Lidia Adamczyk

Effective Charge Transport in Poly(3,4-ethylenedioxythiophene) Based Hybrid Films Containing Polyoxometallate Redox Centers

Electrodeposition and electrochemical charging of hybrid organic/inorganic films composed of the poly(3,4-ethylenedioxythiophene), PEDOT, conducting polymer matrix, and Keggin type polyoxometallate, phosphododecamolybdate(PMo 1 2 O 3 - 4 0 ) or phosphododecatungstate (PW 1 2 O 3 - 4 0 ), redox centers, are described under conditions of aqueous solutions. The systems are electropolymerized through potential cycling as thin and moderately thick (μm level) films on electrode surfaces. They are capable of fast charge propagation during redox reactions in strong acid medium (0.5 mol dm - 3 H 2 SO 4 ). The high overall physicochemical stability of PEDOT is explored to produce a robust, conductive, matrix for such polynuclear mixed-valence inorganic nanostructures as PMo 1 2 O 3 - 4 0 and PW 1 2 O 3 - 4 0 . The composite (hybrid) materials are stabilized due to the existence of electrostatic attraction between anionic phosphomolybdate or phosphotungstate units and positively charged conducting polymer (oxidized). Charge transport is facilitated by the fact that the reversible and fast redox reactions of polyoxometallate appear in the potential range where PEDOT is conductive. The effective diffusion coefficients are on the level 4 X 10 - 8 cm 2 s - 1 . The whole concept may lead to the fabrication of composite (hybrid) films that are capable of effective accumulation and propagation of charge in redox capacitors.

Protection of Steel Against Corrosion in Aggressive Medium by Surface Modification with Multilayer Polyaniline-Based Composite Film

Robust, polyaniline-based, multilayer composite films containing Prussian blue and hexacyanoferrate anions are considered here for the protection of stainless steel (SS) against pitting corrosion in strongly acid media. Polyaniline serves as a stable host matrix for large inorganic anions. At the interface formed by a composite film with SS, the interaction of hexacyanoferrate(II,III) - with iron(II,III), and some chromium(III), results in the formation of a thin insoluble metal hexacyanoferrate (mostly Prussian blue) layer. This phenomenon leads to improved passivation of the steel, and it strongly inhibits metal dissolution even in the chloride acid media. Because the metal hexacyanoferrate deposits are electronically conducting, further electropolymerization of dense and adherent composite polyaniline layers with hexacyanoferrate has been readily achieved. Due to the existence of electrostatic repulsion between negatively charged hexacyanoferrate sites and pitting-causing chloride anions, their transport through the composite film and access to the surface of SS are largely blocked.

Corrosion resistance of stainless steel covered by 4-aminobenzoic acid films

AbstractThe protective, anticorrosion properties of 4-aminobenzoic acid (4-ABA) films are evaluated in the paper. The 4-ABA films were electrodeposited on the surface of both X20Cr13 stainless steel and glassy carbon electrodes by galvanostatically and cyclic voltammetry methods. The protective properties of the resulting films on stainless steel were investigated in the aggressive medium of acidified (pH=4) 0.25 mol dm−3 K2SO4 in the absence and with the presence of 0.5 mol dm−3 KCl. Morphology of the 4-ABA films was examined using scanning electron microscopy.

Hydrogen sorption and corrosion properties of La2Ni9CoSn0.2 alloy

Abstract The hydrogenation and corrosion behaviour of La2Ni9 · CoSn0.2 alloy was analysed in respect of its use in Ni–MH batteries. It has been proved that the presence of tin in the alloy causes a decrease in hydrogen equilibrium pressure. In the electrochemical studies several techniques, such as chronopotentiometry, multi-potential steps, linear sweep voltammetry and the potentiokinetic polarization were applied to characterize the electrochemical properties of a La2Ni9CoSn0.2 powder composite electrode. During long cycling, powder particles undergo micro-cracking or other forms of surface development causing a progressive increase in the exchange current density of the H2O/H2 system, but, on the other hand, this increase favours corrosion processes such as the electrode materials oxidation. This is also reflected in the capacity loss values.

Influence of H3PW12O40 on electrochemical properties of LaCo4.8Bi0.2 alloy

The effect of the surface treatment by H3PW12O40 solution on electrochemical properties of the LaCo4.8Bi0.2 alloy was investigated. A significant increase of hydrogen absorption and a distinct increase of exchange current density was obtained for LaCo4.8Bi0.2 alloy activated with tungstophosphoric acid. Potentiokinetic polarization curves show that the anodic currents increase with the amount of absorbing hydrogen.Graphical abstract