The kinetics of CO pathway in methanol oxidation at Pt electrodes, a quantitative study by ATR-FTIR spectroscopy

Methanol (MeOH) oxidation reaction (MOR) at Pt electrodes under potentiostatic conditions has been investigated by electrochemical in situ FTIR spectroscopy (FTIRS) in attenuated-total-reflection configuration under controlled flow conditions in 0.1 M HClO4 with 2 M MeOH, where the mass transport effects are largely eliminated using a flow cell. Our results reveal that (i) at constant potentials, the methanol dehydrogenation rate decreases while the COad oxidation rate increases with the accumulation of COad until the maximum COad coverage (ca. 0.5 ML i. e., the steady state) is reached; (ii) at fixed COad coverage, the rates for MeOH decomposition to COad and COad oxidation increases with potential from 0.3 to 0.7 V (vs. RHE), with Tafel slopes for MeOH dehydrogenation of ca. 440 +/- 30 mV/dec, which is independent of COad coverage; (iii) the current efficiency of the CO pathway in MOR at 0.6 and 0.7 V is below 20% and it decreases toward higher potentials. The mechanisms as well as the potential induced change in the kinetics of different pathways involved in MOR are briefly discussed.