Capacitive deionization (CDI) is an effective method for desalination of brackish water to alleviate the global freshwater crisis. Obtaining high desalination capacity is the primary focus of this field. Based on capacitive and pseudocapacitive behavior of the electrodes, current research is mainly devoted to increasing the specific surface area of electrode materials, however, the NaCl adsorption capacity is typically limited to the range of 10–20 mg g⁻¹. In this work, we propose a new design paradigm of using a vertical-aligned nanotubular structure for CDI. This design allows ions to be temporarily held inside the electrodes like ships docked in a harbor (ion-docking effect, IDE) due to the greatly diminished water flow inside the tubes, thus enhancing the desalination capacity. As a result, the obtained CDI device based on vertical-aligned nanotubular P-TiO₂ arrays shows an ultra-high NaCl adsorption capacity of ~60 mg g⁻¹ within 30 min in 0.01 mol L⁻¹ NaCl solution under 1.2 V, corresponding to a rapid average adsorption rate of 2 mg g⁻¹ min⁻¹. Moreover, the adsorption capacity could be further increased up to 121 and 136 mg g⁻¹ under 1.2 and 1.5 V for 2.5 h adsorption, respectively, but still far from its equilibrium value. Finally, experiments and theoretical simulations are combined to further understand the IDE in CDI. This work highlights the discovery and the utilization of IDE in CDI, and provides new guidance for the design of CDI electrodes and can facilitate the development of CDI technology.

电容去离子（CDI）是一种有效的微咸水淡化方法，以缓解全球淡水危机。获得高海水淡化能力是该领域的主要关注点。基于电极的电容和赝电容行为，目前的研究主要致力于增加电极材料的比表面积，然而，NaCl吸附容量通常限制在10-20 mg g ^{-1的范围内}. 在这项工作中，我们提出了一种新的设计范式，即为 CDI 使用垂直排列的纳米管结构。由于管内的水流大大减少，这种设计允许离子暂时保持在电极内，就像停靠在港口的船只（离子对接效应，IDE），从而提高了脱盐能力。结果，所获得的基于垂直排列的纳米管 P-TiO ₂阵列的 CDI 器件在 1.2 V 下，在 0.01 mol L ^{-1 NaCl 溶液中，在 30 分钟内表现出约 60 mg g -1}的超高 NaCl 吸附能力，对应于到2 mg g ^-1  min ^-1的快速平均吸附速率。此外，吸附容量可以进一步增加到 121 和 136 mg g ^-1分别在 1.2 和 1.5 V 下吸附 2.5 小时，但仍远离其平衡值。最后结合实验和理论模拟，进一步了解CDI中的IDE。该工作突出了IDE在CDI中的发现和利用，为CDI电极的设计提供了新的指导，可以促进CDI技术的发展。