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 CO_ad oxidation rate increases with the accumulation of CO_ad until the maximum CO_ad coverage (ca. 0.5 ML i.e., the steady state) is reached; (ii) at fixed CO_ad coverage, the rates for MeOH decomposition to CO_ad and CO _ad 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 CO_ad 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.