  An ideal proton exchange membrane should only permeate protons and be leak
tight for fuels. Graphene is impermeable to water and poorly conducting to
protons. Here, we chemically functionalized monolayer graphene to install
sulfophenylated sp3 dislocations by diazotization. Selective to protons,
transmembrane areal conductances are up to ~50 S/cm2, which is ~5000 fold
higher than in pristine graphene. Mounted in a direct methanol fuel cell,
sulfophenylated graphene resulted in power densities up to 1.6 W/mg or 123
mW/cm under standard cell operation (60 C), a value ~two-fold larger than
micron-thick films of Nafion 117. The combination of sp3 dislocations and polar
groups, therefore, allow the creation of hydrophilic ion paths through graphene
and unveils a novel route to rationalize transmembrane hydron transport through
2D materials.
