One-atom-thick proton selective membranes

Monolayers of graphene and boron nitride with little to no defects are shown to allow only protons through them and block the transport of small ions. We exploit this property and employ graphene as an electrode to study water dissociation and electrolysis. An increase in the exchange current density is observed with increasing pH because the proton-selectivity of our graphene electrodes allows for spatial separation of proton-hydroxide pairs and so an increased electric field at zero-current is observed which accelerates water dissociation and at higher bias, full water electrolysis. The measured Tafel slopes in our alkaline regime for the hydrogen evolution reaction (or HER) do not change with pH and their values indicate that water dissociation becomes rate limiting due to the barrier associated with extracting the proton from water. These results have implications for alkaline electrolysers and are also relevant to the design of catalysts for HER in alkaline media. Finally, we use graphene to improve existing technology by incorporating CVD-grown graphene into the membrane of a proton exchange membrane fuel cell (PEMFC). Fuel crossover poses a significant problem for PEMFCs and leads to a reduction in performance. We demonstrate a significant decrease in hydrogen crossover with our scalable graphene-coated membrane.