Acid-base block copolymer brushes grafted graphene oxide to enhance proton conduction of polymer electrolyte membrane

Abstract

For composite membrane, efficient mass transfer between polymer and filler can trigger synergic promotion effect through the tunable interfacial nanodomains. Herein, four kinds of functionalized graphene oxide nanosheets (FGOs) bearing polymer brushes (phosphoric acid brushes, imidazole brushes, acid-base or base-acid block copolymer brushes) are designed exquisitely, and then embedded into two typical polymer matrixes (acidic sulfonated poly(ether ether ketone) and basic chitosan) to prepare composite membranes. It is found that the strong electrostatic attractions drive the brushes insert into polymer matrix and form interconnected networks, affording enhanced thermal/mechanical stabilities and enlarged free volume. Especially, the attractions from outer segment even drag the inner segment to deeply insert into polymer matrix for FGOs with acid-base copolymer brushes, yielding wide and long-range interfacial networks. When employing as proton conductors, these networks can ultrafast transport protons between FGOs and polymer matrix using the functional groups (especially acid-base pairs), affording 6.7 times’ increment of proton conductivity to polymer membrane. The synergic promotion effect is governed by the width and amount of interfacial networks (pathways). The effect of these polymer brushes on acidic membrane and basic membrane are investigated and compared extensively to explore their functions on membrane microstructure and mass transfer.