Simple acid etched graphene oxide constructing high-performance sandwich structural hybrid membrane for redox flow battery

As a promising large-scale energy storage technology, vanadium redox flow battery (VRFB) encounters severe permeation of vanadium ions, originating from the most widely used commercial perfluorosulfonic acid (PFSA) membrane. Here, a simple acid etching strategy is used to prepare highly hydrophilic defective graphene oxide (d-GO) nanosheets and then is introduced to the PFSA matrix to effectively suppress vanadium ions permeation, owing to the bent or prolonged diffusion path induced by the d-GO nanosheets. The good hydrophilicity of the d-GO nanosheets shortens the paths of proton transportation enhancing proton conductivity. Based on that, a hybrid membrane with sandwiched structure is fabricated, which contains the d-GO-modified PFSA as skin, and porous polytetrafluoroethylene (PTFE) is used as the core layer to enhance the membrane stability. With the combination of the d-GO nanosheets and the porous PTFE, this hybrid membrane endows the VRFB with superior Coulombic efficiency (∼97.0%) and high energy efficiency (∼86.9%) at 120 mA cm−2. Both are much higher than those of the commercial one and most of the previous reports in PFSA-based membrane for VRFB. This study proposes an effective strategy to obtain a high ion-selective membrane for VRFB and may also inspire other fields.