Imidazole Tethered Styrene Backbone Polymers as Anhydrous Proton Conducting Membranes for High Temperature PEM Fuel Cells

摘要

Polymer e l e c t r o l y t e membrane (PEM) f u e l c e l l s a r e o f considerable interest for vehicle traction power sources. The currently used membrane materials require the presence of liquid water to provide sufficient conductivity for practical application. Complex heat and water management systems are required to keep the fuel cell stack under optimum conditions, which are expensive and take up too much volume to be easily accommodated in a light passenger car. A most attractive option would involve a true solid-state membrane material that contains no free solvent, can tolerate the presence of water, is conductive at low temperatures as well as high temperatures and can be tailored to provide desired gas permeability's for both the separator and the membrane-electrode assembly. The use of imidazole and its derivatives have been considered as the proton conducting medium instead of water in PEM fuel cells. The need to operate fuel cells at higher temperatures (120-150°C) has moved the operating conditions to a range where the remarkable properties of the perfluorosulfonic acids [PFSAs] no longer satisfy the requirements. An anhydrous p r o t o n c o n d u c t i n g system w i t h p r a c t i c a l p r o t o n conductivities for fuel cell separator membranes has been a challenge to realize. In the past decade, several studies have been conducted by different groups that have successfully achieved proton conductivities on the order of 10~(-3) S/cm at 200°C.The goal is to find an ideal match of practical proton conductivities in dry conditions, mechanical strength of the membrane and a T9 which is favourable. This paper will outline the syntheses, characterization and properties of polystyrene homopolymers and copolymers with tethered imidazole groups which are of interest for high temperature PEM fuel cell.