Ki-Hyung Chjo

Thin Titanium Dioxide Film Electrodes Prepared by Thermal Oxidation

Effects of temperatures, at which TiO 2-x electrodes were prepared by thermal oxidation from titanium sheet metals, as well as platinum loading, on electrochemical and photoelectrochemical properties have been studied and the results are reported. Titanium dioxide electrodes prepared at higher temperatures were found to have slightly more negative flat-band potentials and significantly higher donor densities than their low temperature counterparts. Platinum loading showed a similar effect to a lesser extent

Oxygen reduction at Co(II)2-disalophen modified carbon electrodes

Reduction of dioxygen in both aqueous and nonaqueous solutions has been receiving a great deal of attention due to its implications in practical applications such as fuel cells and batteries, as well as in biological reactions. Oxygen reduction at a dinuclear Co(II)-Schiff-base complex, Co(II){sub 2}-3,3{prime},4,4{prime}-tetra(salicylidene imino-1,1{prime}-biphenyl tetrahydrate) [Co(II){sub 2}-disalophen; Co(II){sub 2}-DSP {center_dot} 4H{sub 2}O], modified carbon electrodes has been studied and results thereof are reported. The absorbed complex is shown to have a large catalytic effect for oxygen reduction. The oxygen reduction at the Co(II){sub 2}-DSP {center_dot} 4H{sub 2}O modified carbon electrodes is reasonably reversible in alkaline solutions with an apparent number of electrons transferred of around one and an estimated exchange rate constant of about 0.04 cm/s. The strong catalytic activity is explained by the formation of a reversible adduct with oxygen followed by reduction of Co(III) in the adduct. The cyclic voltammetric and chronoamperometric experimental results suggest that the first electron transfer should be a rate limiting step.

Electrocatalytic reduction of dioxygen by quadruply aza bridged closely interfaced cofacial bis(5,10,15,20-tetraphenylporphyrin)s in various pH solutions

Abstract The electrocatalytic reduction of dioxygen is investigated by cyclic voltammetry and chronoamperometry at a glassy carbon electrode and a carbon microelectrode adsorbed with cobalt porphyrins in dioxygen-saturated aqueous solutions of various pH. The reduction potential ( E p ) of dioxygen at chemically modified electrodes shows dependence on pH. Electrochemical reduction of dioxygen at monomeric Co-1 or dimeric Co 2 -2 modified electrodes establishes a pathway of 2e − reduction to form hydrogen peroxide, but it carries out 4e − reduction of dioxygen to water at the electrode adsorbed with dimeric Co 2 -3 or Co 2 -4 in all pH solutions. The electrocatalytic pathway of dioxygen reduction by cofacial biscobalt porphyrins is independent of pH, but the E p of dioxygen reduction is dependent on pH. Theelectrochemical reduction of dioxygen is irreversible and diffusion controlled.