1:30 PM - *ES09.07.01
Ion Storage in Porous Electrodes—Can We Achieve and Describe Selective Ion Electrosorption?
Wetsus, European Centre of Excellence for Sustainable Water Technology1,University of Twente2
The continual increase in global population, along with a rapid progression towards extensive urbanization and industrialization, serves as the driving force for the upsurge in the development of water desalination technologies. There are only a limited number of ion removal technologies available on the market. Distillation is used for ion streams with high salt concentration, reverse osmosis (RO) is used for both intermediate salt concentrations as well as brackish water, and electrochemical technologies like electrodialysis (ED/EDR) and capacitive deionization (CDI) are used for brackish water with relatively low salt concentrations. In addition to desalination, there is an increasing demand for the selective uptake of ions. Along this line of motivation, CDI has the potential to offer diverse means to accomplish selective ion separation from aqueous solutions.
CDI is a water desalination technology that facilitates adsorption of ions via two oppositely polarized porous electrodes. In a traditional sense, CDI typically utilizes high surface area carbon materials, where the ions are trapped within the electrical double layers (EDLs) formed in the pores of the carbon electrodes . However, in recent times, new hybrid carbon-intercalation electrodes employing materials with redox activity have been introduced to CDI, [2, 3], in which the ionic species are stored in the crystallographic sites of the intercalation host compound (IHC).
Preferential ion electrosorption in capacitive deionization (CDI) has been the primary focal point of a number of contemporary studies. In general, the major influential factors that regulate ion selectivity of these porous electrodes include: (i) operating conditions such as applied cell voltage and initial ion concentration, (ii) ion properties like ion valence, hydrated size, and electronegativity, and (iii) micropore characteristics such as chemical surface groups and pore sizes. Hence, the technological hurdles associated with the development of efficient CDI electrodes with enhanced ion selectivity are manifold. Furthermore, a comprehensive knowledge of the underlying mechanisms and the materials involved is of prime importance to enact successful optimization of relevant process parameters (e.g. voltage, current, flow, cycle time), to attain preferable ion selectivity during the adsorption/regeneration phase.
This talk will be centered on the comparative analysis between conventional CDI electrodes with porous carbons, and the most recent intercalation electrodes [4, 5-6], utilized for the purpose of water desalination and selective ion separations. In the case of the latter, redox-active nickel hexacyanoferrate (NiHCF) nanoparticles embedded in a carbon matrix facilitates the intercalation and de-intercalation of Na+ ions, producing fresh water via a cyclic charging and discharging CDI process. Conclusively, alternate materials that can offer potential in advancing ion separation process will be also discussed.
This presentation provides a general overview addressing various material challenges in relation to ion removal within the domain of CDI.
1. M. E. Suss, et al. Energy. Environ. Sci., 2015, 8, 2296-2319.
2. M. Pasta, et al. Nano Lett., 2012, 12, 839-843.
3. P. Srimuk, et al. J. Mater. Chem. A, 2016, 4, 18265-18271.
4. K. C. Smith, J. Electrochem. Soc., 2016, 163, A530-A539.
5. S. Porada, et al. Electrochim. Acta, 2017, 255, 369-378.
6. K. Singh, at al. Phys. Rev. Appl., 2018, 9, 064036