Ionic Conductance Through Graphene: Assessing Its Applicability as a Proton Selective Membrane.

Inspired by recent report on possible proton conductance through graphene we have investigated the behavior of pristine graphene and defect engineered graphene membranes for ionic conductance and selectivity with the goal of evaluating a possibility of its application as a proton selective membrane. The averaged conductance for pristine CVD (chemical vapor deposited) graphene at pH1 is ~ 4 mS/cm2 but varies strongly due to contribution from the unavoidable defects in our CVD graphene. From the variations in the conductance with electrolyte strength and pH, we can conclude that pristine graphene is fairly selective and the conductance is mainly due to protons. Engineering of the defects with ion beams (He+, Ga+) irradiation, and plasma (N2 and H2) treatment showed improved areal conductance with high proton selectivity mostly for He-ion beam and H2 plasma treatments, which agrees with primarily vacancy-free type of defects produced in these cases confirmed by Raman analysis.