Discharging dynamics in an electrolytic cell
Discharging dynamics in an electrolytic cell
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DOI：
10.1103/physreve.94.012601
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发表时间：
2016-07-05
影响因子：
2.4
通讯作者：
Khair, Aditya S.
中科院分区：
文献类型：
--
作者：
Feicht, Sarah E.;Frankel, Alexandra E.;Khair, Aditya S.
我们分析了一个放电电解池的动力学组成的二元对称电解质之间的两个平面，平行的阻断电极。当最初施加电压时，电解质中的离子向电极迁移，形成双电层。在系统达到稳定状态并且外部电流衰减到零之后，关闭所施加的电压并且电池放电，离子最终返回到均匀的空间浓度。在近似于或等于25 mV的热电压V-T = k（B）T/q的电压下，其中k（B）是玻尔兹曼常数，T是温度，q是质子的电荷，对表面活性剂掺杂的非极性流体的实验观察到，在充电和放电期间外部电流的时间演变是不对称的[V. Novotny和M. A. Hopper，J. Electrochem. Soc.126，925（1979）; P. Kornilovitch和Y. Jeon，J.Appl.Phys.109，064509（2011）]。事实上，在足够大的电压（几个V-T）下，放电期间的电流不再是单调的：它在幅度衰减到零之前显示出“反向峰”。我们分析放电的动力学通过解决泊松-能斯特-普朗克方程的离子传输通过渐近和数值技术在三个制度。首先，在“线性状态”中，当施加的电压V形式上远小于V-T时，充电和放电电流在时间上是反对称的;然而，充电和放电期间的电势和电荷密度分布是不对称的。电流演变是在电池的RC时间尺度上，λ L-D/D，其中L是电池的宽度，D是离子的扩散率，并且λ（D）是德拜长度。第二，在（实验相关的）薄双层极限中，λ = λ（D）/L > V-T ln（1/λ）。我们提供了半解析表达式的饱和反向峰值时间和电流，它可以用来推断电荷载流子的扩散率和浓度从实验。
We analyze the dynamics of a discharging electrolytic cell comprised of a binary symmetric electrolyte between two planar, parallel blocking electrodes. When a voltage is initially applied, ions in the electrolyte migrate towards the electrodes, forming electrical double layers. After the system reaches steady state and the external current decays to zero, the applied voltage is switched off and the cell discharges, with the ions eventually returning to a uniform spatial concentration. At voltages on the order of the thermal voltage V-T = k(B)T/q similar or equal to 25 mV, where k(B) is Boltzmann's constant, T is temperature, and q is the charge of a proton, experiments on surfactant-doped nonpolar fluids observe that the temporal evolution of the external current during charging and discharging is not symmetric [V. Novotny and M. A. Hopper, J. Electrochem. Soc. 126, 925 (1979); P. Kornilovitch and Y. Jeon, J. Appl. Phys. 109, 064509 (2011)]. In fact, at sufficiently large voltages (several V-T), the current during discharging is no longer monotonic: it displays a "reverse peak" before decaying in magnitude to zero. We analyze the dynamics of discharging by solving the Poisson-Nernst-Planck equations governing ion transport via asymptotic and numerical techniques in three regimes. First, in the "linear regime" when the applied voltage V is formally much less than V-T, the charging and discharging currents are antisymmetric in time; however, the potential and charge density profiles during charging and discharging are asymmetric. The current evolution is on the RC timescale of the cell, lambda L-D/D, where L is the width of the cell, D is the diffusivity of ions, and lambda(D) is the Debye length. Second, in the (experimentally relevant) thin-double-layer limit epsilon = lambda(D)/L > V-T ln(1/epsilon). We provide semi-analytic expressions for the saturated reverse peak time and current, which can be used to infer charge carrier diffusivity and concentration from experiments.