Durability Improvements in PBI Membranes

Phosphoric acid (PA) doped polybenzimidazole membranes made by the PPA process have been the main focus of our research efforts for more than a decade.¹ These membranes exhibit an excellent combination of properties including high proton conductivities, excellent fuel cell performance, and long-term durability. For both fuel cell and hydrogen pump devices, the improvement in membrane mechanical properties at high temperatures could lead to further increases in durability and lifetimes of the membranes and resulting devices. We have been particularly interested in membrane compressive creep properties and have developed test protocols which are being used to understand the compressive creep properties and develop structure-property relationships for PPA processed membranes. In this work, we have investigated PBI copolymer membranes that showed higher mechanical properties (in particular, creep resistance) than homo-para-PBI membranes, and still possessed good proton conductivities at 180˚C under anhydrous conditions. Membrane electrode assemblies were prepared and tested in single cells to demonstrate long-term durability at different current densities and low phosphoric acid leaching rates. We will also discuss recent investigations in terms of hydrogen pumping applications, which may have broad applications in both emerging energy applications and current industrial gas markets.

1. L. Xiao; H. Zhang; E. Scanlon; L.S.Ramanathan; E.-W. Choe; D. Rogers; T. Apple; B.C. Benicewicz. Chem. Materials, 2005, 17, 5328-5333.