned a variety of theoretical and experimental examinations into diffusion (1, 2), convection (3-51, and migration (6) as mechanisms for the transport of redox species to an electrode. For several well-defined mass transport situations, the Faradaic current may be predicted from theories of diffusion and hydrodynamics, but in many cases solutions are not readily available. Diffusion to microelectrode arrays (7,8), mass transport in flowing streams (9, IO), and mixed convection/migration conditions are examples of cases where concentration vs. distance profiles are not available, and the Faradaic current is not accurately predictable from theory. Several approaches have been pursued to experimentally observe concentration-vs. distance profiles near an electrode, including interferometric methods (10-15) based on refractive index gradients near an electrode and on UV-vis absorption by electrogenerated species (16-18). The present approach is a spatidy resolved UV-vis absorption measurement which permits concentration vs. distance profiles to be obtained with better resolution and shorter time scales than those from previous methods. The cross section of a beam passing parallel to a planar electrode surface is magnified and imaged onto a photodiode array detector. Each diode samples a discrete distance from the electrode, and Beer's law may be used to directly determine a spatially resolved concentration profile.The cell, electrodes, and chemical systems were identical with those described previously for diffractive spectroelectrochemistry (19). Trianisylamine (TAA) in acetonitrile was oxidized at a platinum electrode to TAA+. at +0.8 V vs. aqueous SCE. The diffusion coefficient of TAA (1.25 X 10" cm2/s) and molar absorptivity for TAA+. (11OOO & 200 M-' cm-' , at 633 nm) have been reported previously (19). The optical apparatus shown in Figure 1 consists of a 2Ox magnifier producing an image of the beam cross section on the face of a 1024 element photodiode array. L1 ...

Charge neutralization process of mobile species developed during potentiodynamic conditions. Part 1: Theory

“…Because of this, several electrochemical techniques have been developed to render information associated with the transference of electrons and the transport phenomena of chemical species into this zone [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Similarly, many theoretical studies have been performed to consider processes related to the movement of reactants and products into the solution as well as to the kind of reaction that occurs in the system [1,2,[16][17][18][19][20][21][22][23][24][25][26][27][28].…”

Application of photothermal deflection spectroscopy to electrochemical interfaces

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Visualization of Electrochemical Reactions by Redox-dependent Quenching of Photoluminescence from ZnS-AgInS2 Solid Solution Semiconductor Nanoparticles

“…Herein, we demonstrate a new means to visualize electrochemical reactions by the fluorescence quenching of the ZnS-AgInS 2 solid solution (ZAIS) NPs caused by electron transfer as a probe. In situ techniques to observe an electrochemical diffusion layer had been reported using a specially modified microscopy with diode array detector, [18][19][20] a confocal Raman microscopy, [21][22][23][24] and recently by a scanning electron microscopy with an x-ray spectrometer. 25 The present method detecting the variation in polarity can, in principle, cover many types of redox reactions if semiconductor NPs with an appropriate energy level and polarity are selected.…”