Carbon supported Ru–Se as methanol tolerant catalysts for DMFC cathodes. Part II: preparation and characterization of MEAs
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Cathode catalyst layers were prepared and characterized as part of membrane electrode assemblies (MEA) and catalyst coated membranes (CCM) on the basis of carbon supported methanol tolerant RuSe x catalysts. Preparation parameters varied were: catalyst loading (0.5–2 mg RuSe x cm−2), PTFE content (0, 6, 18 wt.%), carbon support (Vulcan XC 72 or BP2000), and fraction of RuSe x in the carbon supported catalysts (20, 44, 47 wt.%). The MEAs and cathode catalyst layers were electrochemically characterized under Direct Methanol Fuel Cell (DMFC) operating conditions by recording polarization curves, galvanostatic measurements, and impedance spectra. The morphology of the catalyst layers was investigated by means of confocal laser scan microscopy (CLSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) measurements. MEAs with Ru(44.0 wt.%)Se(2.8 wt.%)/VulcanXC72 cathode catalyst achieved the highest performance of all RuSe x catalysts investigated, i.e. ∼40 mW cm−2 at 80 °C under ambient pressure and λMeOH = λair = 4. This is 40% of the value obtained with commercial platinum cathode catalyst under the same operating conditions. The RuSe x catalysts investigated are stable over a period of more than 1,000 h. This was confirmed by TEM and XRD measurements, where no increase in mean RuSe x particle size (∼5 nm) after fuel cell operation was found. Enhancement of specific catalyst activity, mass transport, and active surface offer potential for a further improvement of RuSe x catalyst layers.
KeywordsRu-Se Methanol tolerant catalysts DMFC cathodes Surface roughness XRD CLSM SEM TEM
We thank H. Schmitz for performing the aging experiments, S. Chirayath for preparation of MEAs, T. Wüst for CLSM analysis and E. Loveless for proof-reading. The financial support of the Ministry for Education, Research and Technology BMBF in the frame of the network “O2-RedNet” (contract number 03 SF 0302) is gratefully acknowledged. We thank German Academic Exchange Service DAAD for financial support of S. Kaytakoglu.
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