Mechanistic Determination Using Arrays of Variable-Sized Channel Microband Electrodes:  The Oxidation of Ascorbic Acid in Aqueous Solution

Abstract

“Two-dimensional voltammetry” using arrays of variable-sized gold channel microband electrodes in combination with variable flow rate measurements together with independent gold rotating disk electrode (RDE) data is applied to characterize the oxidation mechanism of l-ascorbic acid (AH2) to dehydro-l-ascorbic acid in aqueous solutions. At pH 2.1 and very low mass transport conditions the reaction is consistent with a CECE mechanism, while at higher mass transport conditions an ECfastCE mechanism is followed. At pH 6.7, the results are again consistent with an ECE mechanism. The following mechanism is proposed: AH2 ⇌ AH- + H+ (k CEE), AH- → AH• + e, AH• → A• - + H+ (k ECE), A• - → A + e (CECE); AH2 ⇌ AH2 + + e, AH2 + → AH• + H+(fast), AH• → A• - + H+ (k ECE), A• - → A + e (ECfastCE); where, only the first pathway applies at pH 6.7, AH- being the starting species. Values of 3.4 × 103 s-1 and 500 s-1 are found for the rate constants k CEE and k ECE, respectively.

Photo-induced redox catalysis for proton reduction to hydrogen with homogeneous molecular systems using rhodium-based catalysts

“…8). Then A •− is able to disproportionate in weakly acid aqueous solution (at pH around 5.0) [108,109] into the initial HA − and the dehydroascorbic acid (A) that can further decompose via a proton-catalyzed hydration of its carbonyl groups [86]. Nonetheless, the A species is a good electron acceptor and is also capable to turn back to HA − by re-oxidizing the reduced PS or the reduced Cat, contributing to the deactivation of the photocatalytic process.…”

Channel Microband Electrode Arrays for Mechanistic Electrochemistry. Two-Dimensional Voltammetry: Electrode Kinetics

“…The use of both variable electrode size and convection implies that each electrode has its own characteristic kinetic window at a particular¯ow rate, so the joint combination of variable¯ow and electrode size provides an electrochemical tool capable of covering a wide range of rate constants, and speci®cally has been shown to be very sensitive to the determination of reaction mechanisms [1±3]. In particular the application to characterize ECE, ECEE, EC H and DISP2 reactions [1] as well as the more complicated mechanisms accompanying the oxidation of ascorbic acid in water [2] and the generation of radical cations in nonaqueous media containing nucleophiles [3] have been explored.…”

Use of organic reductants to lower brightener consumption in acid copper electroplating bath utilising catalytic anodes

“…Multistage oxidation: the anodic oxidation of Lascorbic acid has been studied on a range of different anodes and mechanisms involving several intermediate steps have been proposed [13][14][15][16][17] in acid media (see Fig. 9).…”