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Energy-efficient technologies for the remediation of water and generation of drinking water is a key towards sustainable technologies. Electrochemical desalination technologies are promising alternatives towards established methods, such as reverse osmosis or nanofiltration. In the last few years, hydrogen-driven electrochemical water purification has emerged. This review article explores the concept of desalination fuel cells and capacitive-Faradaic fuel cells for ion separation.
Capacitive deionization (CDI) is an emerging technology for the facile removal of charged ionic species from aqueous solutions, and is currently being widely explored for water desalination applications. The technology is based on ion electrosorption at the surface of a pair of electrically charged electrodes, commonly composed of highly porous carbon materials. The CDI community has grown exponentially over the past decade, driving tremendous advances via new cell architectures and system designs, the implementation of ion exchange membranes, and alternative concepts such as flowable carbon electrodes and hybrid systems employing a Faradaic (battery) electrode. Also, vast improvements have been made towards unraveling the complex processes inherent to interfacial electrochemistry, including the modelling of kinetic and equilibrium aspects of the desalination process. In our perspective, we critically review and evaluate the current state-of-the-art of CDI technology and provide definitions and performance metric nomenclature in an effort to unify the fast-growing CDI community. We also provide an outlook on the emerging trends in CDI and propose future research and development directions.
MXene as a novel intercalation-type pseudocapacitive cathode and anode for capacitive deionization
(2016)
In this proof-of-concept study, we introduce and demonstrate MXene as a novel type of intercalation electrode for desalination via capacitive deionization (CDI). Traditional CDI cells employ nanoporous carbon electrodes with significant pore volume to achieve a large desalination capacity via ion electrosorption. By contrast, MXene stores charge by ion intercalation between the sheets of its two-dimensional nanolamellar structure. By this virtue, it behaves as an ideal pseudocapacitor, that is, showing capacitive electric response while intercalating both anions and cations. We synthesized Ti3C2-MXene by the conventional process of etching ternary titanium aluminum carbide i.e., the MAX phase (Ti3AlC2) with hydrofluoric acid. The MXene material was cast directly onto the porous separator of the CDI cell without added binder, and exhibited very stable performance over 30 CDI cycles with an average salt adsorption capacity of 13 +/- 2 mg g-1.
Capacitive deionization (CDI) is an emerging technology for the energy-efficient removal of dissolved ions from aqueous solutions. Expanding this technology to non-aqueous media, we present an experimental characterization of a pair of porous carbon electrodes towards electrosorption of dissolved ions in propylene carbonate. We demonstrate that application of CDI technology for treatment of an organic solution with an electrochemical stability window beyond 1.2 V allows for a higher salt removal capacity and higher charge efficiency as compared to CDI applied for treatment of aqueous electrolytes. Further, we show that using conductivity measurements of the stream emerging from the CDI cell combined with an equilibrium electric double-layer structure model, we can gain insights into charge compensation mechanisms and ion distribution in carbon nanopores.
Main text: As population demands for freshwater increase, existing natural freshwater resources face significant strains. Currently, over 2.5 billion people live in localities that are subject to severe water scarcity at least 1 month of the year.1 Scarcity affects all types of localities, such as urban, rural, coastal areas, landlocked areas, and off-grid locations. Increasingly, active water purification technologies are being used to boost and secure freshwater supplies. A widely used desalination technology is seawater reverse osmosis (SWRO), in which pumps pressurize the feedwater to well above its osmotic pressure to pump water molecules through a membrane largely impermeable to salt ions (posmotic ∼ 25 bar).2 City-scale SWRO plants are operational in several countries, delivering on the order of 106 m3 of treated water per day (<0.1% of the total global daily water consumption). However, as the need for water purification increases and the requirements for each locality becomes more diverse, SWRO plants alone cannot meet the growing demand for a technological solution. Barriers toward increased penetration of SWRO include the enormous investment required to develop such plants, poor downscalability of the technology, the geographical limitation to coastal areas and near urban environments, and high energy requirements (typically about 4 kWh/m3).2 [...]
The demand for electronic devices that utilize lithium is steadily increasing in this rapidly advancing technological world. Obtaining high-purity lithium in an environmentally friendly way is challenging by using commercialized methods. Herein, we propose the first fuel cell system for continuous lithium-ion extraction using a lithium superionic conductor membrane and advanced electrode. The fuel cell system for extracting lithium-ion has demonstrated a twofold increase in the selectivity of Li+/Na+ while producing electricity. Our data show that the fuel cell with a titania-coated electrode achieves 95% lithium-ion purity while generating 10.23 Wh of energy per gram of lithium. Our investigation revealed that using atomic layer deposition improved the electrode's uniformity, stability, and electrocatalytic activity. After 2000 cycles determined by cyclic voltammetry, the electrode preserved its stability.