The purpose of this investigation was to compare catalysts produced by the Bönnemann -colloidal method (PtRu (B1) and PtRu (B2)), and those produced by the spontaneous deposition method (PtRu (SD)). The catalysts produced by both methods had good electrochemical behavior for methanol oxidation for proton exchange membrane fuel cell applications. The structure of the catalyst was examined by transmission electron microscopy (TEM). Energy dispersive spectroscopic analysis (EDS) was used to determine the semi-quantitative composition of the catalysts, and the electrochemical behavior was determined by cyclic voltammetry (CV). The diffractograms of the binary catalysts revealed platinum and ruthenium as the only crystalline phases, as per ICDD data base. The PtRu (B1) catalyst, treated in a reducing atmosphere, has the same structure as PtRu (B2), treated in an oxidising/reducing atmosphere, except that the crystallite size was around 1.7 nm for PtRu (B1) instead of 9.9 nm for PtRu (B2). The catalysts PtRu (B2) and PtRu (SD) showed similar cyclic voltammetric behavior, which was better than that of PtRu (B1). Both methods are suitable for the production of electrocatalysts for fuel cell applications. The colloidal method is more expensive than the deposition method, but the former permits the production of ternary and quaternary catalyst systems with enhanced CO tolerance.
This works report results of the structural and the electrochemical characterization of membrane electrode assemblies (MEA) for proton exchange membrane fuel cells (PEMFC) under various cell conditions using different MEA production processes. Electrochemical impedance spectroscopy (EIS) was applied "on-line" (in situ) as a tool for diagnosis concerning the cell performance. MEA with a 25-cm 2 surface area were prepared using Pt/C and Pt-Ru/C commercial electrocatalysts from E-TEK and Pt-Ru/C electrocatalysts produced by the alcohol reduction process. The catalytic ink was applied directly onto the carbon cloth or, alternatively, onto the Nafion® membrane. Two carbon cloth thicknesses were tested as diffusion layers in the MEA: 0.346 mm (common) and 0.424 mm (ELAT). An increase of the electrocatalytic activity can be obtained by pH control in the alcohol reduction process, possibly due to the better particle dispersion and the smaller particle sizes observed. In addition, a slower current decay in the ohmic region was observed using the thinner carbon cloth. This can be related to a lower resistance of the gas flow through the cloth to the catalytic active layer. Different types of methanol feed were employed in the experiments: by humidification and by evaporation. The results showed that the choice of suitable methods for catalyst preparation as well as for MEA production enhance PEMFC performance.
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