Construction of Surface Sulfonic and Amino Acid–Base Pair Modified Graphene Oxide for Effectively Promoting the Selectivity of the Proton Exchange Membrane

Surface −SO3H and −NH2 acid–base pair modified graphene oxide (BAGO) was constructed by first polydopamine (PDA) coating onto GO and subsequent reaction with 2,2′-benzidinedisulfonic acid (BA). The composite proton exchange membrane (PEM) with prominently elevated selectivity (selectivity: the ratio of proton conductivity to methanol permeability) was prepared by incorporation of BAGO into the Nafion matrix. The functional groups (−SO3H and −NH2) onto BAGO could form consecutive acid–base pairs for proton transfer benefitting from the tethering function of GO and the interconnection of the functional groups. In addition, continuous acid–base pair proton conducting pathways could be constructed between −NH2 of BAGO and −SO3H of Nafion. These enormously expedited the proton transportation of the composite PEM, enabling its proton conductivity to reach 0.262 S cm–1 under 95% RH, 90 °C, twice that of the recast Nafion (RN). Furthermore, significantly attenuated methanol permeability was achieved by the composite PEM due to the methanol barrier effect of BAGO and reduced free volume of the composite PEM. Meanwhile, the maximum power density of the composite PEM in a direct methanol fuel cell reached 32.5 mW cm–2, approximately 62% larger than that of RN (20.1 mW cm–2). This work offers a valuable guidance for constructing the composite PEM with effectively improved selectivity.