Oxidation of methanol at an electrocatalytic film containing platinum and polynuclear oxocyanoruthenium microcenters dispersed within tungsten oxide matrix

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 degreesC. 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. (C) 2001 Elsevier Science B.V. All rights reserved.