Constructing Anhydrous Hydrogen-Bonding Network in a Sulfonated Polymer Based Membrane for High Temperature Fuel Cell Applications

Abstract

Proton exchange membrane fuel cells (PEMFCs) are most promising clean powers for vehicles.1 Current PEMFCs relying on Nafion with water necessary for proton conduction can only work below 363 K owing to that Nafion loses its conductivity quickly in response to the inevitable evaporation of water at elevated temperatures. However, PEMFCs operating at temperatures higher than 423 K are highly desired to overcome many obstacles of present PEMFCs, such as slow reaction kinetics, CO poisoning of the electrode catalysts, and the complexity of water and heat managements.2-4 Great efforts have been paid to develop anhydrous PEMs for these high-temperature FCs, particularly, those based on inorganic acids possessing intrinsic high proton conductivities at above 423K have been extensively studied.3,4 Intermingling sulfonated polymers (SPs, such as Nafion) with non-volatile, thermally stable (up to 573 K) ionic liquids (ILs) for anhydrous PEMs has also attracted numerous attention, and ionic conductivities exceeding 10-2 S cm-1 have been reached. However, these PEMs often suffer from low proton transfer numbers (0.5~0.6), poor mechanical performanc, and the assembed H2-O2 FCs with these ILs based PEMs were often poor in performance at intermediate temperatures.5,6 Here we report an anhydrous hydrogen-bond fusing strategy for high-performance PEMs by introducing hydroxyl functionalized IL (IL-OH) into the SPs. The IL-OHs selected as both proton donators and acceptors, that are evidenced to be strongly hydrogen-bonded with both Nafion and some nano-inorganic matters. Consequently, an effective interconnected hydrogen-bond network forms in a HFIL/SP based hybrid membrane, endowing the PEM with robust mechanical and thermal stability. At temperatures >430K , the anhydrous ionic conductivity of this kind of PEM can reach higher than 50 mS cm-1 with a large proton transfer number close to 1. And the initial high performance of the assembled intermediate-temperature H2-O2 FCs showed promising applications of this new generation HFIL/SP PEMs.