Poisoning of PtRu/C catalysts in the anode of a direct methanol fuel cell: a DEMS study

Poisoning of a commercial PtRu/C electrocatalyst with the products of methanol dehydrogenative adsorption has been studied in a membrane electrode assembly of a liquid fed direct methanol fuel cell at different electrode potentials in the temperature range between 30 and 110 degreesC using a newly designed DEMS setup. In all cases COads is identified as the stable methanol dehydrogenation product. The adsorbate coverage versus the electrode potential follows a bell-shaped curve, reaching a maximum around 0.1/0.2 V RHE. During methanol oxidation, the adsorbate coverage remains high and increases with temperature (theta similar to 0.6 at 90 degreesC in 1 M methanol solution). Kinetics of methanol adsorption has been studied at the open circuit potential (between 0 and 20 mV versus RHE). The coverage of the adsorbate and the rate of adsorption rise with temperature. The adsorption isotherms are of Temkin type with an adsorption rate constant k(ad) increasing from 1.6 +/- 0.1 cm(3) mol(-1) s(-1) at 30 degreesC to 73 +/- 11 cm(3) mol(-1) s(-1) at 110 degreesC and a temperature-dependent inhomogeneity parameter alphaf ranging from 35 +/- 1 at 30 degreesC to 8.3 +/- 0.2 at 110 degreesC. The apparent activation energy of methanol adsorption at the OCP and zero coverage is estimated as ca. 45 +/- 2 kJ mol(-1). (C) 2004 Elsevier Ltd. All rights reserved.