Synthesis of Polymer Electrolyte Membrane based on Poly(phenylene oxide) with Phosphonic Acid for Low Humidity Condition

Abstract

There are many researches for fuel cell which is operated under the low humidity condition. In this condition, a new material enabling to transport protons in the anhydrous state is needed. In general, under the low humidity condition, proton is transported by hydrogen bonding. Grotthus and self-dissociation mechanism of phosphonic acid is suitable to deliver protons in that situation. In this work, the polymer electrolyte membrane which has phosphonic acid in the side chain is synthesized. It is exploited to evaluate an effect of length of side chain on proton conductivity. Among these polymers, the longest side chain contained polymer shows highest proton conductivity under 80 ℃ and 30% in relative humidity (RH) condition, while it has a lowest water uptake (4.4%) and swelling ratio (2.4%). The reason is that the long side chain is more suitable for hydrophilic/hydrophobic phase separation and it is confirmed by TEM.