M. Tölgyesi

Electrochemical reactions of cytochrome c on electrodes modified by fullerene films

Abstract C60 fullerene film modified electrodes were investigated for the electrochemical reactions of cytochrome c. It was established, that depending on the oxidation state of the fullerene films, the electrochemistry of the protein varied. The best, stablest redox reaction could be measured on partially reduced film. The response of cytochrome c was quite independent of the underlying substrate (gold or glassy carbon), indicating that the fullerene film acted as a promoter. Molecular sieve character and the possible effect of negative charges or polar groups on the surface of the films were suggested to be the reason of enhanced stability of the electrochemical response compared to bare electrodes.

Electrochemistry on partially reduced fullerene films

Abstract Electrochemical studies on solution cast fullerene (C60, C70) films were carried out in aqueous solutions. It was observed that a special pretreatment of films in quinhydrone solution could provide suitable conditions to investigate the electrochemical behavior of fullerene films exclusively. It was found that fullerene films can conduct electrons to the solution phase in their partially reduced forms. They behave as diodes with pronounced current rectifying character. Results on these partially reduced layers also support conclusions on the bulk reduction of the fullerene films in aqueous media.

Photoelectrochemical behaviour of C60 films in various oxidation states

Abstract The photoelectrochemical behaviour of C 60 films, deposited on gold and glassy carbon surfaces, was studied in various oxidation states, and with various compounds in the solution phase. It was established that neutral C 60 films behave as porous intrinsic semiconductors, and they can be converted to porous n-type semiconductors upon reduction in the presence of Li + , or Na + . If the reduction was carried out in K + -, Rb + -, or Cs + -containing solutions, the reduced films were pure conductors. Depending on the size of the electroactive species in the electrolyte, both photo-oxidation and photoreduction could be observed on the semiconducting reduced films. The spectral dependence of the photocurrents was also determined, and some basic parameters of the films were established.

Redox anion doped polypyrolle films; electrochemical behaviour of polypyrrole prepared in Fe(CN)6 solution

Polypyrrole films were formed with hexacyano-ferrate (HCF) anions as exclusive dopants. It was observed that a portion of the built-in HCF displayed reversible electro-chemistry, but the majority of the doping anions are non-electroactive, while they are inside the polymers. Calculations showed that one excess positive charge on the polymer backbone was compensated by one HCF ion, thus, the entrapment of these multivalent anions was accompanied by the inclusion of a large amount of cations as well. These films were sensitive for the size of the cations present in the solution.

Manganese-doped fullerene film electrodes

Abstract Manganese-doped C 60 fullerene films were produced on glassy carbon substrates by electrochemical reduction in aqueous solutions. It was established that manganese ions can be inserted into the fullerene lattice during the fullerene reduction initiated by potassium or sodium ions. The final reduced fullerene was mixed doped, containing either potassium and manganese, or sodium and manganese fulleride. The formation of manganese fulleride was explained by a mechanism involving ion exchange.

On the mixed doping of fullerene films

Abstract Mixed doping of C 60 fullerene films on gold substrates was carried out by electrochemical reduction in aqueous solutions, producing a variety of electrodes. It was established that the ratio of the built-in dopants (cations) can be controlled on the solution side by adjusting the ratio of the concentrations of the different cations. Ion-exchange was proposed as the determining step. From the experiments of mixed doping, conclusions on the existence of transient species, and on the mechanism of the reduction of fullerene films, were also drawn.

Electrochemistry of C70 fullerene films in aqueous solutions

Abstract The electrochemical behavior of C 70 fullerene films on gold and glassy carbon substrates was studied in aqueous solutions. The neutral C 70 film behaved as an intrinsic semiconductor electrode, and it could be transformed to a conductor by electrochemical reduction. We observed that C 70 could be reduced in the presence of various cations, and the reduction process shifted parallel with the hydration Gibbs energy of the cations. In each case the reduction consumed about three electrons per C 70 molecule. The potential of the reduction changed with the activity of the cations, indicating the formation of some ion-exchanging transient species. The C 70 fullerene electrodes had good stability at ambient conditions.