Electrocatalytic Oxidation of Methanol by Assemblies of Platinum/Tin Catalyst Particles in a Conducting Polyaniline Matrix

Oxidation of MeOH at electrodes modified with polyaniline and Pt/Sn particles has been studied in aqueous H₂SO₄ electrolyte at 298 K. The Pt/Sn particles have been deposited into the polyaniline by electrochemical deposition from aqueous H₂SO₄ containing Pt(IV) and Sn(IV) from addition of K₂PtCl₆ and SnCl₄·5H₂O, respectively. The activity for MeOH oxidation is higher than that of polyaniline-coated electrodes modified with Pt alone. The highest catalytic activity is observed for Pt/Sn particles that are codeposited from solutions containing 7 mμ Sn(IV) when a 3 mM Pt(IV) solution is used. Characterization of the electrodes by SEM and scanning Auger spectroscopy shows that the code position procedure yields roughly spherical catalyst particles containing both Pt and Sn. Significantly the two metals are found together, as determined by high lateral resolution Auger electron spectroscopy. Samples analyzed by X-ray photoelectron and Auger spectroscopy show variability in the Pt:Sn ratio for samples prepared in the same fashion, but the most active catalysts typically show surface ratios of Pt:Sn between 8:1 and 2:1. For catalyst loading of ~0.5 mg/cm² we find anodic currents of ~5 mA/cm² at +0.3 V vs SCE at 298 K for MeOH oxidation in 0.5 M H₂SO₄ containing 20% (by volume) MeOH. The onset of MeOH oxidation is near 0 V vs SCE.