Ave Sarapuu

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.

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.

Electrocatalysis of oxygen reduction on heteroatom-doped nanocarbons and transition metal–nitrogen–carbon catalysts for alkaline membrane fuel cells

Over the last decade, great progress has been made in the development of non-precious metal catalysts for the electrochemical oxygen reduction reaction (ORR). Among these, heteroatom-doped carbon nanomaterials and transition metal–nitrogen–carbon (M–N–C) catalysts are especially advantageous in an alkaline environment, showing high electrocatalytic activity for the ORR and good durability. Over the past few years, substantial achievements have also been made in improving the performance of anion exchange membrane fuel cells (AEMFCs) and the commercialisation of these devices has emerged as a viable option. This review article provides an outline to the most relevant studies of the ORR on heteroatom-doped nanocarbons and M–N–C type catalysts in alkaline media. In addition, an overview of the studies employing these materials as cathodes in AEMFCs is presented. A separate section is devoted to the results obtained with alkaline direct methanol and ethanol fuel cells. Further perspectives in the field of AEMFC research and development are also highlighted.

Electrocatalysis of oxygen reduction on glassy carbon electrodes modified with anthraquinone moieties

Anthraquinone groups were electrochemically grafted to glassy carbon (GC) electrodes via methylene linker to study the oxygen reduction reaction (ORR) in alkaline medium. Two different anthraquinone derivatives, 2-bromomethyl-anthraquinone or 2-chloromethyl-anthraquinone, were used to modify the GC electrode surface. Several modification conditions encompassing potential cycling and electrolysis at a fixed potential were employed in order to vary the surface concentration of MAQ groups (ΓMAQ) and to study the dependence of the O2 reduction behaviour on electrografting procedure. Cyclic voltammetry confirmed the presence of anthraquinone moieties attached to the GC electrode and ΓMAQ varied in the range of (0.5–2.4) × 10−10 mol cm−2. Oxygen reduction was studied on MAQ-modified GC electrodes of various surface coverage using the rotating disc electrode (RDE) and rotating ring-disc electrode (RRDE) methods. The RDE and RRDE results of O2 reduction reveal that GC/MAQ electrodes show rather similar electrocatalytic behaviour towards the ORR yielding hydrogen peroxide as the final product.