Development of microreactor systems for electrocatalytic studies of methanol oxidation at elevated temperatures

Electro-oxidation of methanol to carbon dioxide is a complex heterogeneous reaction with several parallel pathways. Carbon monoxide produced as an intermediate in one of the reaction pathways poisons the catalyst by occupying active catalyst sites required for methanol oxidation. Other parallel reactions can produce partial oxidation products like formaldehyde and formic acid. A thorough understanding of the mechanism at the atomic scale and quantitative measurements of rates of individual reaction steps is necessary to design and tailor novel catalysts for Direct Methanol Fuel Cells (DMFC). While several half-cell studies have been performed at low temperatures and high anode overpotentials to elucidate the mechanism of methanol oxidation, very little is known about the mechanism or the rates of individual reaction steps at low anode overpotentials and higher temperatures where real fuel cells would operate.; Microreactors provide several advantages over conventional electrochemical cells for quantitative studies of methanol oxidation at high temperatures. In this work, we describe the design and development of microreactor systems to quantitatively measure reaction rates of individual reaction steps in the reaction mechanism. The microreactors are fabricated from silicon and pyrex substrates and contain integrated heaters, temperature sensors and electrodes. The microreactors have the capability to study, polycrystalline, single-crystal and supported catalysts. There are two versions of the microreactors: one to perform bench-top electrochemical experiments, and the other in which the microreactor can be interfaced with an Ultra High Vacuum (UHV) system and a Differential Electrochemical Mass Spectrometry (DEMS) system.; We report on the successful implementation of the bench-top microreactor system to study methanol electro catalysis at elevated temperatures. Initial studies on the temperature and potential dependence of the methanol electro-oxidation on thin film platinum electrodes are reported and results are discussed. Activation energies and transfer coefficients for the methanol electro-oxidation reaction have been measured and reported. We also report on room temperature measurements of rate constants for CO electro-oxidation on Pt(111). Flow experiments at room temperature have also been performed in the microreactor system to qualitatively explore parallel pathways leading to the formation of partial oxidation products.