Proton Transport in Hydrocarbon Membranes for Fuel Cell Applications

The nature of proton transport in various hydrocarbon membranes are investigated using the first-principles molecular dynamics simulations. Three hydrocarbon membranes, sulfonated poly ether sulfones (SPES), sulfonated poly(4-phenoxybenzoyl-1,4-phenylene) (SPPBP) and sulfonated poly (arylene ether ether nitile)s (SPAEENs) were studied in detail. Especially, we focus on the effects of various native chemical structure of the membranes on the transport of protons. We found that a hydrophillic functional group in those membranes can be protonated by accepting a proton when a hydronium ion (H₃O⁺) comes close to its vicinity. Such a result indicates that hydrophillic functional groups, such as a carbonyl group, affect the proton transport in a negative manner. The negative effects were found to be dominant under low hydration conditions.

Furthermore, it was observed that hydrophillic functional groups tend to attract water molecules, which, in turn, depletes hydration around the sulfonate group where such an effect hinders proton dissociation under low hydration conditions.