Ultrahigh proton conductive nanofibrous composite membrane with an interpenetrating framework and enhanced acid-base interfacial layers for vanadium redox flow battery

Sulfonated poly(ether ether ketone)-based membranes containing amphoteric functionalized nanofibrous network ([email protected]) with the three-dimensional interlaced structure were developed, and the acid-base interaction between [email protected] and SPEEK constructs highly conductive proton channel and compatible interfaces. The large specific surface area and aspect ratio of nanofibers afford an orientated ion transmission channel along the fiber axis, bringing a high concentration of proton carriers and abundant hydrogen bonds to transfer proton. The S/[email protected] composite membrane displays superior proton conductivity (37.8 mS cm−1) to pristine SPEEK (16.4 mS cm−1) and Nafion 212 (28.0 mS cm−1). Owing to the interconnected network structure of [email protected] and the acid-base interactions, ion selectivity and chemical stability of the S/[email protected] composite membranes improve seriously. VRFB single cell with S/[email protected] membrane shows better voltage efficiencies (VE: 93.0–74.0%) and energy efficiencies (EE: 87.5–73.0%) than that of pristine SPEEK (VE: 86.0–60.2%, EE: 82.1–58.0%) and Nafion 212 membrane (VE: 88.0–67.0%, EE: 80.0–63.9%) at 60–200 mA cm−2. Meanwhile, S/[email protected] maintains a stable EE value of 80.0%, and no obvious decay after 500 cycles at 150 mA cm−2 appears, demonstrating its outstanding structural stability and durability. This opens a facile method to prepare the high-performance membrane by constructing the directional proton channels with functionalized nanofibers.