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°C using a newly designed DEMS setup. In all cases CO_ads is identified as the stable methanol dehydrogenation product. The adsorbate coverage versus the electrode potential follows a bell-shaped curve, reaching a maximum around 0.1/0.2V RHE. During methanol oxidation, the adsorbate coverage remains high and increases with temperature (θ ∼ 0.6 at 90°C in 1M methanol solution). Kinetics of methanol adsorption has been studied at the open circuit potential (between 0 and 20mV 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 ± 0.1cm³mol^-1s^-1 at 30°C to 73 ± 11cm³mol^-1s^-1 at 110°C and a temperature-dependent inhomogeneity parameter αf ranging from 35 ± 1 at 30°C to 8.3 ± 0.2 at 110°C. The apparent activation energy of methanol adsorption at the OCP and zero coverage is estimated as ca. 45 ± 2kJmol^-1.