Electrochemical and impedance spectroscopy studies in H2/O2 and methanol/O2 proton exchange membrane fuel cells

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-cm2 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