Kaido Tammeveski

Electrochemical reduction of oxygen on anthraquinone-modified glassy carbon electrodes in alkaline solution

Abstract The electrochemical reduction of oxygen on glassy carbon (GC) electrodes grafted with anthraquinone (AQ) has been studied using the rotating ring–disk electrode technique. Grafting was achieved by the electrochemical reduction of the corresponding diazonium salt and the effect of AQ surface concentration on the kinetics of oxygen reduction has been investigated. The two-electron reduction of oxygen to hydrogen peroxide was observed for all the quinone-modified electrodes studied and the catalytic activity of the electrodes for O 2 reduction was dependent on the AQ surface concentration. The kinetic parameters of oxygen reduction on GC/AQ electrodes in 0.1 M KOH were determined as a function of AQ surface concentration considering a surface redox catalytic cycle model for quinone-modified electrodes. The rate constant of the chemical reaction between the semiquinone radical anion of AQ and molecular oxygen has been determined.

SUPEROXIDE ELECTRODE BASED ON COVALENTLY IMMOBILIZED CYTOCHROME C : MODELLING STUDIES

We have recently described an optimised electrode for the detection of enzymatic and cellular superoxide (O2*-) production based on cytochrome c immobilized covalently at a surface-modified gold electrode and applied this system to the study of free radical production by activated human glioblastoma cells. In this paper we report the development of a mathematical model for the O2*- electrode responding to enzymically produced O2*- which should enable the determination of absolute concentrations of O2*- in biological systems when this electrode is employed for direct, real-time monitoring of free radical release and interactions.

Electrochemical reduction of oxygen on thin-film Pt electrodes in 0.1 M KOH

The electroreduction of oxygen has been studied on thin-film platinum using the rotating disk electrode technique. The kinetic parameters of oxygen reduction were determined for Pt films over the range of thickness from 1 to 50 nm. The kinetics of oxygen reduction were found to be slightly influenced by the platinum film thickness.

Electrochemical reduction of oxygen on thin-film Au electrodes in acid solution

The reduction of oxygen has been studied on thin-film gold electrodes using the rotating disk electrode (RDE) technique. Thin films of gold were prepared by vacuum evaporation onto glassy carbon and highly oriented pyrolytic graphite substrates. The surface morphology of the films was examined by atomic force microscopy. The kinetic parameters of O2 reduction have been determined and a Tafel slope of (−112±8)mVdec−1 was observed. The specific activity of the electrodes was almost independent of film thickness.

Kinetics of Oxygen Reduction on Quinone-Modified HOPG and BDD Electrodes in Alkaline Solution

The kinetics of oxygen reduction on boron-doped diamond (BDD) and highly oriented pyrolytic graphite (HOPG) electrodes modified with anthraquinone and phenanthrenequinone have been studied using the rotating disk electrode technique. The electrode surfaces were grafted by the electrochemical reduction of the corresponding diazonium salts. The kinetic parameters of oxygen reduction on the modified electrodes in 0.1 M KOH were determined using a surface redox-catalytic cycle model for quinone-modified electrodes. The results obtained further confirm the validity of the model used.

Oxygen electroreduction on titanium-supported thin Pt films in alkaline solution

Abstract The electrochemical reduction of oxygen at thin Pt films prepared on titanium substrate has been studied in alkaline solution. Tafel plots with two different slope regions were observed for oxygen reduction in 0.1 M KOH. At low current densities the slope was around − 60 mV dec −1 , whereas at high current densities the slope was varying between −260 and −490 mV dec −1 . The oxygen reduction behaviour at Pt/Ti electrodes was qualitatively the same in comparison to that of Pt/GC electrodes. Cyclic-voltammetric experiments revealed that the potential of the hydrogen adsorption-desorption peaks and the platinum oxide reduction peak shifted towards positive potentials with the increasing Pt film thickness in 0.1 M KOH and 0.5 M H 2 SO 4 . The coverage of platinum surface with oxygen-containing species ( Θ ox ) was found to be dependent on Pt film thickness. Θ ox plays an important role in determining the oxygen reduction kinetics at platinum electrodes.

Electroreduction of oxygen on gold nanoparticle/PDDA-MWCNT nanocomposites in acid solution

The electrochemical reduction of oxygen has been studied on gold nanoparticle (AuNP)/poly(diallyldimethylammonium chloride) (PDDA)-multi-walled carbon nanotubes (MWCNTs) modified glassy carbon (GC) electrodes in 0.5 M H2SO4 using the rotating disk electrode (RDE) technique. The AuNP/PDDA-MWCNT catalysts were prepared using an electrostatic layer-by-layer (LBL) technique. The composite electrode was electrochemically characterized by cyclic voltammetry in an O2-free electrolyte. The oxygen reduction behaviour of these electrodes was compared with that of a PDDA-MWCNT/GC electrode. The AuNP/PDDA-MWCNT catalysts showed a remarkable electrocatalytic activity towards O2 reduction in acid media. The half-wave potential of O2 reduction on the AuNP/PDDA-MWCNT catalyst shifted more than 200 mV to more positive potentials as compared to that of a PDDA-MWCNT/GC electrode. The kinetic parameters of O2 reduction were determined and the specific activity of the hybrid electrodes was higher than that of bulk gold.

Electrochemical Reduction of Oxygen on Multiwalled Carbon Nanotube Modified Glassy Carbon Electrodes in Acid Media

The electrocatalytic reduction of oxygen has been studied on multiwalled carbon nanotube (MWCNT) modified glassy carbon (GC) electrodes in 0.5 M H 2 SO 4 solution using the rotating disk electrode technique. The oxygen reduction behavior of oxidatively pretreated and untreated MWCNT modified GC electrodes was compared. The results obtained indicate that the electrocatalytic properties of untreated MWCNTs toward O 2 reduction in acid media are noticeably better than that of pretreated MWCNTs. This effect is caused by catalyst impurities which remain in the nanotubes prepared by chemical vapor deposition and can be largely removed by treatment in acids.

Substituent effects on the electrocatalytic reduction of oxygen on quinone-modified glassy carbon electrodes

The reduction of oxygen catalysed by two sulfur-containing derivatives of anthraquinone has been investigated. The quinones were chemically grafted to a glassy carbon electrode surface and the oxygen reduction reaction in alkaline solution followed a two-electron pathway yielding hydrogen peroxide. The mechanism proposed corresponds to an electrochemical–chemical (EC) reaction where the semiquinone radical anion electrochemically formed reacts chemically with oxygen. The influence on reactivity of electron withdrawing groups present in the quinone molecules has been studied and it is shown that there is an unexpected small dependence between reactivity and standard potential of the grafted quinones. It is shown that steric effects appear important in determining their electrocatalytic properties.

The reduction of oxygen on Pt-TiO2 coated Ti electrodes in alkaline solution

The electrochemical reduction of was studied on and coated Ti electrodes using the rotating disk electrode technique. The coatings were prepared by the thermal decomposition method in the Pt composition range 10–100 wt %. Tafel plots with two distinct slope regions were observed for the reduction of on the electrodes of high Pt content. The electrocatalytic activity toward oxygen reduction decreased remarkably for the electrodes containing less than 35% Pt. The activity decrease was explained by an electrode resistance increase at lower Pt contents. Cyclic voltammetric measurements revealed that the electrode behavior was strongly dependent on the Pt content in the coating. The surface of electrodes was characterized by X‐ray diffraction, scanning electron microscopy, and X‐ray photoelectron spectroscopy.