The effect of anion adsorption on the kinetics of the Fe3+/Fe2+ reaction on Pt and Au electrodes in HclO4

Pseudo-Single-Crystal Electrochemistry on Polycrystalline Electrodes: Visualizing Activity at Grains and Grain Boundaries on Platinum for the Fe2+/Fe3+ Redox Reaction

“…. 58,60 It is important to point out that the local variation in activity visualized by SECCM would have some impact on macroscopic CV measurements of heterogeneous ET on polycrystalline platinum. Electrode kinetic measurements on polycrystalline platinum tend to implicitly assume a uniform electrode surface 45,46,56,57 and evidently, at least for the case of Fe 2+ /Fe 3+ (and perhaps other reactions), this is not always appropriate.…”

Mapping the dynamics of reversible and irreversible heterogeneous electron transfers under steady-state conditions by the phase-space method

“…It is well known that chloride, bromide, or sulfate influences the reaction rates [25,26]. A catalytic effect is observed because these anions adsorb on the metal electrode surface, and thereby reduce the electrostatic repulsion of iron ions from the electrode or provide a bridge for a faster electron transfer (inner-sphere catalysis) [27,28]. In the absence of strongly adsorbed anions, the standard rate constant is low, about 9 · 10 À6 and 5 · 10 À5 cm.s À1 for polycrystalline platinum and gold, respectively [27].…”

“…A catalytic effect is observed because these anions adsorb on the metal electrode surface, and thereby reduce the electrostatic repulsion of iron ions from the electrode or provide a bridge for a faster electron transfer (inner-sphere catalysis) [27,28]. In the absence of strongly adsorbed anions, the standard rate constant is low, about 9 · 10 À6 and 5 · 10 À5 cm.s À1 for polycrystalline platinum and gold, respectively [27]. Indeed, in purified perchloric acid solutions very slow kinetics are observed in the absence of chloride catalysis [29].…”

Electrochemistry of Fe3+/2+ at highly oriented pyrolytic graphite (HOPG) electrodes: kinetics, identification of major electroactive sites and time effects on the response

“…2,3,18 Here, we present a study of the Fe 3+/2+ redox couple in aqueous solution, which is known to have much slower ET kinetics, 30 but is still regarded as an outer-sphere process, 29 although one that can be promoted (enhanced) by some adsorbed anions at metals such as platinum. 31,32 Thus, with careful experimental design, this is a very attractive redox system with which to make kinetic comparisons on different electrodes.…”