(520g) Construction of Robust Sub-2nm Channels for Fast Proton-Selective Transport in Flow Battery Membrane

Large-scale energy storage technologies, represented by the vanadium flow battery (VFB), provide a practical way to utilize clean energy resources. As one of the most critical components, the ion conductive membrane (ICM) isolates the reactive substances in the anode and cathode while conducting the protons to complete the current circuit. ICMs with robust sub-2-nm channels show high proton transport rates in flow battery, but it remains a great challenge to precisely control the ion sieving of the membranes.

Herein, as a promising proton-selective carrier, sulfonated piperazine covalent triazine framework (s-pCTF) with the channel size of ~1.5 nm and abundant fast proton hopping sites is introduced into sulfonated poly (ether ether ketone) (SPEEK) to fabricate advanced ICM for vanadium flow battery (VFB) application. The interior protoplasmic channels of s-pCTF demonstrate significant Donnan exclusion effect, resulting in an ultrahigh proton/vanadium ion selectivity (65.65×10⁴ S min cm^-3). Meanwhile, the nitrogen-rich sub-2-nm channels yield fast proton highway, and exterior-grafted sulfonic acid groups further facilitate the proton transfer, leading to a superior proton conductivity (30.9 mS cm^-1). By regulating the ion sieving and proton conductivity, the optimal hybrid membrane exhibits synchronously improved performance with an enhanced energy efficiency (92.41% to 78.53% at 40-200 mA cm^-2) and a long-term stability for 900 cycles over 400 h (EE: 87.2% to 85% at 120 mA cm-2) in VFB, outperforming pure SPEEK and Nafion212 membranes. This study validated the applicability of organic porous CTF with sub-2-nm channels and desired functionality in ICMs for high-performance VFB application.