质子传导膜内受限空间离子扩散过程

摘要

To prove the feasibility that nano-scale porous membrane can replace ion exchange membrane used for vanadium redox flow battery (VRB), mass transfer of hydrated-ion in electrolyte solution through a limited space formed by PVDF nano-porous proton conductive membranes was studied. On a self-designed ion diffusion cell, NaCl and water permeation processes were measured under given concentration and hydrodynamic gradient, as well as osmotic pressure. The results obtained can be applied to correlate mass transport behaviors with membrane morphology. The results show that the behavior of ion diffusion through nano-scale limited space is similar to that in a bulk electrolyte solution; apparent diffusion coefficients are independent of ion concentration. In contrast, apparent diffusion coefficients of ion permeation through ion exchange membrane obviously increase with concentration gradient. For a given osmotic pressure, PVDF nano-porous proton conductive membranes have smaller water permeation rate than that of Nafion 117, and negative influence is also much smaller. Self-made PVDF proton conductive membrane can effectively reject VO2+ , providing selectivity over 300 for H+ /VO2+ electrolyte at ambient temperature, which means that it is possible to replace ion exchange membrane in flow battery application.%以具有纳米尺度孔径的聚偏氟乙烯(PVDF)质子传导膜为对象,研究电解质溶液中水合离子在受限空间内的传递行为,证明使用纳米尺度多孔膜代替离子交换膜用于液流电池过程的可行性.利用渗透实验分别研究浓度场、压力场,以及不同渗透压条件下膜中离子扩散和水迁移现象,分析传质行为与膜结构和组成之间的关系.结果表明离子在纳米尺度孔径的PVDF膜中的扩散过程与溶液中类似,表观离子扩散系数不受浓度差推动力的影响；离子交换膜中的表观离子扩散系数随浓度差推动力提高而增加.在渗透压作用下,自制PVDF纳米孔膜的水迁移速率低于Nafion 117膜,水迁移带来的负面影响更小；对于H+/VO2+的离子选择系数超过300,有效透过H+而阻止VO2+,适用于全钒液流电池过程.