It is believed that ion current rectification (ICR), a property that assures preferential ionic transport in one direction, can only be observed in nanopores when the pore size is comparable to the thickness of the electric double layer (EDL). Rectifying nanopores became the basis of biological sensors and components of ionic circuits. Here we report that appreciable ICR can also occur in highly charged conical, polymer mesopores whose tip diameters are as large as 400 nm, thus over 100-fold larger than the EDL thickness. A rigorous model taking into account the surface equilibrium reaction of functional carboxyl groups on the pore wall and electroosmotic flow is employed to explain that unexpected phenomenon. Results show that the pore rectification results from the high density of surface charges as well as the presence of highly mobile hydroxide ions, whose concentration is enhanced for one voltage polarity. This work provides evidence that highly charged surfaces can extend the ICR of pores to the submicron scale, suggesting the potential use of highly charged large pores for energy and sensing applications. Our results also provide insight into how a mixture of ions with different mobilities can influence current–voltage curves and rectification.

中文翻译：

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带有高电荷孔壁的介孔中电压诱导的离子浓度调制和离子电流整流

据信，仅当孔径与双电层（EDL）的厚度相当时，才能在纳米孔中观察到确保电流在一个方向上优先迁移的离子电流整流（ICR）。整流纳米孔成为生物传感器和离子电路组件的基础。在这里，我们报道，在尖端直径高达400 nm的高电荷锥形聚合物中孔中，也可能出现明显的ICR，因此比EDL厚度大100倍以上。考虑到孔壁上功能性羧基的表面平衡反应和电渗流的严格模型被用来解释这种意想不到的现象。结果表明，孔的精馏是由于表面电荷的高密度以及高迁移性氢氧根离子的存在而引起的，氢氧根离子的浓度在一种电压极性下得到增强。这项工作提供了证据，证明高电荷的表面可以将孔的ICR扩展到亚微米级，这表明高电荷的大孔在能量和传感应用中的潜在用途。我们的结果还提供了对具有不同迁移率的离子混合物如何影响电流-电压曲线和整流的见解。