Data underlying research for A study on electrokinetic effects of spacers in ED using a segmented electrode stack

The boundary layer thickness within the fluid channels strongly determines the performance of electrodialysis (ED) processes since it controls the rate of ion transport. Reducing the boundary layer thickness through more efficient mixing allows for reducing the energy input to achieve the same current or higher currents for the same driving potential. In our previous work, we studied the electrokinetic effects of spacers within a lab-scale ED stack by using polyelectrolyte coated spacers that create an electro-osmotic mixing effect that affects the boundary layer near the limiting current regime. In this work, we use a segmented electrode stack to explore how spacer-induced electrokinetic effects impact the evolution of the boundary layer along the length of a stack operating under constant driving potential. By using the segmented electrode system, we are able to show clear differences in the distribution of current (densities) along the stack length between the case with polyelectrolyte-coated spacers and non-coated spacers. Our results show that the use of surface-charged spacers in particular leads to higher current densities in highly ion-depleted regions of the stack (i.e. farther towards the stack outflow) and we attribute this current density increase to increased electro-osmotic mixing within the boundary layer. Additionally, we quantify the difference in spacer performance between the uncoated and coated case using a simple empirical formulation for current density distribution along the stack length.

流体通道内的边界层厚度对电渗析（ED）工艺的性能起着决定性作用，因其直接调控离子传输速率。通过更高效的混合降低边界层厚度，可在相同驱动电势下减少能量输入，或在相同能量输入下实现更高电流。在前期研究中，我们借助可产生电渗流混合（electro-osmotic mixing）效应的聚电解质涂层隔板（polyelectrolyte coated spacers），该效应可影响极限电流区（limiting current regime）附近的边界层，对实验室规模电渗析堆内隔板的电动效应展开了研究。本研究采用分段电极堆（segmented electrode stack），探究在恒定驱动电势下运行的电渗析堆中，隔板诱导的电动效应对沿堆体长度方向边界层演化的影响。借助分段电极系统，我们得以清晰展示聚电解质涂层隔板与未涂层隔板两种工况下，沿堆体长度方向的电流（密度）分布差异。研究结果表明，表面带电隔板的使用尤其能提升电渗析堆离子耗竭区域（即更靠近堆体流出端的区域）的电流密度，我们将该电流密度提升归因于边界层内增强的电渗流混合作用。此外，我们通过沿堆体长度方向电流密度分布的简易经验公式，量化了未涂层隔板与涂层隔板的性能差异。