Precisely Sized Channels in Novel Electrodes Enable Electrochemical Water Desalination
In electrochemical water desalination (or hybrid capacitative deionization), positive ions intercalate into the structure of the NWs, where they are trapped within precisely shaped/sized channels. An example of alpha-MnO2 NWs: (a) scanning electron microscopy image; (b) schematic of a single channel formed by MnO6 octahedra (red) with K+ (green), Na+ (blue), and Mg2+ (orange) ions; and (c) a Z-contrast STEM cross-section image of the NW channel structure. (hi-res image)
Manganese oxide nanowires (NWs) incorporating arrays of precisely shaped channels exhibit exceptional ion removal capabilities for brackish water desalination.
Significance and Impact
The unique crystal structures of MnO2 NWs contain stable channels with atomically defined sizes that preferentially trap specific ions from the salt solution. These materials will enable new deionization approaches.
– Ion removal occurs through surface redox reactions and intercalation of ions into the sub-nm-sized channels.
– Discrete MnO2 NW phases contain channels with different shapes and sizes, as measured by Z-contrast Scanning Transmission Electron Microscopy (STEM) imaging.
– Ion removal rates for Na, K, and Mg depend on the channel shape and size.
B. W. Byles, D. A. Cullen, K. L. More, and E. Pomerantseva, "Tunnel structured manganese oxide nanowires as redox active electrodes for hybrid capacitive deionization," Nano Energy44, 476-488 (2018). DOI: 10.1016/j.nanoen.2017.12.015