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In this work, the corrosion susceptibility of powder coated Al6060 alloys with increasing Cu and Zn content is evaluated in a benchmark test. Although higher Cu and Zn limits would enable the industry to increase the use of end-of-life scrap and thus produce eco-friendlier aluminium profiles, such alloys are often disregarded due to concerns of corrosion, especially filiform corrosion. Our results suggest that this concern is ungrounded as long as typical quality specifications for the pre-treatment and coating process are followed and the alloy composition is kept within the limits of the European norm AW6060. Furthermore, we point out that the variation of the results due to processing at different coating production lines is larger than the difference between alloys of different Cu and Zn contents.

Modification of multi-walled carbon nanotubes with ultra-thin films of oxocyanoruthenium structures resulted in their improved capacitive characteristics, as evident from increased specific capacitances and energy densities determined using diagnostic charging-discharging electrochemical experiments (involving cyclic voltammetry, galvanostatic and AC impedance methods). The largest specific capacitance (123 F g-1) was found when the oxocyanoruthenium modified carbon nanotubes were further covered or linked with conducting polymer, namely poly (3,4-ethylenedioxythiophene) or PEDOT, structures. Among important issues are high stability of both inorganic and organic components, attractive electrostatic interactions between negatively charged oxocyanoruthenate and positively charged PEDOT, fast redox transitions of oxocyanoruthenium and high dynamics of charge propagation in PEDOT species, as well as ability to improve distribution of charge by mul ti-walled carbon nanotubes.

By modification of surfaces of multi-walled carbon nanotubes with ultra-thin monolayer-type films of phosphododecamolybdic acid, H 3 PMo 12 O 40 , an electrode material with improved capacitance properties is produced. It is apparent from three distinct test experiments (based on cyclic voltammetry, galavanostatic charging–discharging and AC impedance) that capacitors utilizing H 3 PMo 12 O 40 -modified carbon nanotubes are characterized by specific capacitances and energy densities on the levels of 40 F g −1 and 1.3 Wh kg −1 , whereas the respective values for the systems built from bare carbon nanotubes are lower, 22 F g −1 and 0.7 Wh kg −1 . It is reasonable to expect that fast and reversible multi-electron transfers of the Keggin-type H 3 PMo 12 O 40 account for the pseudocapacitance effect and significantly contribute to the observed overall capacitance.

Combination of multi-walled carbon nanotubes, cobalt porphyrin, and peroxidase (horseradish, cabbage) enzyme in the film (deposited onto glassy carbon electrode substrate) produces a bio-electrocatalytic system capable of effective reduction of oxygen in such neutral media as 0.1 mol dm −3 KCl and 0.1 mol dm −3 KCl + 0.01 citrate buffer (pH 6). Carbon nanotubes have been modified with ultra-thin layers of 4-(pyrrole-1-yl) benzoic acid, or phosphododecamolybdate, to form stable colloidal suspensions of carbon nanostructures. The resulting inks have been utilized during sequential deposition of components. Co-existence of cobalt porphyrin, peroxidase enzyme together with dispersed carbon nanotubes leads to synergistic effect that is evident from some positive shift of the oxygen reduction voltammetric potentials (more than 50 mV in citrate buffer) and significant (ca. twice) increase of voltammetric currents (relative to those of the enzyme-free system). The multi-component bio-electrocatalytic film has also exhibited relatively higher activity towards reduction of hydrogen peroxide. It is reasonable to expect that the reduction of oxygen is initiated at cobalt porphyrin redox centers, and the undesirable hydrogen peroxide intermediate is further reduced at the horseradish or cabbage peroxidase enzymatic sites. An important function of carbon nanotubes is to improve transport of electrons within the bio-electrocatalytic multi-component film.

WO3-modified carbon-supported bi-component ruthenium–selenium, RuSex (Ru, 20; Se, 1 wt%), nanoparticles were dispersed in the form of Nafion-containing inks on glassy carbon electrodes to produce electrocatalytic interfaces reactive towards electroreduction of dioxygen in acid medium (0.5 mol dm−3 H2SO4). It was apparent from the rotating disk voltammetric experiments that the reduction of oxygen proceeded at WO3-modified electrocatalyst at more than 100 mV more positive potential when compared to bare (WO3-free) RuSex system (that had been prepared under analogous conditions and deposited at the same loading of 156 μg cm−2). The ring-disk rotating voltammetric measurements show that, while the production of hydrogen peroxide intermediate was significantly lower, the kinetic parameter (heterogeneous rate constant) for the oxygen reduction was higher for WO3-modified RuSex (relative to bare RuSex). Comparison was also made to highly-efficient Vulcan-supported Pt or Pt/Co nanoparticles: while the half-wave potential for the oxygen reduction at WO3-modified carbon-supported RuSex was still more negative relative to the potentials characteristic of Pt-based electrocatalysts, the oxygen reduction rotating disk voltammetric current densities (measured at 1600 rpm) were almost identical.

Surfaces of bulk platinum and unsupported (Vulcan-free) Pt nanoparticles, that are modified and stabilized with such Keggin type heteropolyacids of molybdenum and tungsten as H3PMo12O40 and H3PW12O40, have been characterized using cyclic voltammetry, FTIR (by reflectance), as well as transmission and scanning electron microscopies. The presence of the polyoxometallate monolayer on platinum results in the partial suppression of the interfacial formation of PtOH/PtO oxides. Both molybdates and tungstates seem to interact with Pt surface via their corner oxygen atoms. The existence of spacious, largely hydrated, polyoxometallate monolayers on platinum does not block access of reactant (oxygen) to the catalytic Pt sites. The electrocatalytic properties of H3PMo12O40 and H3PW12O40 modified Pt nanoparticles towards reduction of oxygen in acid medium have been examined and compared using rotating ring–disk voltammetry. Reactivity of Pt-free H3PMo12O40 and H3PW12O40 with respect to reduction of hydrogen peroxide has also been considered. Our results clearly show that modification of Pt nanoparticles with PW12 (but not with PMo12) results in the enhancement of the electrocatalytic reduction of oxygen. © 2007 Elsevier Ltd. All rights reserved.

Nafion stabilized inks of Vulcan XC-72 supported platinum (20 wt.%) nanoparticles (Pt/XC-72) were utilized to produce electrocatalytic films on glassy carbon. The catalysts were modified (activated) with phosphododecatungstic acid H 3 PW 12 O 40 (PW 12 ). Comparison was made to bare (PW 12 -free) electrocatalytic films. Electroreduction of dioxygen was studied at 25 °C in 0.5 mol dm −3 H 2 SO 4 electrolyte using rotating disk voltammetry. For the same loading of platinum (≈95 μg cm −2 ) and for the approximately identical distribution of the catalyst, the reduction of oxygen at a glassy carbon electrode modified with the ink containing PW 12 proceeded at ca. 30–60 mV more positive potential (depending on the PW 12 content), and the system was characterized by a higher kinetic parameter (rate of heterogeneous electron transfer), when compared to the PW 12 -free electrocatalyst. Gas diffusion electrodes with Pt/XC-72 supported on carbon paper (Pt loading 1 mg cm −2 ) were also tested. Under the same experimental conditions, while the exchange current density and the total resistance contribution to polarization components, computed from the galvanostatic polarization curves were found to be clearly higher and lower, respectively, for the ink modified with PW 12 relative to the unmodified system. The results demonstrate that addition of heteropolytungstatic acid (together with Nafion) enhances the electrocatalytic activity of platinum towards reduction of oxygen.

Introduction of carbon-supported RuSex nanoparticles or cobalt protoporphyrin into ultra-thin WO3 matrices results in the enhancement of their electroctalytic properties towards electroreduction of dioxygen in acidic medium (0.5 mol dm-3 H2SO4). The enhancement effects are evidenced from the positive shifts of the O2 reduction potentials (ca 150 mV and 200mV, respectively). An important issue is that the mixed-valent tungsten (VI, V) oxide support is characterized by good electronic and protonic conductivities. Further, not only RuSex and/or cobalt protoporphyrin are catalytic but also the tungsten oxide matrix is reactive: it provides protons and is capable of promoting the reduction of hydrogen peroxide intermediate.

Platinum nanoparticles of ca. 8 nm diameter (that had been first deposited on glassy carbon) were subsequently modified with ultra-thin films of polyoxometallates through their spontaneous adsorption on solid (platinum and carbon) surfaces. The following polyoxometallates (Keggin type heteropolyacids), H3SiW12O40, H3SiMo12O40, H3PW12O40 and H3PMo12O40, were considered as potential activating agents. Rotating disk voltammetry was used to probe the electroreduction of dioxygen in 0.5 mol dm−3 H2SO4 at 25 °C. For the same loading and the approximately identical distribution of platinum nanoparticles on glassy carbon, the statistically higher (in comparison to bare Pt) electrocatalytic currents for the oxygen reduction were observed upon introduction of monolayers of heteropolyanions. Out of polyoxometallates considered, the system modified with heteropolytungstate (H3PW12O40) seemed to be the most effective in electrocatalysis. Although the possibility of structural changes cannot be excluded, the synergistic effect originated presumably from the bifunctional activity of the electrocatalyst. While Pt retained its usual reactivity towards the oxygen reduction, H3PW12O40 could act as both effective mediator (e.g. for the reduction of the hydrogen peroxide intermediate) and the source of mobile protons at the electrocatalytic interface.

The modification of Pt nanoparticles of ca. 8 nm diameter by adsorbing monolayers of phosphododecatungstic acid (H3PW12O40) on their surfaces tends to activate them towards efficient electrocatalytic reduction of oxygen in acid medium. The modification steps were be performed either before or after introduction of catalytic nanoparticles onto the glassy carbon substrates. Formation of a stable colloidal suspension of phosphotungstate protected Pt-nanoparticles as a source of activated catalytic centers was required in the first case; whereas, in the second case, bare Pt nanoparticles had been deposited on glassy carbon before they were subsequently modified with ultra-thin films of H3PW12O40. Rotating disk voltammetry was used to probe the electroreduction of dioxygen in 0.5 mol dm-3 H2SO4. In addition to the usual reactivity towards the oxygen reduction, H3PW12O40 could act as both effective mediator (e.g. for the reduction of the hydrogen peroxide intermediate) and the source of mobile protons at the interface.

We explore oxidative electrocatalytic properties of a system consisting of bimetallic Pt/Ru nanoparticles dispersed over a nanotubular self-organized TiO2 matrix. The nanotubular TiO2 layers consist of individual tubes of 100 nm diameter, 500 nm length and 15 nm wall thickness. This nanotubular TiO2 support provides a high surface area and it significantly enhances the electrocatalytic activity of Pt/Ru for methanol oxidation (relative to the performance of Pt/Ru at the same loading but immobilized on a conventional compact TiO2 support). Annealed to anatase, the TiO2 nanotubular support exhibits even higher enhancement effect during electrooxidation of methanol than when used in the “as-formed” amorphous structure. The overall electrocatalytic activity of the system can be further increased by illumination with UV-light (wavelength 325 nm). Keywords: Titanium dioxide, Nanotubes, Bimetallic Pt/Ru nanoparticles, Electrocatalysis, Methanol oxidation

Using the layer-by-layer technique, carbon submicroparticles, that have been modified and stabilized with monolayers of Keggin-type phosphododecamolybdate (PMo12O 40 3− ), can be dispersed in multilayer films of organic polymers, poly(3,4-ethylenedioxythiophene), i.e., PEDOT, or poly(diallyldimethylammonium) chloride, i.e., PDDA, deposited on glassy carbon or indium-tin oxide conductive glass electrodes. The approach involves alternate treatments in the colloidal suspension of PMo12O 40 3− -covered carbon submicroparticles in the solution of monomer, 3,4-ethylenedioxythiophene or in solution of PDDA polymer. Electrostatic attractive interactions between anionic phosphomolybdate-modified carbon submicroparticles and cationic polymer layers permit not only uniform and controlled growth of the hybrid organic–inorganic film but also contribute to its overall stability. The system composed of PMo12O 40 3− -covered carbon submicroparticles dispersed in PEDOT is characterized by fast dynamics of charge transport and has been used to construct symmetric microelectrochemical redox capacitor. The PDDA-based system has occurred to be attractive for electrocatalytic reduction of hydrogen peroxide.

To fabricate electrocatalytic network films containing Pt nanoparticles, the ability of a Keggin-type polyoxometallate, phosphododecatungstate (PW 12 O 40 3- ), to form stable anionic monolayers on solid surfaces is explored. Three-dimensional assemblies on electrode (glassy carbon or platinum) surfaces are grown using the layer-by-layer method involving repeated alternate treatments in the solution of PW 12 O 40 3- (or in the colloidal suspension of polyoxometallate-protected Pt-nanoparticles) and in the solution of monomer (e.g., anilinium) cations. In the resulting structured (organic-inorganic) films, the layers of negatively charged polyoxometallate, or polyoxometallate-protected (stabilized) Pt-nanoparticles, interact electrostatically with the ultra-thin layers of such a positively charged conducting polymer as polyaniline. Consequently, physicochemical properties of organic conducting polymers, and reactivities of inorganic polyoxometallate and/or noble metal particles can be combined. The modification of Pt nanoparticles by adsorbing monolayers of phosphododecatungstate tends to activate them towards efficient electrocatalytic reduction of oxygen in acid medium.

The tetragonal single crystal, H3PMo12O40⋅29H2O, is considered here as a model system to describe multielectron redox reactions of Keggin type phosphododecamolybdate. Electrochemical experiments have been performed in solid-state, i.e. in the absence of contact with liquid electrolyte phase, and they have utilized a gold wire ultramicrodisk (diameter: 10 μm) working electrode, a silver disk quasireference electrode, and a glassy carbon counter electrode within all solid cell. The results of voltammetric measurements are explained and verified against the simulated data. The reversible redox reactions of phosphododecamolybdic acid (H3PMo12O40⋅29H2O) single crystal, that appear at most positive potentials, can be understood in terms of two overlapping one-electron redox processes (separated by only ≈50 mV), rather than a single two-electron redox transition, followed by another one-electron process. Comparison is made to the conventional electrochemical behavior of phosphododecamolybdate in solution (0.5 mol dm−3 H2SO4) as well as to the characteristic of its adsorbate on the electrode surface. The following parameters have been determined from the combination of potential step experiments performed in two limiting (radial and linear) diffusional regimes: the concentration of heteropolymolybdate redox centers, 1.4 mol dm−3, and the apparent diffusion coefficient for charge propagation, 3.6×10−7 cm2 s−1. The result supports the concept of the kinetic control of charge transport by electron hopping (self-exchange) between mixed-valence (MoVI/MoV) sites.

A novel polymetacrylate-based redox-conducting polymeric gel, into which Keggin-type polyoxometallate, phosphododecatungstic acid (H 3 PW 12 O 40 ), had been incorporated, was electrochemically characterized in the absence of external liquid supporting electrolyte using an ultramicrodisk-working electrode. The phosphotungstate component (15 wt.% of the gel block) was entrapped as the polar organic solvent solution within pores of the polymer matrix. H 3 PW 12 O 40 plays bifunctional role: it provides well-behaved redox centers and serves as strong acid (source of mobile protons). The solid-state voltammetric properties of the system are defined by the reversible one-electron transfers between phosphotungstate redox centers. The following parameters have been determined from the combination of potential step experiments performed in two limiting (radial and linear) diffusional regimes: the concentration of heteropolytungstate redox centers, 6 × 10 −2 mol dm −3 , and the apparent diffusion coefficient, 5 × 10 −7 cm 2 s −1 . The room temperature ionic (protonic) conductivity of the bulk gel was equal to 1.6 × 10 −3 S cm −1 . The charge propagation mechanism was found to be primarily controlled by physical diffusion of heteropolytungstate units within the gel pores rather than by electron hopping (self-exchange) between mixed-valence sites.

The ability of Keggin-type phosphododecamolybdates (PMo12O403-) to undergo chemisorption and to form anionic monolayers on platinum surfaces is explored here to produce stable colloidal solutions of polyoxometalate-protected platinum nanoparticles (size, 5−10 nm, as determined by transmission electron microscopy and scanning tunneling microscopy). By dip-coating in the above solution, the particles can readily be assembled on carbon electrode substrates. The layer-by-layer method, which involves alternate exposures to the solutions of PMo12O403--stabilized Pt nanoparticles and anilinium cations, has been utilized to grow in a controlled manner hybrid network films in which the negatively charged layers of polyoxometalate-protected Pt nanoparticles are linked, or electrostatically attracted, by ultrathin positively charged polyaniline layers. The phosphomolybdate-decorated Pt nanoparticles (immobilized within ultrathin polyaniline film) are attractive for electrocatalysis: they show promising reactivity t...

We describe fabrication of microdimensional polyanilne films in a controlled manner by voltammetric potential cycling or controlled potential electrolysis on platinum microdisk electrodes. The film grows in a form of hemispherical microdeposits, and its size largely exceeds the size of a Pt microdisk. Consequently, the film covers both the Pt substrate as well as the surrounding glass seal. Since the adhering polyaniline layer is conducting, the latter situation may lead to an increase in the effective electrode surface area. The lateral growth of polyaniline films outside the microdisk has also been demonstrated by performing diagnostic voltammetric experiments with use of a double microdisk set-up in which independent polarization of each disk is feasible. Microelectrode-based chronocoulometry, that involves an uncomplicated well-defined reduction potential step starting from the emeraldine (conducting) form and ending at leucoemeraldine (nonconducting) form, yields (upon application of a sufficiently short pulse) a well-defined linear response of charge versus square root of time that is consistent with the linear effective diffusion as the predominant charge propagation mechanism. When describing the system kinetics in terms of the effective (apparent) diffusion coefficient, we expect this parameter to be on the level of 10−8 cm2 s−1 or lower. The relative changes in dynamics of charge transport are discussed with respect to the polyaniline film loading, the size of microdisk electrode, expansion of the active electrode area, and the choice of electrolyte (strong acid) anion. The results are consistent with the view that when Pt microelectrode is modified with PANI deposit exceeding the size of the microdisk substrate, it behaves in a way as if its surface area is effectively much larger than the geometric area of Pt microdisk.

We propose a novel composite organic-inorganic coating in the form of a redox polymer film for protection of stainless steel against general corrosion in strong acid medium (2 M H2SO4). We utilize an anion exchange polymer, protonated poly(4-vinylpyridine), into which hexacyanoferrate anions have been introduced. Owing to the presence of Fe(CN)6 3−/4− at the interface formed by the film and the steel, a sparingly soluble metal hexacyanoferrate (mostly Prussian blue, PB) is formed as an overcoating on the steel’s surface, presumably on the passive (metal oxide) layer. The redox polymer film on the steel seems to act as a composite three-dimensional bilayer-type coating in which hexacyanoferrate(III,II) anions (that are capable of effective charge storage) exist in the outer portions of the film, whereas the inner PB layer improves the system’s overall adherence and stability. By analogy to a conducting polymer (e.g. polyaniline, polypyrrole), introduction of the redox polymer composite film leads to stabilization of the steel substrate’s potential within the passive range.

Integration into a conducting polymer matrix to form a hybrid material is an effective way to harness the electrochemical activity of nanosized oxide clusters. By anchoring them into polyaniline, the reversible redox chemistry of the otherwise soluble polyoxometalate clusters can be combined with that of the conducting polymer and be put to work in energy storage applications. We present here preliminary results that show how the resulting hybrid polymer displays the combined activity of its organic and inorganic components to store and release charge in a solid state electrochemical capacitor device., Partial financial support from the Ministry of Science and Technology (Spain) (Grants MAT2001-1709-C04-01 and MAT2002-04529-C03), and from the Domingo Martínez Foundation, as well as fellowships from the European Marie Curie Program (to M.C.), from the ministry of Education (Spain) (to J.A.A.) and from CONACYT (Mexico) (to K.C.G.) are gratefully acknowledged. P.J.K. and M.C. appreciate partial support from State Committee for Scientific Research (KBN), Poland (Grant 7 T09A 03120).

The ability of a polyoxometallate (dodecamolybdophosphate) to form negatively charged monolayers on solid electrode surfaces is explored here to perform immobilization of monomeric (anilinium) units followed by electropolymerization within the monolayer. Consequently, hybrid films containing ultrathin conducting polymer (polyaniline) layers can be formed. By repeated and alternate treatments in solutions of dodecamolybdophosphate anions and anilinium cations, the amount of the material can be increased systematically in a controlled fashion leading to stable three-dimensional multilayer hybrid assemblies. The fact, that formal potentials of the dodecamolybdophosphate redox processes appear in the potential range where polyaniline is conductive, allows the system to operate reversibly and reproducibly in acid electrolyte. Keywords: Phosphomolybdate, Self-assembled monolayer, Nanostructured polyaniline, Ultrathin composite films, Organized multilayers

We propose a composite bifunctional electrocatalytic film that contains platinum microparticles and oxocyanoruthenium microstructures dispersed in the reactive matrix of non-stochiometric tungsten(VI,V) oxides. Polynuclear oxocyanoruthenium can be viewed as a ruthenium analogue of Prussian blue or, more precisely, ruthenium(II,III,IV) hexacyanoruthenate(II,III), that features ruthenium oxo species within the cyanide bridged network. The composite film was fabricated by sequential electrodeposition starting from the preparation of tungsten oxide film into which oxocyanoruthenium and metallic platinum (from chloroplatinate) centers were introduced. To evaluate the reactivity of such a hybrid system toward the oxidation of methanol at fairly low potentials (0.1–0.3 V vs. SCE), cyclic voltammetric and chronoamperometric measurements have been performed at 22 and 60 °C. With approximately the same platinum loading and under analogous conditions, the composite film shows higher catalytic activity than a simple platinized tungsten oxide. It is possible that ruthenium hydroxo species generated within polynuclear oxocyanoruthenium microstructures exhibit an activating effect on neighboring dispersed platinum microparticles. An alternative explanation may involve the possibility of different morphologies of the catalytic films in the presence and absence of oxocyanoruthenium species. At higher potentials, ruthenium(IV)-oxo centers participate directly in the oxidation of methanol. The protonically/electronically conducting and physicochemically stable tungsten oxide/hydrogen bronze matrix is expected to support the activity of platinum and ruthenium centers.

We propose novel composite (hybrid) organic/inorganic systems that can be fabricated as thin and moderately thick (μm level) films on electrode surfaces. During electrodeposition by potential cycling alternate layers of polyanilne and metal hexacyanoferrate are produced. Polyaniline can serve as a robust, conductive, matrix for such polynuclear mixed-valence inorganic redox centers as nickel(II)hexacyanoferrate(III,II). Due to the existence of electrostatic attraction between the negatively charged metal hexacyanoferrate and the positively charge polyaniline (partially oxidized), the composite material cannot be considered as a simple mixture of nickel hexacyanoferrate and the conducting polymer. It comes from atomic force microscopic studies that the morphology of the composite film is granular, but its structure is fairly dense. The fact, that the formal potential of nickel hexacyanoferrate redox process lies in the potential range where polyaniline is conductive, allows the system to operate reversibly and reproducibly in acid electrolytes containing potassium cations. The whole concept may lead to the fabrication of composite (hybrid) films that are capable of effective accumulation of charge and show high current densities at electrochemical interfaces.

The ability of a Keggin-type polyoxometallate, phosphododecamolybdate (PMo12O403−), to form stable anionic monolayers on carbon nanoparticles and multi-wall nanotubes is explored here to produce stable colloidal solutions of polyoxometallate covered carbon nanostructures and to disperse them within conducting polymer, poly(3,4-ethylenedioxythiophene), i.e. PEDOT, or polyaniline multilayer films. By repeated alternate treatments in the colloidal suspension of PMo12O403−-protected carbon nanoparticles or nanotubes, and in the acid solution of a monomer (3,4-ethylenedioxythiophene or aniline), the amount of the material can be increased systematically (layer-by-layer) to form stable three-dimensional organized arrangements (networks) of interconnected organic and inorganic layers on electrode (e.g. glassy carbon) surfaces. In hybrid films, the negatively charged polyoxometallate-covered carbon nanostructures interact electrostatically with positively charged conducting polymer ultra-thin layers. Consequently, the attractive electrochemical charging properties of conducting polymers, reversible redox behavior of polyoxometallate, as well as the mechanical and electrical properties of carbon nanoparticles or nanotubes can be combined. The films are characterized by fast dynamics of charge transport, and they are of potential importance to electrocatalysis and charge storage in redox capacitors.

The formation of a rigid bilayer structure from two metal hexacyanoferrates: Prussian blue (PB) and nickel hexacyanoferrate (NiHCNFe), as inner and outer films, respectively, has been demonstrated. To avoid intermingling of the granular cyanometallate microstructures, namely of the outer film (NiHCNFe) into the inner film (PB), the morphology of outer film material was changed by forming a polymeric hybrid (composite) of NiHCNFe with poly(N-methylpyrrole). The outer NiHCNFe film is physically separated from the electrode surface, and it undergoes redox reactions at potentials characteristic of the inner PB film. This arrangement leads to the reversible charge state trapping and bistable switching during voltammetric potential cycling. Under solid-state voltammetric conditions in the absence of contact with the liquid electrolyte phase, when the bilayer structure of PB and the oxidized NiHCNFe was formed between two sandwich-forming carbon electrodes, unidirectional rectifying current flow has been observed.

A novel electroanalytical approach is proposed here, and it is demonstrated with the direct and simultaneous determination of two unknowns: the concentration of redox sites and the apparent diffusion coefficient for charge propagation in a single crystal of dodecatungstophosphoric acid. This Keggin-type polyoxometalate serves as a model bulk redox conducting inorganic material for solid-state voltammetry. The system has been investigated using an ultramicrodisk working electrode in the absence of external liquid supporting electrolyte. The analytical method requires numerical solution of the combination of two equations in which the first one describes current (or charge) in a well-defined (either spherical or linear) diffusional regime and the second general equation describes chronoamperometric (or normal pulse voltammetric current) under mixed (linear-spherical) conditions. The iterative approach is based on successive approximations through calculation and minimizing the least-squares error function. The method is fairly universal, and in principle, it can be extended to the investigation of other bulk systems including sol-gel processed materials, redox melts, and solutions on condition that they are electroactive and well behaved, they contain redox centers at sufficiently high level, and a number of electrons for the redox reaction considered is known.

We develop a concept of fabrication of the multilayer network films on electrodes by exploring the ability of a Keggin-type polyoxometallate, phosphododecamolybdate (PMo 12 O 40 3− ), to form stable anionic monolayers (templates) on carbon and metals including platinum. By repeated alternate treatments in the solution of PMo 12 O 40 3− (or in the colloidal suspension of polyoxometallate-protected Pt-nanoparticles) and in the solution of monomer (e.g. anilinium) cations, the amount of the material can be increased systematically (layer-by-layer) to form stable three-dimensional assemblies on electrode (e.g. glassy carbon) surfaces. In the resulting hybrid (organic–inorganic) films, the layers of negatively charged polyoxometallate, or polyoxometallate-protected (stabilized) Pt-nanoparticles, are linked or electrostatically attracted by ultra-thin layers of such positively charged conducting polymers as polyaniline (PANI), polypyrrole (PPy) or poly(3,4-ethylenedioxythiophene), PEDOT. Consequently, the attractive physicochemical properties of polymers and reactivity of polyoxometallate or noble metal particles are combined. The films are functionalized and show electrocatalytic properties towards reduction of nitrite, bromate, hydrogen peroxide or oxygen. They are of importance to the chemical and biochemical sensing as well as to the biochemical and medical applications.

Hybrid organic/inorganic films, composed of polyaniline (PANI) matrix and Prussian blue-like nickel hexacyanoferrate redox centers, showed reversible electrochromic behavior in acidic potassium salt electrolytes. The system's coloration properties were assessed from various spectroelectrochemical measurements including voltabsorptometry that involved monitoring of the time-derivative signal of absorbance at 700 and 410 nm as a function of linearly scanned potential. Gold-covered foil was used as a conductive, optically transparent, substrate onto which the composite film was electrodeposited by potential cycling in the mixture for modification consisting of aniline monomer, Ni2+, Fe(CN)63− and electrolyte containing K+ and H+ ions. An important feature of hybrid (composite) material was that its electrochromic properties were dominated by color changes occurring in the PANI component. Coloration originating from nickel hexacyanoferrate barely affected the system's electrochromic characteristics. But the cyanometallate redox centers distributed in the PANI matrix behaved reversibly as expected for a system capable of fast charge transport.

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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.

Electro-oxidative polymerization of aniline is facilitated by modification of electrode surfaces with an inorganic polyoxometalate, namely with self-assembled monolayers of dodecamolybdophosphate, PMo 12 O 3- 40 and dodecatungstophosphate PW 12 O 3- 40 . Introduction of a protonated and therefore positively charged 1,12 diaminododecane [NH 2 -(CH 2 ) 12 -NH 2 ] adlayer can invert the interfacial charge and significantly inhibits the access of anilinium monomers. Consequently, the deposition of polyaniline with spatial selectivity is feasible, and preferential growth of the polymer on electrode surfaces modified with polyoxometalate has been observed. Microcontact printed patterns of the polyoxometalate or of 1,12 diaminododecane on top of a full polyoxometalate monolayer allows the electropolymerization of aniline to be triggered or inhibited locally.

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.

Hensikten med denne oppgaven var å se på hvordan ulik temperatur og volum av elektrolyttløsning påvirket resultatet ved testing av korngrensekorrosjon i resirkulert aluminium, i henhold til ISO 11846 Metode B. Det ble også undersøkt hvordan legeringselementer, særlig kobber og sink, påvirket korngrensekorrosjon. Metode B fra ISO 11846 (IGC standard) ble gjennomført for 6 ulike 6005-legeringer med ulikt innhold av elementene Cu, Mg, Si, Zn, Fe og Mn. Prøvene var ekstruderte modell-legeringer som har blitt vannavkjølt og herdet til T6 tilstand. Prøvene ble neddykket i elektrolytt i 24 timer. Det ble utført tre paralleller for å variere temperatur og volum av elektrolyttløsning. Tverrsnittet på to ulike steder i prøven ble undersøkt i lysmikroskop for å se på korrosjonsdybden. Prøvene ble også veid før og etter for å beregne massetap. Rangering av legeringenes motstand mot korngrensekorrosjon skulle hovedsaklig baseres på korrosjonsdybde. Resultatene indikerte at økt volum av elektrolytt ga dypere korrosjonsangrep for legeringene med lavt sinkinnhold. Økning av temperatur ga dypere korrosjonsangrep for legeringene med lavt kobberinnhold, men grunnere angrep for legeringene med høyt kobberinnhold. Økt temperatur ga jevne angrep over hele overflaten, mens ved romtemperatur var angrepene lokale og spredte. De ulike legeringene ble rangert forskjellig i hver parallell, og det kan tyde på at det er mulig å tilpasse testparameterne for å oppnå ønsket resultat av testen. Det er tydelig at økt kobberinnhold gir økt korngrensekorrosjon, mens innholdet av sink har gitt tvetydige resultater. Ytterligere testing kreves for å kunne konstatere effekten av sink. The objective of this thesis was to study whether the change of temperature and volume of the electrolyte solution would affect the results when testing grain boundary corrosion in recycled aluminium, using ISO 11846 Method B. It was also investigated how alloying elements, particularly copper and zinc, affected grain boundary corrosion. Method B from ISO 11846 (IGC standard) was carried out for 6 different 6005-alloys containing varying amounts of Cu, Mg, Si, Zn, Fe and Mn. The samples were water cooled after extrusion and aged to T6 condition. In accordance to Method B, the test specimens were fully submerged in an electrolyte for 24 h. Two test parameters, temperature and volume of electrolyte solution, was varied to see how it affected the results. Two different cross sections from each specimen was studied in an inverted microscope to measure the depth of the corrosion attack. Furthermore, each sample was weighed before and after the experiment to calculate the mass loss. Determination of the alloys' resistance to intergranular corrosion was mainly based on the corrosion depth. The results indicated that an increase in volume of the electrolyte gave a deeper corrosion attack for the alloys with low zink content. The increase in temperature gave a deeper corrosion attack only for the alloys with low copper content, and a more shallow attack for those with a higher copper content. The increase in temperature also gave a more even attack across the surface of the specimens, whereas for room temperature, the attacks were local and irregular. The different alloys were ranked differently in each parallel. This can imply that the test parameters can be adjusted to give a preferable result. It was also clear that the increase in copper content gave an increase in intergranular corriosion, whilst the zink content showed ambiguous results. Further testing is necessary in order to ascertain the influence of zink.