Covalent/ionic co-crosslinking constructing ultra-densely functionalized ether-free poly(biphenylene piperidinium) amphoteric membranes for vanadium redox flow batteries

摘要: Abstract A novel covalently/ionically co-crosslinked poly(biphenylene piperidinium) amphoteric membrane was designed for improved stability and efficiencies in vanadium redox flow batteries (VRFB). The amphoteric-side-chain structure provides an ultrahigh functionalization degree (4.93 mmol·g − 1) unobstructed ion channels, which endowed the with excellent conduction capacity comparable to Nafion 212 (area resistance: 0.23–0.29 Ω·cm2). Surpassing traditional sulfonated membranes single ionic crosslinked membranes, even at high level functionalization, co-crosslinking structures guaranteed a low swelling ratio (10.1%) VO2+ permeability of 0.79 × 10−8 cm2·s − 1. Moreover, due lack sensitive aryl ether bonds, these showed very good chemical stability, slight mass loss 3.43% (nearly 5.5 times lower than SPEEK) after soaking oxygen species 30 days. On this basis, exhibited battery performance. Coulombic, voltage, energy using above reached 98.12, 87.27, 85.98% 120 mA·cm−2 current density no obvious decline occurred 400 cycles. self-discharge time up 136 h. These observations indicated that appeared promising use VRFB applications.