In this contribution, we describe a method to estimate the kinetics of the indirect pathway in methanol oxidation reaction (MOR) at Pt electrode by using electrochemical in situ infrared spectroscopy combined with a thin-layer flow cell. Based on a quantitative relationship between the coverage of adsorbed carbon monoxide (COad) and its infrared band intensities determined experimentally, COad coverages during MOR are estimated from the simultaneously recorded time-resolved IR measurements. By assuming that CO ad oxidation goes through Langmuir-Hinshelwood mechanism, its rate constant is estimated in pure supporting electrolyte under otherwise identical condition. Based on the result, the rates of COad formation and COad oxidation during MOR are deduced from the COad coverage-time curve. The methodology is exemplified with MOR on Pt electrode at +0.6 V (versus RHE) in 0.1 M HClO4 with 2 M methanol. It is found that under forced-flow condition: (i) the maximum reaction rate for CO ad oxidation is ca. 0.004 molecule site-1 s-1 which is 100 times smaller than the maximum rate for COad formation from methanol dehydrogenation; (ii) with increase in COad coverage from zero to 0.5 ML, the current efficiency of the indirect pathway for MOR increases and reaches ca. 17% under steady state. The general applicability of such a method is shortly discussed.
- Attenuated total reflection configuration
- Infrared spectroscopy
- Kinetic study
- Methanol oxidation
- Platinum electrode