Specular reflectivity studies of the adsorption and the oxidation of methanol on palladium in an alkaline solution

Adsorption and anodic oxidation of methanol on palladium electrode in 0·5 N NaOH was studied by measuring current—potential (i-E) and reflectivity—potential (R/R₀-E) curves. Presence of methanol retarded the formation of the oxide layer of Pd, giving rise to an anodic shift of the potential. A linear relation was found between the potential retarded and the logarithm of methanol concentration, the slope being about 30 mV/decade. The form of adsorbed entities was discussed based on the slope. The cathodic charge consumed by the reduction of Pd-oxide was smaller in the presence of methanol than in the absence. This was explained by three causes; the less amount of oxide layer formed during the anodic sweep owing to the adsorption of oxidation product of methanol, the reduction of formed oxide layer by a chemical reaction with methanol, and a compensation effect due to the anodic oxidation of methanol during the cathodic sweep. Plottings of the total charge in the anodic region vs — ΔR/R₀ in the absence and the presence of methanol suggested that electro-oxidation of methanol proceeds only at the bare portion of Pd.