(A) study on the modification of Nafion membrane using poly(4-vinyl pyridine) for DMFC

Abstract

Fuel Cell converts chemical energy of fuel into electrical energy with high efficiency and low emission of pollutants. Among many types of fuel cells, Direct Methanol Fuel Cell is interesting for the mobile and domestic application due to low operating temperature, no leak problem, and fast start-up and easy fuel storage and transportation. Perfluorinated membrane such as Nafion(from Du-pont) has been used as the polymer electrolyte membrane. Nafion has good conductivity and thermal, mechanical properties. But Nafion can not be used for DMFC due to high methanol crossover. In this thesis, Nafion 117 membrane which was usually used as the electrolyte membrane for PEMFC was modified by using poly(4-vinyl pyridine) to reduce the methanol crossover, which cause fuel losses and lower power efficiency, by the formation of Ionic crosslink structure (sulfonic acid-pyridine complex) on the Nafion 117 surface. Nafion film was immersed in P4VP/NMP solution. P4VP weight% of modified membrane was controlled by changing the concentration of P4VP/NMP solution and the dipping time. P4VP weight% increased with increasing of concentration of dipping solution and dipping time. Modified Nafion membranes had thin P4VP layer after dip coating and the thickness of coating layer increased due to the penetration of P4VP solution. The thickness of P4VP layer increased with increasing of the concentration of the dipping solution and the dipping time when the concentration of dipping solution was low. But in high P4VP concentration, the thickness of the P4VP layer was nearly constant due to the formation of acid-base complex which interrupted the penetration of P4VP. FT-IR results showed that P4VP could penetrate up to 30μm of Nafion 117 membrane. Proton conductivity and methanol permeability of modified membrane were lower than those of Nafion 117. The trend of proton conductivity and methanol permeability was similar. Both decreased with increasing the concentration of the dipping sol...