Characterization of Membrane Electrode Assembly for Fuel Cells Prepared by Electrostatic Spray Deposition

摘要

A novel electrocatalyst painting technique for realizing an extremely high yield of deposition in a limited surface area of a polymer electrolyte membrane has been developed by electrostatic spray deposition (ESD). First, a dispersion containing Pt/C powder and Nafion solution was sprayed by ESD. As a result, the dispersion was deposited on the entire surface area of a Nafion membrane placed on an Au counterelectrode, but not on the insulating poly(ethylene terephthalete) membrane. Second, for the highest-quality Pt/C catalyst layer, the solid content of the dispersion and the ejection rate were set to 3-4 wt % and 10-20 mm~3·min~(-1), respectively. The catalyst layer thus prepared demonstrated a fine, smooth structure. Third, in the case in which the sizes of the Nafion membrane and Au electrode were the same, the deposition occurred only on the Nafion/Au layered structure. This enabled an extremely high yield of deposition. The ESD of the Pt/C dispersion was conducted on a dry Nafion membrane with a water droplet on the surface. Consequently, an electrocatalyst layer was successfully formed only at the wetted point of the Nafion membrane. This technique enables the painting of the electrocatalyst layer over a limited area without the use of any surface masks. Finally, the membrane electrode assembly prepared by ESD was installed in a fuel cell and demonstrated as high a performance as that prepared by air-spraying. The cross-sectional morphology of the catalyst layer explained the coupling strength in the peel-off test well, as well as the dependence of current-voltage characteristics on catalyst layer thickness.