A hydrocarbon blend membrane consisting of an acidic polymer (sulfonated poly (ether ether ketone), SPEEK) and a basic polymer (polysulfone-2-amide-benzimidazole, PSf-ABIm) has been prepared and assessed in vanadium redox flow batteries (VRBs). The vanadium ion (VO)²⁺ permeability through the blend membrane is about 50 times lower than that of Nafion 117 and 4 times lower than that of the plain SPEEK. The Coulombic efficiency and energy efficiency of the single cell with the blend membrane are higher than those with Nafion and plain SPEEK membranes. The blend membrane also shows better chemical stability than plain SPEEK. The results demonstrate that blend membranes of this type are promising for VRBs.