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 mm3·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.

An electrocatalyst painting technique for use in a limited surface area of a polymer electrolyte membrane has been developed by employing electrostatic spray deposition (ESD). ESD is a process in which an aerosol of a solution is ejected from a metal syringe nozzle with a high applied voltage under atmosphere to obtain a thin film on the counter electrode. First, a dispersion containing Pt-loading carbon (Pt/C) powder and Nafion solution was sprayed by using the ESD technique. As a result, the dispersion was deposited over the entire surface area of a polymer electrolyte membrane of Nafion that was placed on the counter Au electrode, whereas, the dispersion was neither deposited on an electric-insulating poly(ethylene telephthalete) (PET) nor on the Nafion membrane on the PET. For the experiment, the Nafion membrane was pretreated to give it ionic conductivity. Next, a dye solution containing Rhodamine B was sprayed in the same manner, with the same result. In the case where the sizes of Nafion membrane and Au electrode were the same, the deposition only occurred on the Nafion/Au layered structure. According to these results, the aerosol generated at the syringe nozzle is introduced to the conductive area and kept away from the insulating area. Finally, for the untreated Nafion membrane on which a water droplet was placed, ESD of the Pt/C dispersion was conducted. Consequently, an electrocatalyst layer was successfully formed only at the wetted point of the Nafion membrane. This technique enables the painting of an electrocatalyst layer over a limited area without the use of any surface mask.

The electrocatalyst layer of polymer electrolyte fuel cells(PEFCs) formed a three-phase interface by using a mixture of Pt/C and a proton-conductive polymer. In the case where Nafion was used as a proton-conductive polymer, some extent of platinum particles of Pt/C were covered by a insulation property cluster of Nafion ; therefor, an efficient formation of the threephase interface was not achieved. In the present study, polyelectrolyte complex(PEC) was used with Pt/C instead of Nafion. PEC, which has a small cluster size, could be expected not to cover the Pt particle. An electrode catalyst layer consisting of the Pt/C and a PEC was prepared on an Au flag electrode. The platinum utilization efficiency was measured by cyclic voltammetry. As a result, it was found that the Pt surface area of the Pt/C-PEC was 1.5-times larger than that of Pt/C-Nafion.

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