Facile fabrication of holey graphene oxide paper bonded with sulfonic acid for highly efficient proton conduction

In this work, a novel holey graphene oxide bonded with sulfonic acid groups (S-HGO) was developed using a facile and eco-friendly strategy: erosion and oxidation of graphene oxide (GO) by H2O2 and sulfonation by 4-benzenediazoniumsulfonate. The freestanding paper fabricated by S-HGO shows a high proton conductivity of 4.97 × 10−2 S cm−1 at 60 °C and 100% relative humidity (RH), which is comparable to Nafion 115 (7.67 × 10−2 S cm−1) at the same condition. The holes on S-HGO provide shortcut channels for proton transfer across the GO nanosheet. The chemical-linked sulfonic acid groups afford additional hop sites for proton conduction and endow itself an enhanced thermostability. Under 100% RH and ambient pressure, the freestanding S-HGO deliver a peak power density of 103 mW cm−2 at a load current density of 273 mA cm−2, which is about three times more than that of GO at 35 °C. The results demonstrate that this S-HGO paper is a promising nanoscale inorganic material for proton exchange membranes.