The ability of Keggin-type phosphododecamolybdates (PMo 12 O 40 3-) 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 PMo 12 O 40 3--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 toward the electroreduction of oxygen.

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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 O2 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 β‐lactose as a fuel and air/O2 as an oxidising agent. The power output, the maximum current density and the electromotor force (Eemf) were found to be affected by the pH value, resulting in a maximum power output of 1.9 μW cm–2 reached at pH 4.3, a maximum current density of about 13 μA cm–2 at pH 3.5, and the highest Eemf 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.

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