论文标题
不对称性在价值和扩散率对带电圆柱孔中二元电解质的运输的影响
Impact of Asymmetries in Valences and Diffusivities on the Transport of a Binary Electrolyte in a Charged Cylindrical Pore
论文作者
论文摘要
多孔介质中的离子传输都存在于许多技术中,例如电池和超级电容器等储能设备,以及电化学碳捕获和电容式脱位等环境技术。关于平板电极的最新研究表明,离子特性(例如价和扩散性)中的不对称性会导致有趣和反直觉的物理现象。然而,在多孔几何形状中很少探索这种不对称运输的后果。为了弥合这一知识差距,我们在圆柱孔中进行了泊松 - 静脉planck方程的扰动膨胀,该孔对具有任意价值和扩散率的二元电解质的小电位极限。我们在扰动分析和直接数值模拟之间获得了良好的一致性。我们的分析表明,电荷和盐的运输是相互耦合的。此外,随着离子的价和扩散性不对称性的增加,电荷和盐转运过程之间的耦合得到了增强。我们观察到,离子扩散性的不匹配会诱导非平凡的盐动力学,从而产生毛孔中盐的短暂耗竭或增强盐。在高静态扩散层电导的状态下,我们获得了扰动模型的分析解决方案。溶液阐明了电解质不对称的方式诱导两个由相对孔径设定的充电时间尺度。在重叠的双层状态中,这些时间尺度减少到每个离子的扩散时间,从而使两个离子的传输似乎被解耦。总体而言,我们的工作强调了阳离子和阴离子扩散的不对称性从根本上改变了带电的圆柱孔内离子传输的行为,并开辟了有关多孔材料电解质传输的新研究途径。
Ion transport in porous media is present in a wealth of technologies, e.g., energy storage devices such as batteries and supercapacitors, and environmental technologies such as electrochemical carbon capture and capacitive deionization. Recent studies on flat-plate electrodes have demonstrated that asymmetries in ion properties, such as valences and diffusivities, lead to intriguing and counter-intuitive physical phenomena. Yet, the consequences of such asymmetries to ion transport have seldom been explored in porous geometries. To bridge this knowledge gap, we conduct a perturbation expansion of the Poisson-Nernst-Planck equations in a cylindrical pore in the limit of small potentials for a binary electrolyte with arbitrary valences and diffusivities. We obtain good agreement between the perturbation analysis and direct numerical simulations. Our analysis reveals that the charge and the salt transport are coupled with each other. Further, the coupling between the charge and salt transport processes is enhanced with an increase in valence and diffusivity asymmetries of ions. We observe that the mismatch of the ionic diffusivities induces a non-trivial salt dynamics, producing either transient depletion or enhancement of salt in the pore. In the regime of high static diffusion layer conductance, we obtain an analytical solution to our perturbation model. The solution elucidates how electrolyte asymmetry induces two charging timescales that are set by the relative pore size. In the overlapping-double-layer regime, these timescales reduce to the diffusion times of each ion such that the transport of the two ions appears to be decoupled. Overall, our work underscores that the asymmetry in cation and anion diffusivities fundamentally alters the behavior of ionic transport inside a charged cylindrical pore and opens up new avenues of research on electrolyte transport in porous materials.