Pt/C-Electrocatalyst Painting on Polymer Electrolyte Membrane by Electrostatic Spray Deposition

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.