| 초록 |
Commercial perfluorosulfonic acid type membranes (i.e Nafion) have been suffered from methanol crossover in the development of direct methanol fuel cells (DMFC), as the methanol crossover caused not only the depolarization at the cathode but loss of fuel. Methanol crossover phenomena of Nafion are understood as a result of large percolation size of water swollen perfluorosulfonic acid membranes. This mechanism is also the reason for high ion conductivity of Nafion, but this largely swollen passage of water allows unfortunately methanol to penetrate the Nafion membranes at the same time. Because methanol crossover and ion conductivity were somewhat tradeoff relationship, it was hard to prevent only the methanol crossover, maintaining high ion conductivity. A number of studies have been performed in order to develop alternative membranes, focusing on the reduction of methanol permeability. One main strategy was to develop new synthetic polymeric membranes that had ionic clusters possessing small percolation size. These included polyphosphazene, sulfonated polystyrene, polybenzimidazole, etc. Another approach was to modify commercial membranes to reduce methanol crossover. Surface modification is included in this strategy, as it has advantages in easy and simple chemical or physical treatment of commercially available membranes. Recent studies on surface modification involved the plasma treatment or plasma polymerization, electron beam treatment, and inorganic treatment. In this study, Nafion membranes were modified to reduce methanol permeability either by surface treatment or by bulk blending. Physical, chemical, and electrochemical properties of the membranes prepared were investigated. |
