Anhydrous Proton Conducting Polymer Electrolyte Membranes Via Polymerization-Induced Microphase Separation

Fuel cells utilizing proton conducting block polymer electrolytes could enable high-temperature, anhydrous operation. However, the performance of nanostructured block polymer electrolytes has been limited by poor mechanical stability and network defects in the conducting pathways. Here, we present the in-situ preparation of robust cross-linked polymer electrolyte membranes (PEMs) incorporating protic ionic liquids into one of the domains of a microphase-separated block copolymer. The facile design strategy involves reversible addition-fragmentation chain-transfer polymerization (RAFT) from a poly(ethylene oxide) RAFT chain transfer agent with styrene and cross-linkable divinylbenzene in the presence of a protic ionic liquid. The resulting transparent and robust PEMs exhibit a bi-continuous network morphology comprising poly(ethylene oxide)/protic ionic liquid conducting nanochannels and a cross-linked mechanical polystyrene scaffold. Long-range continuity of the conducting and mechanical domains result in excellent performance of the PEM with high mechanical and thermal stability. Furthermore, the elastic modulus approaches 10 MPa, with a high ionic conductivity of 15 mS/cm at 180 °C. This approach is very promising for scalable development and commercialization of PEMs for high-temperature fuel cell technologies.