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A membrane-free biofuel cell (BFC) is reported based on enzymes wired to graphite electrodes by means of Os-complex modified redox polymers. For the anode cellobiose dehydrogenase (CDH) is used as a biocatalyst whereas for the cathode a laccase was applied. This laccase is a high-potential laccase and hence able to reduce O-2 to H2O at a formal potential higher than +500 mV versus Ag/AgCl. In order to establish efficient electrochemical contact between the enzymes and graphite electrodes electrodeposition polymers containing Os-complex with specifically designed monomer compositions and formal potentials of the coordinatively bound Os-complex were synthesised and used to wire the enzymes to the electrodes. The newly designed CDH/Os-redox polymer anode was characterised at different pH values and optimised with respect to the nature of the polymer and the enzyme-to-polymer ratio. The resulting BFC was evaluated running on beta-lactose as a fuel and air/O-2 as an oxidising agent. The power output, the maximum current density and the electromotor force (E-emf) were found to be affected by the pH value, resulting in a maximum power output of 1.9 mu W cm(-2) reached at pH 4.3, a maximum current density of about 13 mu A cm(-2) at pH 3.5, and the highest E-emf approaching 600 mV at pH 4.0.

The ability of such a common redox mediator as 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) to undergo sorption on carbon surfaces is explored here to convert multiwalled carbon nanotubes (CNTs) into a stable colloidal solution of ABTS-modified carbon nanostructures, the diameters of which are approximately 10 nm (as determined by transmission electron microscopy). Subsequently, inks composed of fungal laccase (Cerrena unicolor) mixed with the dispersion of ABTS-modified CNTs and stabilized with Nafion, were deposited on glassy carbon and successfully employed to the reduction of oxygen in McIlvain buffer at pH 5.2. For comparison, the systems utilizing only ABTS-free CNTs and laccase as well as ABTS-modified CNTs did not show appreciable activity toward the oxygen reduction. The three-dimensionally distributed ABTS-modified CNTs are expected to improve the film's overall conductivity and to facilitate electrical connection between the electrode and the enzyme. The network film of ABTS-modified CNTs is rigid, and it is characterized by charge propagation capabilities comparable to the conventional redox polymers. The whole concept of utilization of CNTs modified with ultrathin films of redox mediators in the preparation of efficient bioelectrocatalytic films seems to be of general importance to electroanalytical chemistry and to the development of biosensors.

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.

Combination of polyoxometallate-modified multi-walled carbon nanotubes, cobalt porphyrin, and peroxidase (horseradish, cabbage) enzyme within the film (deposited on glassy carbon) produces a bio-electrocatalytic system capable of effective reduction of oxygen in neutral media such as 0.1 mol dm-3 KCl and 0.1 mol dm-3 KCl + 0.01 citrate buffer (pH=6). An important function of carbon nanotubes is to improve transport of electrons within the film. Co-deposition of the peroxidase enzyme together with the cobalt porphyrin catalytic centers leads to bifunctional synergistic effect that is evident from sizeable positive shift of the oxygen reduction potentials and significant increase of voltammetric currents. The bio- electrocatalytic system also exhibits relatively much higher reductive activity towards hydrogen peroxide. It is reasonable to expect that the reduction of oxygen is initiated at cobalt porphyrin redox centers, and the undesirable hydro gen peroxide intermediate is further reduced at the horseradish or cabbage peroxidase enzymatic sites.

Optimisation of biocatalytic systems for the electroreduction of molecular O2 in biofuel cell cathodes implies screening of the catalytic activity of enzyme/redoxpolymer assemblies. Os-complex modified electrodeposition polymers are suggested for linking bilirubin oxidase catalysed O2 reduction via an electron hopping sequence along the redox polymer to the electrode. They can be non-manually precipitated on electrode surfaces by electrochemically induced pH modulation. Cyclic voltammetry provides a good estimation of the electrocatalytic activity of a redox polymer/enzyme modified electrode surface. In addition, scanning electrochemical microscopy operating in redox competition mode (RC-SECM) supplies images of the spatial distribution of the biocatalytic activity. Keywords: Bilirubin oxidase, Biofuel cell, Electrodeposition paint, Redox polymers, Oxygen reduction, SECM, RC-SECM, Redox competition

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.

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.

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 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...

Multiwalled carbon nanotubes were entrapped in sol-gel processed hydrophilic silicate thin film on tin-doped indium oxide support. Microscopic images show that the nanotubes form large agglomerates of largely separated nanotubes covered by silicate film. The measurements of capacitive current prove that approximately 10% of them remain electrochemically active. The surface confined cyclic voltammetry indicate adsorption of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) on this material. The oxidation charge estimated after the adsorption saturated shows that this compound is adsorbed on almost all the surface of the immobilised carbon nanotubes. After further modification of the electrode with extracellular laccase from Cerrena unicolor electrocatalytic dioxygen reduction is observed. The immobilised enzyme exhibits catalytic action whereas 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) adsorbed on carbon nanotubes serves as electron mediator between protein and electrode. Bioelectrocatalysis is also observed in the absence of adsorbed mediator but the efficiency of the process is approximately one order of magnitude smaller.

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.

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.

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Fundamental reflectivity spectra of thin polycrystalline and amorphous thin Cd 3 As 2 films are reported. The results for polycrystalline samples can be qualitatively explained in terms of a reflecting surface roughness only. For amorphous films the most probable explanation is provided by variations in the short- and medium- range order.

Fundamental reflectivity spectra of mono and polycrystalline bulk samples of Cd 3 As 2 in the energy range 0.8 – 5.9 eV are measured. The results are compared with existing experimental data and are interpreted on the basis of Lin-Chung model.