Abstract:

To solve the balance between proton conductivity and ion selectivity and the balance between power density and capacity decay in vanadium flow battery (VFB), a series of continuous covalent organic framework/ polyether sulfone (COF/PES) composite membrane with size-sieving effect were designed and prepared. The COF nanosheets synthesized by interfacial polymerization were fabricated into continuous proton/vanadium ion sieving COF layers on the PES support layer by vacuum assisted self-assembly. The regular rigid skeleton of COF layer endows the composite membrane with extremely low swelling ratio, and the uniform sub-nanoscale ion transport channel (pore size is about 0.6 nm) constructed by orderly staggered stacking of nanosheets has accurate size-sieving effect on H⁺/V ⁿ⁺ ions. The vanadium permeability of COF/PES composite membrane is only 0.61 × 10^-8 cm^-2·s^-1, and the ion selectivity is 4.0 times that of Nafion 212. At 80 mA·cm^-2, the energy efficiency of composite membrane reaches 82.9%, which is better than Nafion 212 (81.2%). In the long cycle test at 100 mA·cm^-2, the capacity retention rate of the VFB equipped with composite membrane was 16.2% higher than that of the battery equipped with Nafion 212, indicating that the continuous COF/PES size-sieving composite membrane has broad application prospect in vanadium flow battery.

Key words: covalent organic framework, size-sieving, vanadium flow battery, membrane, ion exchange, electrochemistry

摘要：

设计了应用于全钒液流电池的尺寸筛分效应共价有机框架/聚醚砜(COF/PES)复合膜，利用纳米片的有序交错堆叠在聚醚砜支撑层上构建了具有均匀埃米级离子传输通道的连续COF分离层。连续COF层的规整刚性骨架赋予了膜极低的溶胀比，有序的埃米级孔道(有效孔径约为0.6 nm)对氢/钒离子具有精确的尺寸筛分作用。COF/PES筛分复合膜的钒渗透率仅有0.61×10^-8 cm^-2·s^-1，质子/钒离子选择性为Nafion 212的4.0倍。电流密度为80 mA·cm^-2下复合膜的能量效率达到82.9%，优于Nafion 212(81.2%)。100 mA·cm^-2下的长循环测试中，复合膜电池容量保持率相比于Nafion 212电池提高了16.2%，表明连续COF/PES筛分复合膜在全钒液流电池中具有广阔的应用前景。

关键词: 共价有机框架, 尺寸筛分, 全钒液流电池, 膜, 离子交换, 电化学