AVS 50th International Symposium
    Electrochemistry and Fluid Solid Interfaces Tuesday Sessions
       Session EC+SS-TuM

Paper EC+SS-TuM1
A Microreactor System for Electrocatalytic Kinetics: Methanol Oxidation on Platinum Electrodes at Elevated Temperature

Tuesday, November 4, 2003, 8:20 am, Room 326

Session: Water at Interfaces I: Structure and Electrochemistry
Presenter: N. Arvindan, University of Washington
Authors: N. Arvindan, University of Washington
L. Arnadottir, University of Washington
E.M. Stuve, University of Washington
Correspondent: Click to Email
We describe a silicon-based microreactor for measurement of electrocatalytic rate constants for methanol oxidation on platinum and modified platinum electrodes. The device consists of silicon and pyrex wafers bonded together by a Teflon treatment to create an enclosed flow channel 0.25 mm deep, 1.5 mm wide, and 25 mm long. The flow channel includes deposited platinum lines for fluid heating, temperature measurement, and a counter electrode. A separate palladium line serves as a reference electrode. The working electrode is inserted into an opening in the flow channel. The working electrode can be a single crystal, polycrystalline sample, or actual supported catalyst. The microreactor can accommodate mixed metallic catalysts such as PtRu. Methanol oxidation is measured at constant potential following a step from a non-reacting potential. Accumulation of surface species like CO is subsequently measured by linear sweep voltammetry. These two measurements enable the overall oxidation rate of methanol to be compared with the CO oxidation rate. Reaction studies over the range of 80 to 100 °C show that methanol oxidation occurs at the same rate as CO oxidation, consistent with the series reaction path (methanol to CO to carbon dioxide) being the dominant mechanism. The results conclusively show that thermal desorption of CO is insignificant, even at temperatures as high as 95 °C. At 95 °C turnover rates vary from 0.1 to 1 per second for the respective potential range of 400 to 600 mV vs. RHE. These results show that unmodified polycrystalline platinum is an effect catalyst for methanol oxidation at 95 °C and support the feasibility of high temperature direct methanol fuel cells.