Pulsed‐Potential Oxidation of Methanol: I . Smooth Platinum Electrode with and without Tin Surface Modification

Abstract

During the electrooxidation of methanol on platinum, an adsorbate poison forms which results in the rapid decay of the initially high current. The poison may be oxidatively removed to regenerate an active Pt surface, but only at a high anodic polarization at which a methanol fuel cell may not produce power. In this paper, an alternative strategy to steady‐state (DC) operation is studied as a means of improving the average methanol oxidation rate on a smooth Pt electrode. A periodic, rectangular waveform is potentiostatically applied alternating from a high anodic polarization of duration to a low anodic polarization of duration for a cycle time equal to . The potential is sufficiently anodic to oxidize the poison to form carbon dioxide; during the remainder of the cycle, the polarization is lowered to at which methanol oxidation occurs. A fixed value of was used (1.18 V), and the effects of , , and were studied. In addition, surface modification of the electrode with Sn in conjunction with the periodic control was examined. For both the unmodified and Sn‐modified Pt electrode, the current density exhibited a maximum with frequency at each . The time‐averaged methanol oxidation current density at was three orders‐of‐magnitude above the DC current of 9 μA/cm2 at the same voltage; at , a five orders‐of‐magnitude increase was found above a DC current of 0.03 μA/cm2. From conventional current‐voltage‐time and coulomb measurements, the most likely poison composition is . In the presence of Sn, the time‐averaged methanol oxidation current at was at best approximately a factor of 2 above that obtained in its absence using the same potential waveform.