The nanostructure is suitably formed into a nano-hair structure having a width of 1 to 1,000 nanometers and a length of 1 to 10,000 nanometers.
According to the inventors, it is possible to suitably increase the surface area of the polymer electrolyte membrane and, at the same time, suitably increase the hydrophobic properties of the surface of the polymer electrolyte membrane by forming nano-sized structures (nanostructures) such as nanohair or nanohole structures on the polyperfluorosulfonate polymer electrolyte membrane by plasma-assisted chemical vapor deposition (PACVD).
Moreover, it is possible to easily fabricate the membrane electrode assembly for a fuel cell by a simple process of directing coating platinum (Pt) catalyst on the nanostructured surface having increased surface area and hydrophobic properties by sputtering.
Since the surface of the polymer electrolyte membrane comprises the nanostructures such as nano-hair patterns, its surface area is suitably increased and, at the same time, the hydrophobic properties with respect to water are suitably increased. As a result, it is possible to considerably reduce the number of process of fabricating the membrane electrode assembly for a fuel cell and further reduce the amount of platinum catalyst.
FIG. 4A is a SEM image of the surface structure of a polymer electrolyte membrane after oxygen plasma treatment;
FIG. 5 is a SEM image showing nanohole structures formed on the surface of a polymer electrolyte membrane by argon plasma treatment at a bias voltage of -800 V for 1 minute, taken after depositing Pt catalyst on the surface of nanohole structures by sputtering;
FIG. 7A is a schematic diagram illustrating argon plasma treatment performed on the surface of a polymer electrolyte membrane at an oblique angle of 55.degree.;
The method includes the step of changing an angle formed between the plasma flow direction and the surface of the polymer electrolyte membrane, thus forming a plurality of nanostructures suitably inclined at a specific angle in one direction on the surface of the polymer electrolyte membrane.
The step of supporting or depositing catalyst on the surface of the polymer electrolyte membrane may be performed by selected spray coating, in which platinum or platinum catalyst particles are suitably supported on carbon black and then formed on an ion exchange membrane, or by screen coating, tape casting, dual ion-beam assisted deposition or sputter deposition, in which a surface of a polymer electrolyte membrane is suitably modified and then coated with platinum catalyst nanoparticles.