Abstract Monovalent ion selective membranes are permeable for monovalent ions while rejecting divalent ions to some extent. Different processes and applications like electrodialysis, microbial fuel cells, and flow batteries utilize such selective properties. Industrial membranes have a specific coating of equal charge to reject the bivalent counter ions. It has been suggested in the past that the current density regime at which such composite ion exchange membranes are operated can strongly influence their ion selectivity towards monovalent ions. Here, we now confirm this observation for a commercial CMS membrane as well as for a novel microgel modified membrane. The higher the applied current density is, the more acute the drop in selectivity becomes as opposed to the unmodified reference membrane where bivalent ions are transported preferentially. This work focuses on the relationship between selectivity and current density regime using (1) a conventional commercial membrane, (2) a commercial monovalent ion selective membranes as well as (3) a tailor-made selective membrane, the latter being surface-modified with quaternized Poly (2-vinylpyridine) (qP2VP) microgels. Experimental electrodialysis results in combination with (a) direct numerical simulations of mixed ion transport through the composite architecture and (b) a swelling analysis of the microgels by ellipsometry reveal that layer responsiveness and structural change of the modification layer is responsible for the decrease in permselectictivity upon an increased current density. The swelling reduces the charge density of the modification and therewith the rejection of divalent ions. It would be highly desirable to synthesize modification layers that have a low ion transport resistance while maintaining its volumetric charge density independent of the current density applied.

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关于带有离子选择性涂层的阳离子交换膜的选择性渗透性

摘要 一价离子选择性膜对一价离子具有渗透性，同时对二价离子有一定的排斥作用。不同的工艺和应用，如电渗析、微生物燃料电池和液流电池，都利用了这种选择性。工业膜具有等电荷的特定涂层以排斥二价反离子。过去已经提出，操作这种复合离子交换膜的电流密度范围可以强烈影响它们对单价离子的离子选择性。在这里，我们现在证实了商业 CMS 膜以及新型微凝胶改性膜的这一观察结果。施加的电流密度越高，与优先传输二价离子的未改性参比膜相比，选择性下降越剧烈。这项工作的重点是使用 (1) 传统商业膜，(2) 商业单价离子选择性膜以及 (3) 定制选择性膜，后者用季铵化聚（2-乙烯基吡啶）（qP2VP）微凝胶。实验电渗析结果与（a）通过复合结构的混合离子传输的直接数值模拟和（b）通过椭圆光度法对微凝胶的溶胀分析表明，改性层的层响应性和结构变化是导致渗透选择性降低的原因随着电流密度的增加。溶胀降低了改性的电荷密度，从而降低了二价离子的排斥。非常需要合成具有低离子传输阻力同时保持其体积电荷密度独立于施加的电流密度的改性层。