A pore-filling proton exchange membrane is fabricated by combining a porous polyethylene (PE) substrate and polybenzimidazole (PBI) resin for vanadium redox flow batteries (VRFB). The PE substrate not only optimized the structure of the composite membrane, but also significantly reduces its cost (<30$.m(-2)). Compared with Nafion212 and pure PBI membrane, PE/PBI composite membrane exhibits higher VRFB energy efficiency (88.62%-80.11%) in a current density range of 100-200 mA cm(-2). And within 150 cycles at 180 mA cm(-2), the composite membrane maintains stable charge-discharge performance with slower capacity decay rate, indicating a promising membrane candidate for VRFBs. (C) 2019 The Electrochemical Society.