A mechanism for aqueous proton transfer across graphene, through rare atomic defects, is described in Nature Communications this week. The identification of this mechanism could be an important step towards improving proton-selective membranes for fuel cell technology.
Computational studies have previously indicated that protons should not be able to pass through graphene at room temperature unless nanoscale holes or impurities are introduced, although recent experimental studies have demonstrated that transfer may be possible under the application of certain voltages.
Franz Geiger and colleagues placed a single layer of graphene on top of fused silica and passed an aqueous solution at varying pH across the graphene to see if any protons would pass through. The authors report that rare, naturally occurring atomic defects in graphene allowed selective, reversible proton transfer through the single graphene layer, at room temperature. They estimated that only a few of these defects per square micrometre of graphene are sufficient to allow rapid transfer. These findings may represent an important first step towards increasing fuel cell efficiency and the development of thinner, more selective membranes. However, accurate determination of the density of defects, especially in larger scale graphene, will be crucial in ruling out other mechanisms for proton transfer.