Margus Marandi

Hydrodynamic Deposition of Carbon Nanotubes onto HOPG: The Reduction of Oxygen on CNT/HOPG Electrodes in Alkaline Solution

The electrochemical reduction of oxygen on highly oriented pyrolytic graphite (HOPG) electrodes coated with multiwalled carbon nanotubes (MWCNTs) was investigated in alkaline media using the rotating disk electrode (RDE) technique. A hydrodynamic method was employed for the deposition of nanotubes onto HOPG. The surface morphology of the MWCNT-modified HOPG electrodes was examined by atomic force microscopy. RDE studies indicate that the MWCNT/HOPG electrodes reveal a remarkable electrocatalytic activity toward O 2 reduction, and the surface morphology of the modified electrodes showed that the distribution of nanotubes on the HOPG surface was rather uniform and no essential agglomeration was evident.

Blocking properties of gold electrodes modified with 4-nitrophenyl and 4-decylphenyl groups

The electrochemical properties of Au electrodes grafted with 4-nitrophenyl and 4-decylphenyl groups have been studied. The electrografting of gold electrode surface with aryl groups was carried out by electroreduction of the corresponding diazonium salts in acetonitrile. The nitrophenyl film growth on gold was examined by atomic force microscopy, electrochemical quartz crystal microbalance and X-ray photoelectron spectroscopy. These measurements showed that a multilayer film of nitrophenyl groups was formed. Cyclic voltammetry was used to study the blocking properties of aryl-modified gold electrodes towards the Fe(CN)63−/4− redox system. The reduction of oxygen was strongly suppressed on these electrodes as evidenced by the rotating disc electrode results.

Study of the Properties of Electrodeposited Polypyrrole Films

Experimental and theoretical methods have been used for characterization of the properties of polypyrrole films. The AFM studies show that the morphology of polypyrrole (PPy) films on polycrystalline gold electrodes at the first stages of synthesis depends on the structure of the metal surface. It was established that mobility of anions depends remarkably on the rate of electrodeposition of the polymer film. If PPy film was deposited at relatively low current density, mobility of ClO-4 anion was not high enough to guarantee electroneutrality during redox cycling and cations take part in this process especially when Li+ cations were replaced by more mobile К+ cations. Semiempirical (AM1 and PM3) quantum-chemical methods were used for theoretical studies. It was established that different size and charge of the anions together with the variation in doping levels give rise to a different optimal conformation of oligopyrrole cations which, in turn, define the resulting polymer to be either all-anti (common linear chains) or all-syn (formation of helical structures) or a combination of the two.

Electrochemical Modification of Gold Electrodes with Azobenzene Derivatives by Diazonium Reduction

An electrochemical study of Au electrodes electrografted with azobenzene (AB), Fast Garnet GBC (GBC) and Fast Black K (FBK) diazonium compounds is presented. Electrochemical quartz crystal microbalance, ellipsometry and atomic force microscopy investigations reveal the formation of multilayer films. The elemental composition of the aryl layers is examined by X-ray photoelectron spectroscopy. The electrochemical measurements reveal a quasi-reversible voltammogram of the Fe(CN)6 (3-/4-) redox couple on bare Au and a sigmoidal shape for the GBC- and FBK-modified Au electrodes, thus demonstrating that electron transfer is blocked due to the surface modification. The electrografted AB layer results in strongest inhibition of the Fe(CN)6 (3-/4-) response compared with other aryl layers. The same tendencies are observed for oxygen reduction; however, the blocking effect is not as strong as in the Fe(CN)6 (3-/4-) redox system. The electrochemical impedance spectroscopy measurements allowed the calculation of low charge-transfer rates to the Fe(CN)6 (3-) probe for the GBC- and FBK-modified Au electrodes in relation to bare Au. From these measurements it can be concluded that the FBK film is less compact or presents more pinholes than the electrografted GBC layer.

Electrochemical properties of gold and glassy carbon electrodes electrografted with an anthraquinone diazonium compound using the rotating disc electrode method

In this paper, gold and glassy carbon (GC) electrodes were electrochemically grafted with anthraquinone (AQ) groups derived from Fast Red AL salt via electrochemical reduction of AQ diazonium cations. For the first time, the electrografting was performed by combining the cyclic voltammetry (CV) or potential step method with the rotating disc electrode (RDE) technique in order to prepare thick films of AQ on Au and GC electrodes. For comparison purposes, a CV or potential step method without the RDE was also used. The attachment of thick AQ films to the Au electrode surface was confirmed by X-ray photoelectron spectroscopy and atomic force microscopy. The highest surface concentration value (ΓAQ) of AQ on the Au and GC electrodes (ca. 2.1 × 10−8 and 1.8 × 10−8 mol cm−2, respectively) was obtained by employing the combination of CV and RDE methods during the electrografting procedure. The oxygen reduction reaction results revealed that the electrochemical behaviour of AQ-modified Au electrodes does not depend on the ΓAQ value similar to the GC electrodes modified with thick AQ films. However, some differences were observed when the blocking effect of thick AQ films on Au and GC electrodes towards the ferri/ferrocyanide redox probe was studied.