Efficient Capacitive Deionization Using Thin Film Sodium Manganese Oxide
Journal Article
·
· Journal of the Electrochemical Society
Capacitive deionization (CDI) is an emerging electrochemical desalination technology, which could outperform other desalination technologies if new electrode materials are developed with high electrochemical salt sorption capacities. Recent work has demonstrated improved desalination efficiency using redox-active materials in hybrid CDI (hCDI) electrodes. Here, we report new charge-storage behavior in thin-film sodium manganese oxide (NMO) which promises to enable new levels of desalination efficiency. We deposit thin-film MnO via atomic layer deposition (ALD), and electrochemically convert it to NMO in NaCl(aq). NMO coated electrodes exhibit increases in charge storage capacity up to 170 times higher than uncoated electrodes. Electrochemical quartz crystal microbalance (EQCM) measurements reveal that thin-film NMO leads to the electrochemical removal of 2.3 Na+ ions per electron. This super-stoichiometric removal of Na+ is corroborated by ab initio modeling that predicts a new electrochemical phenomenon at the NMO surface, which we term electron-decoupled ion transfer, or “EDIT.” We also describe a new custom low-volume and low-mass-loading hCDI cell which enables the study of the desalination performance of the EDIT mechanism. An hCDI cell comprised of NMO-coated carbon nanotube (CNT) cathode and Ag nanoparticle-decorated CNT anode yields a ~20-fold improvement in charge storage over bare CNT electrodes. The hCDI cell has a reversible charging efficiency (mol NaCl (mol e-)-1) of 123 ± 5% and a coulombic efficiency of 93%, corroborating our EQCM results and the EDIT mechanism. The EDIT mechanism, as well as the hCDI cell design that enabled its study, promise to hasten the development of hCDI devices with unprecendented performance
- Research Organization:
- Argonne National Laboratory (ANL)
- Sponsoring Organization:
- USDOE Office of Science - Energy Frontier Research Center
- DOE Contract Number:
- AC02-06CH11357
- OSTI ID:
- 1466767
- Journal Information:
- Journal of the Electrochemical Society, Journal Name: Journal of the Electrochemical Society Journal Issue: 10 Vol. 165; ISSN 0013-4651
- Publisher:
- The Electrochemical Society
- Country of Publication:
- United States
- Language:
- English
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