ABSTRACT
ABSTRACT Electro-oxidation of methanol to CO2 on platinum electrodes is plagued by accumulation of CO, which poisons the reaction. The mechanism for CO2 production has not been resolved with claims of a serial path (involving adsorbed CO) or a parallel path (non-CO pathway) being advanced. In this chapter, we test the hypothesis that a non-CO path (the parallel path) exists for methanol electro-oxidation on a Pt(111) electrode in perchloric acid electrolyte. The experiments, which were performed in an anaerobic dual-cell apparatus at room temperature, consisted of chronoamperometry (for reaction times between 0.03 and 300 s at 0.6 V) and linear sweep voltammetry. The experimental results confirm the existence of both the serial and the parallel path mechanisms at 0.6 Vand show that a simplified representation of the surface chemistry is inadequate to explain all the results. We developed a Langmuir-Hinshelwood kinetic model incorporating both pathways and fitted the experimental data over the entire range of the reaction time. The model, which contains four kinetic and four mechanistic parameters, reveals that the reactive intermediate in the non-CO path has the stoichiometry H:C:O before reacting to CO or CO2. At steady state at 0.6 V, the parallel path accounts for 75% of the CO2 produced, and the CO coverage is 0.29 monolayers. Small changes in CO coverage produce an amplified response of the overall reaction rate by controlling the surface sites available for reaction through the parallel path.
