Abstract
The importance of morphology and electrochemical characteristics of tungsten oxide as a support for the catalytic platinum/ruthenium nanoparticles during electro-oxidation of methanol in acid medium is addressed here. Bimetallic Pt/Ru nanoparticles were immobilized at the same loadings in three different WO3 matrices. Application of high voltages (up to 40V at 1Vs-1) to tungsten foil in H2SO4 solution containing a small amount of NaF (0.15 wt %) resulted in the formation of highly ordered nanoporous WO3. Compact tungsten oxide was produced by application of high voltages to tungsten foil in the absence of NaF. Parallel measurements were done with conventional thin films of microporous tungsten oxide electrodeposited on a glassy carbon substrate from the colloidal Na2WO4 solution in H2SO4. While redox reactions of the structures generated by high voltage anodization were characteristic of poorly hydrated WO3 (that could be reduced partially to substoichiometric oxides, WO3-y), the conventionally electrodeposited microporous structures behaved more like hydrated WO3 (that could be reduced to nonstoichiometric hydrogen bronzes, HxWO3). Contrary to compact structures (that were blocking Pt/Ru reactivity), both ordered nanoporous and electrodeposited microporous WO3 matrices, that were more open and characterized by high surface areas, significantly enhanced the electrocatalytic (chronoamperometric, voltammetric) currents for methanol oxidation. Among important advantages of the system produced by assembling Pt/Ru in nanoporous WO3 are its rigidity, long-term stability, and the ability to oxidize methanol at less positive potentials.