Abstract
Creation of new membrane materials for proton exchange membrane fuel cells (PEMFCs) operating at elevated temperature and low relative humidity (RH) is one of the major challenges in the implementation of the fuel cell technology. New candidate membrane materials are required to efficiently conduct protons at 120oC and RH down to 15%. Based on these criteria, we are working on the development of new membrane materials, which are composites of inorganic proton conductors with a functionalized and cross-linkable Teflon-type polymer.
The synthesis of crosslinkable P(VDF-CTFE) copolymer with controllable structure, molecular weight and terminal and side chain silane groups was described in [1]. The chemistry of the synthesis was centered on a specifically designed functional borane initiator containing silane groups. The major role of polymer matrix is to
maintain the continuity of charge transfer and to ensure membrane integrity. The primary considerations include sufficient proton conductivity, thermal and chemical stability at elevated temperature, mechanical strength, compatibility with inorganic particulate phases, processibility to form uniform thin film, and cost effectiveness.
Several classes of inorganic proton conductors with high water retention capability, including mesoporous materials (sulfated and/or sulfonated alumina, zirconia, titania) and zirconium phosphate of different structure have been chosen as candidate components for the new composite membranes for PEMFC operation at elevated temperatures and reduced RH. The primary requirement to the inorganic phases is the ability to provide high proton conductivity with the minimum amount of water (reduced humidity).