Determination of the visible spectra of electrode reaction products in strongly absorbing media by diffusion-controlled chronoabsorptometry

Abstract

Chronoabsorptometry under diffusion-controlled conditions has been applied to determination of the difference in molar absorptivity between electrode reaction products and reactants. The technique allows complete determination of the ultraviolet-visible spectra of reaction products that are stable on the time scale of a few hundred milliseconds. The technique was implemented with a reflectance cell that employs quartz light pipes to minimize optical absorbance of the bulk solution without obstructing the current path between counter and working electrodes. The spectrum of one-electron oxidized chloro-(5, LO, 15,20-tetraphenylporphinato)Fe(III) is determined with the new technique and compared with that obtained by conventional thin-layer spectroelectrochemistry.Key rvords: spectroelectrochemistry, chronoabsorptometry, thin-layer spectroelectrochemistry.RCsum6 : On a applique la chronoabsorptomCtrie sous des contrales par diffusion h la determination de la difference dlabsorptivitC molaire entre les rCactifs et les produits de la reaction h I'tlectrode. La technique permet de faire une determination complttte des spectres UV-visibles des produits rCactionnels qui sont stables h I'Cchelle de temps de quelques centikmes de millisecondes. La technique a CtC appliquee h l'aide d'une cellule de reflectance qui fait appel h des conduits de lumittre en quartz pour minimiser I'absorption optique de I'ensemble de la solution sans interferer avec le champ du courant entre les electrodes de rCfCrence et de travail. Faisant appel h cette technique, on a determine le spectre du chloro-(5,10,15,20-tCtraphCnylporphinate)Fe(III) oxydt par un electron et on I'a compare h celui obtenu par la technique conventionnelle de spectroClectrochimie en couche mince.Mots elks : spectro~lectrochirnie, chronoabsorptomCtrie, spectroClectrochimie en couche mince.[Traduit par la rCdaction] Determination of the uv-visible spectra of electrochemical reduction or oxidation products of highly coloured species is most frequently accomplished using thin-layer spectroelectrochemical techniques. The short optical pathlength in thin-layer cells facilitates high optical throughput, which is important in maintaining good signal-to-noise ratios. There is, however, a finite time required to achieve complete electrolysis of the thin-layer cavity due to mass transport limitations (1). In practice, even this theoretical minimum time requirement is rarely achieved because of the high solution resistance associated with the thin-layer cavity (2). This delays the onset of electrolysis at points in the thin-layer cavity positioned furthest from the counter electrode with respect to those positioned closer to the counter electrode. The effect is particularly severe in highly resistive nonaqueous media, and increases as the working electrode dimensions increase. Thin-layer techniques are thus not well suited to determining the spectra of electrochemically generated products of limited stability. Chronoabsorptometry under conditions of semi-infinite linear d...

Facile Determination of the Spectra of Unstable Electrode Products Using Simultaneous Fiber-Optic Chronoabsorptometry and Chronoamperometry

“…The methodology employed in this work is based on established electrochemical principles. The theory , and application , of chronoabsorptometry have been reported. In our continuing efforts to improve the spectroelectrochemical methodology for the ready generation and detection of reaction intermediates, we have employed the fundamental mathematics of chronoabsorptometry to develop readily accessible instrumentation to generate UV−vis absorption spectra of intermediates not observable by current techniques that employ OTTLE or other spectroelectrochemical cells.…”

“…The advantages of this new methodology (e.g., using eqs and ) include the following: (i) there is no arbitrary spectral subtraction of the starting material’s spectral features to enhance the spectrum of the intermediate, (ii) the approach is independent of knowledge of the accurate path length of the electrochemical cell, and (iii) quantitative knowledge of the absorptivity values facilitates assignment of the spectra features for the electrode species. In previous work by others, an approach using eq was applied by measuring ε B (λ) values one at a time over a given spectral window; , this approach proved to be quite tedious, requiring >60 manual trials at each separate λ. To the best of our knowledge, eq has not been used previously to yield absorptivity versus wavelength data from a single experiment.…”

In Situ Spectroscopic Determination of Faradaic Efficiencies in Systems with Forced Convection under Steady State: Electroreduction of Bisulfite to Dithionite on Gold in an Aqueous Electrolyte

“…Interest in this research group has been focused on the development of in situ and on line spectroscopic techniques capable of providing quantitative information regarding both the identity of electrogenerated products and the potential dependence of their specific faradaic yields under well-defined hydrodynamic conditions. [5][6][7][8][9] Closely related spectroelectrochemical techniques for monitoring solution-phase species in the UV-visible range have also been reported in other laboratories both under stagnant 10,11 and, more recently, forced convection conditions using a channel-type cell. 12 This work illustrates the use of UV-visible spectroscopy at both a rotating disk electrode (RDE), in a reflection absorption geometry, and downstream from a channel-type electrode, in the transmission mode, to determine specific faradaic yields of dithionite (S 2 O 4 2-) generation from bisulfite on Au electrodes as a function of the applied potential.…”

“…Interest in this research group has been focused on the development of in situ and on line spectroscopic techniques capable of providing quantitative information regarding both the identity of electrogenerated products and the potential dependence of their specific faradaic yields under well-defined hydrodynamic conditions. − Closely related spectroelectrochemical techniques for monitoring solution-phase species in the UV−visible range have also been reported in other laboratories both under stagnant , and, more recently, forced convection conditions using a channel-type cell …”

Spectroelectrochemistry: In s itu UV ‐visible Spectroscopy

“…porphyrins) can be examined using reflectance and time-resolved difference spectroscopy. The light was reflected off the electrode using quartz rods mounted some distance away and at an angle of 45 • to the normal [165].…”