Hybrid capacitive deionization (HCDI), which combines a capacitive carbon electrode and a redox active electrode in a single device, has emerged as a promising method for water desalination, enabling higher ion removal capacity than devices containing two carbon electrodes. However, to date, the desalination performance of few redox active materials has been reported. For the first time, we present the electrochemical behavior of manganese oxide nanowires with four different tunnel crystal structures as faradaic electrodes in HCDI cells. Two of these phases are square tunnel structured manganese oxides, α-MnO₂ and todorokite-MnO₂. The other two phases have novel structures that cross-sectional scanning transmission electron microscopy analysis revealed to have ordered and disordered combinations of structural tunnels with different dimensions. The ion removal performance of the nanowires was evaluated not only in NaCl solution, which is traditionally used in laboratory experiments, but also in KCl and MgCl₂ solutions, providing better understanding of the behavior of these materials for desalination of brackish water that contains multiple cation species. High ion removal capacities (as large as 27.8 mg g⁻¹, 44.4 mg g⁻¹, and 43.1 mg g⁻¹ in NaCl, KCl, and MgCl₂ solutions, respectively) and high ion removal rates (as large as 0.112 mg g⁻¹ s⁻¹, 0.165 mg g⁻¹ s⁻¹, and 0.164 mg g⁻¹ s⁻¹ in NaCl, KCl, and MgCl₂ solutions, respectively) were achieved. By comparing ion removal capacity to structural tunnel size, it was found that smaller tunnels do not favor the removal of cations with larger hydrated radii, and more efficient removal of larger hydrated cations can be achieved by utilizing manganese oxides with larger structural tunnels. Extended HCDI cycling and ex situ X-ray diffraction analysis revealed the excellent stability of the manganese oxide electrodes in repeated ion removal/ion release cycles, and compositional analysis of the electrodes indicated that ion removal is achieved through both surface redox reactions and intercalation of ions into the structural tunnels. This work contributes to the understanding of the behavior of faradaic materials in electrochemical water desalination and elucidates the relationship between the electrode material crystal structure and the ion removal capacity/ion removal rate in various salt solutions.

混合电容去离子（HCDI）在单个设备中结合了电容性碳电极和氧化还原活性电极，已成为一种有前景的水脱盐方法，与包含两个碳电极的设备相比，能够实现更高的离子去除能力。然而，迄今为止，已经报道了很少的氧化还原活性材料的脱盐性能。首次，我们介绍了具有四种不同隧道晶体结构的氧化锰纳米线作为HCDI电池中的法拉第电极的电化学行为。这些阶段中的两个平方隧道结构锰氧化物，α-MnO的₂和钙锰矿-的MnO ₂。其他两个阶段具有新颖的结构，其横截面扫描透射电子显微镜分析显示具有不同尺寸的结构隧道的有序和无序组合。不仅在传统上用于实验室实验的NaCl溶液中，而且还在KCl和MgCl ₂溶液中，对纳米线的离子去除性能进行了评估，从而更好地了解了这些材料对含多阳离子的微咸水进行脱盐的性能。物种。高的离子除去的能力（大至27.8毫克克^-1，44.4毫克克^-1和43.1毫克克^-1在NaCl，KCl和的MgCl ₂解决方案，分别地）和高的离子移除速率（大到0.112毫克克^-1小号^-1，0.165毫克克^-1小号^-1，和0.164毫克克^-1小号^-1在NaCl，KCl和的MgCl ₂解决方案）。通过将离子去除能力与结构隧道尺寸进行比较，发现较小的隧道不利于去除具有较大水合半径的阳离子，并且通过使用具有较大结构隧道的锰氧化物可以更有效地去除较大的水合阳离子。扩展的HCDI循环和异位X射线衍射分析表明，锰氧化物电极在重复的离子去除/离子释放循环中具有出色的稳定性，电极的成分分析表明，离子的去除是通过表面氧化还原反应和离子的嵌入实现的进入结构隧道。