(220c) Hydroxylated Graphane : An Anhydrous Proton Exchange Membrane
Operating proton exchange membrane (PEM) fuel cells at higher temperatures is desirable for many reasons, namely increased tolerance of catalyst to CO poisoning and improved waste heat rejection. Traditionally, water facilitates the transport of protons in the PEM material and therefore imposes a limitation on the operating temperature of the fuel cell. We have designed a novel material based on graphane functionalized with hydroxyl groups. We show that this material can rapidly conduct protons under anhydrous conditions through a contiguous network of hydroxyl group hydrogen bonds. Density functional theory calculations predict remarkably low barriers to diffusion of protons along a 1D chain of surface hydroxyls. Diffusion is controlled by the local rotation of hydroxyl groups, a mechanism that is very different from that found in 1D water wires in confined nanopores or in bulk water. Completely hydroxylated graphane provides a 2D hydrogen bonded network, having more pathways for the diffusion of protons. A charge analysis reveals that the charge on the proton is essentially equally shared by all hydrogens bound to oxygens, effectively delocalizing the proton; this charge delocalization reduces the barrier to proton hopping. We have also investigated the influence of morphological and functional group defects to proton transport.