WORCESTER BOSCH SET OF ELECTRODES 87186643010

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For the case where all ions are monovalent, or all ions are divalent, the resulting equation for σ 0 versus ϕ D has been often presented, see ref. 156.

Introduction Fresh water scarcity and rapidly increasing global demand for clean water have stimulated scientists to seek out innovative methods of securing potable water supplies. Even though water desalination is deeply rooted within the human history, spanning across centuries, 1 it was not until the latter half of 20th century that desalination techniques became commercialized. 2 Conventional desalination methods, such as reverse osmosis (RO), electrodialysis (ED), multi-stage-flash (MSF), and multi-effect desalination (MED), are commonly used, but in some cases require significant energy input to produce fresh water. Furthermore, the majority of these systems often desalinate ‘to completion’, or do not preferentially remove the ions that are desired to be removed or even harvested. Ion selectivity is of key importance because it is often not necessary, and perhaps even detrimental, to remove the vast majority or entirety of ions from water. There are ample examples where one specific ion is to be removed because of its toxicity (arsenic, boron, heavy metals, ions leading to fouling, and sodium in irrigation water) or value (lithium, gold). In this review we focus on the ion selectivity ( i.e. preferential removal of a particular ion of interest within a mixture of ions) aspect of water desalination via capacitive deionization (CDI). The promising results of this seminal study have motivated further research of intercalation materials for desalination batteries, focused mainly on development of high capacity Na-insertion electrodes and alternatives for the Ag electrode. A potential alternative to Ag electrodes for Cl − storage, bismuth electrodes exploit the conversion of Bi to BiOCl. 123 The primary motivation for this alternative is its lower cost. 134,135 Unfortunately, Bi electrodes suffer from both H + production during oxidation of Bi to BiOCl, which lowers the solution pH, and slow kinetics of the reduction reaction in non-acidic conditions. The Na + removal was performed with a NASICON-type NaTi 2(PO 4) 3 electrode due to its high theoretical capacity. This electrode paring with Bi removes 3 Na + for every Cl −, which decreases the pH. Due to the imbalance of the ion removal and the decreasing pH, the NaTi 2(PO 4 P. M. Biesheuvel, S. Porada, M. Levi and M. Z. Bazant, J. Solid State Electrochem., 2014, 18, 1365–1376 CrossRef CAS. S. Mao, L. Chen, Y. Zhang, Z. Li, Z. Ni, Z. Sun and R. Zhao, J. Colloid Interface Sci., 2019, 544, 321–328 CrossRef CAS.Activated carbon. Activated carbon, defined by its high surface area to volume ratio, was used in the first CDI system 16 developed in the 1960's; in recent years this material has been modified to achieve even higher surface areas and hierarchical pore geometries with fast charge transfer and ion diffusion kinetics. In general, activated carbon, comprised of aggregates of microporous particles, is fabricated through pyrolysis of a carbon precursor, such as wood, then is activated ( i.e. micropores are created) via chemical etching or gasification of the product. 45 Although the typical performance of activated carbon electrodes does not match those of 1D and 2D materials (see Fig. 8a for a comparison), the low cost of activated carbon makes it an appealing electrode material for commercial applications. 47,48 Flow-electrode CDI. In a recent addition to the set of CDI systems, flow-electrode capacitive deionization (FCDI) was invented to solve the persistent issue of the finite adsorption capacity of standard CDI cell designs. 81 In FCDI, a carbon slurry flows through channels between the current collector and IEM, continuously replenishing the capacitive material and eliminating the need for the regeneration step that pauses desalination ( Fig. 3b). Various closed-systems, in which the slurry is continuously discharged and re-used without pausing the desalting step, have been demonstrated. 82,83 Because the electrode material is continuously regenerated at a rate set by the electrode flow speed, performance metrics such as electrode capacity become less important; the limiting factor for FCDI, as shown in recent studies, is instead electrode conductivity. Y. Gao, L. Pan, H. B. Li, Y. Zhang, Z. Zhang, Y. Chen and Z. Sun, Thin Solid Films, 2009, 517, 1616–1619 CrossRef CAS.

Ren et al. employed a flow MCDI (FCDI) cell to remove phosphate and ammonium from an aqueous solution. 133 Although it was found to be possible to remove large amounts of phosphate, the selectivity using this cell design was not explored. Further insight about selectivity using FCDI was reported by Bian et al. who studied the best operational conditions for the removal of phosphate and nitrate. 134 They observed a strong increase in the phosphate removal by increasing the carbon loading of the anode. This increase was steeper than that for nitrate (and ammonia), and was ascribed to the physical adsorption of phosphate in addition to electrosorption ( Fig. 6E), similar to the results obtained by Ge et al. On the other hand, for low carbon loadings, FCDI was found to be much more selective towards nitrate (1.1 at 15 wt% carbon loading to 1.7 at 5 wt%). L. Eliad, G. Salitra, A. Soffer and D. Aurbach, J. Phys. Chem. B, 2001, 105, 6880–6887 CrossRef CAS. which is set up and solved at each coordinate twice, first for i = Na + with j = K + and second for the reverse situation. In this equation, parameter V T is the thermal voltage given by V T = RT/ F which at room temperature is around 25.6 mV. All other parameter values are given in ESI (Section 7) of Porada et al. 78 Z. Sun, L. Chai, M. Liu, Y. Shu, Q. Li, Y. Wang and D. Qiu, Chemosphere, 2018, 195, 282–290 CrossRef CAS. C. Erinmwingbovo, M. S. Palagonia, D. Brogioli and F. La Mantia, ChemPhysChem, 2017, 18, 917–925 CrossRef CAS.

c i,in and c i,f are initial and final concentrations of the target ion. c j,in and c j,f are initial and final concentrations of the competing ion. K. Singh, S. Porada, H. D. de Gier, P. M. Biesheuvel and L. C. P. M. de Smet, Desalination, 2019, 455, 115–134 CrossRef CAS.

C. D. Wessells, S. V. Peddada, M. T. McDowell, R. A. Huggins and Y. Cui, J. Electrochem. Soc., 2011, 159, A98–A103 CrossRef.

D. I. Oyarzun, A. Hemmatifar, J. W. Palko, M. Stadermann and J. G. Santiago, Water Res.: X, 2018, 1, 100008 Search PubMed. where η′ is a modified volume fraction of ions in the pore, which is the real volume fraction η, to which is added an empirical term γα′ which relates to the ion size to pore size ratio. The volume fraction η is given by a summation over all ions in the pore of their concentration in the micropores times the molar volume, i.e., the volume (per mole of ions), which can include the water molecules that are tightly bound to the ion (ion plus hydration shell). For larger ions, the γα′ term is larger, and thus for this ion, Φ exc, i will be lower and it will be excluded from the pores relative to the smaller ion. Though this function is derived from a Carnahan–Starling equation of state, which considers mixtures of ions of the same size, 160 we utilize this simplified expression here to describe a size-based selectivity in mixtures of ions of different sizes. S. J. Seo, H. Jeon, J. K. Lee, G. Y. Kim, D. Park, H. Nojima, J. Lee and S. H. Moon, Water Res., 2010, 44, 2267–2275 CrossRef CAS. J. Kim, A. Jain, K. Zuo, R. Verduzco, S. Walker, M. Elimelech, Z. Zhang, X. Zhang and Q. Li, Water Res., 2019, 160, 445–453 CrossRef CAS.