Greater selectivity and controls in the ion transport dynamics are essential in fields such as charge storage, separation, energy storage and conversion, neuromorphic computing and learning, electrochemistry, to name a few. Mechanistic insights into the intriguing hysteresis effects in the rectified electrokinetic transport through single conical nanopipettes are unveiled by combining time-resolved electroanalytical experiments with numeric simulation. Cations as counterions for surface charges are found to dominate not just the through-nanopore flux but also the hysteresis charges, that is, the net enriched or expelled charges during the transport process. Built on our earlier report on the through-nanopore ion flux dominated by counterions for surface charges, the “trapped ions” or hysteresis charges are analyzed herein. Cation selectivity is almost 100% in the hysteresis charges during the potential scans in low conductivity states driven by the combined applied and intrinsic surface electrical fields. Surprisingly, the cation selectivity in the total hysteresis charges remains high at 70–80% over a wide bulk concentration range in the high conductivity (HC) states, where higher ionic strength due to ion enrichment would decrease electrostatistic effects and thus ion selectivity. The retained high selectivity at HC is explained by the competition effects of electroosmotic flow against the co-ion migration. The respective cation and anion portions in the total hysteresis charges over a wide range of ionic strength and measurement conditions provide generalizable strategies for improvements in both transport throughput and selectivity.

中文翻译：

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通过锥形纳米移液管中的传输滞后选择性富集离子和电荷存储

离子传输动力学的更高选择性和控制对于电荷存储、分离、能量存储和转换、神经形态计算和学习、电化学等领域至关重要。通过将时间分辨电分析实验与数值模拟相结合，揭示了通过单个锥形纳米移液管的整流电动传输中有趣的滞后效应的机制见解。发现作为表面电荷的反离子的阳离子不仅支配通过纳米孔的通量，而且支配滞后电荷，即在传输过程中净富集或排出的电荷。基于我们之前关于表面电荷的反离子主导的通过纳米孔离子通量的报告，本文分析了“俘获离子”或滞后电荷。在由组合的应用和本征表面电场驱动的低电导率状态下的电势扫描期间，滞后电荷中的阳离子选择性几乎为 100%。令人惊讶的是，在高电导率 (HC) 状态下的宽体积浓度范围内，总滞后电荷中的阳离子选择性保持在 70-80% 的高水平，其中由于离子富集导致的较高离子强度会降低静电效应，从而降低离子选择性。HC 保留的高选择性可以通过电渗流对共离子迁移的竞争效应来解释。在宽范围的离子强度和测量条件下，总滞后电荷中的相应阳离子和阴离子部分为提高传输吞吐量和选择性提供了可推广的策略。