Electrocatalytic oxidation of methanol on Pt modified polyaniline in alkaline medium

A comparative study of the electrocatalytic oxidation of methanol is made in NaOH, Na₂CO₃ and NaHCO₃ on bare Pt (Pt), polyaniline covered Pt (PANI) and Pt modified polyaniline film on Pt (Pt/PANI) using cyclic voltammetry, polarization, ac impedance spectroscopy and chronoamperometric techniques at 25 °C. The cyclic voltammetry and polarization studies show that the potentials at which methanol oxidation commences on different electrodes in each of the alkaline medium examined follow the trend Pt/PANI < Pt < PANI whereas the potentials for initiation of oxidation on each electrode in different alkaline media follow the order NaHCO₃ > Na₂CO₃ > NaOH. The oxidation current is highest and charge transfer resistance lowest for Pt/PANI films compared to Pt in all the media studied. However, for the same Pt loading Pt/PANI films exhibit larger oxidation currents in NaOH followed by Na₂CO₃ and NaHCO₃. The Tafel slope for methanol oxidation on Pt/PANI in NaOH, Na₂CO₃ and NaHCO₃ has a value of about 115 mV decade⁻¹. The chronoamperometric response of the Pt/PANI film at the peak potential for methanol oxidation shows lesser sensitivity to poisoning by CO compared to bare Pt and platinised Pt (Pt/Pt).