Tunnel structured manganese oxide nanowires as redox active electrodes for hybrid capacitive deionization
Tunnel structured manganese oxide nanowires as redox active electrodes for hybrid capacitive deionization
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DOI：
10.1016/j.nanoen.2017.12.015
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发表时间：
2018-02-01
期刊：
影响因子：
17.6
通讯作者：
Pomerantseva, Ekaterina
中科院分区：
文献类型：
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作者：
Byles, Bryan W.;Cullen, David A.;Pomerantseva, Ekaterina
混合电容去离子（HCDI）将电容性碳电极和氧化还原活性电极结合在一个设备中，已成为一种有前途的海水淡化方法，与包含两个碳电极的设备相比，其离子去除能力更高。然而，迄今为止，氧化还原活性材料的海水淡化性能报道还很少。我们首次展示了具有四种不同隧道晶体结构的氧化锰纳米线作为 HCDI 电池中法拉第电极的电化学行为。其中两个相是方形隧道结构的锰氧化物，α-MnO2 和钙锰矿-MnO2。另外两相具有新颖的结构，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。纳米线的离子去除性能不仅在实验室实验中传统使用的 NaCl 溶液中进行了评估，而且还在 KCl 和 MgCl2 溶液中进行了评估，从而更好地了解这些材料在含有多种阳离子的苦咸水淡化中的行为。高离子去除能力（在 NaCl、KCl 和 MgCl2 溶液中分别高达 27.8 mg g(-1)、44.4 mg g(-1) 和 43.1 mg g(-1)）和高离子去除率（高达 0.112 mg g(-1) s(-1)、0.165 mg g(-1) s(-1) 和 0.164 mg）分别在 NaCl、KCl 和 MgCl2 溶液中达到 g(-1) s(-1)。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，并且通过利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，氧化锰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，离子去除是通过表面氧化还原反应和离子嵌入结构通道来实现的。这项工作有助于理解法拉第材料在电化学水淡化中的行为，并阐明电极材料晶体结构与各种盐溶液中离子去除能力/离子去除率之间的关系。
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, alpha-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.