WORCESTER BOSCH SET OF ELECTRODES 87186643010

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L. Eliad, G. Salitra, A. Soffer and D. Aurbach, J. Phys. Chem. B, 2001, 105, 6880–6887 CrossRef CAS. We introduce the volumetric partitioning function Φ exc, i = exp( μ exc, i,∞ − μ exc, i), and a similar term for affinity-based effects, Φ aff, i = exp( μ aff, i,∞ − μ aff, i), which lumps together all effects acting on the ion that are not ideal (entropy), volumetric, or charge-related. These factors Φ exc, i and Φ aff, i will be between 0 and 1 when such effects act to repel the ion from the micropore environment but will be >1 when they act to adsorb the ion into the micropore. We use Φ i = Φ exc, i· Φ aff, i. We obtain from eqn (3) a modified Boltzmann relation S. Kim, J. Lee, J. S. Kang, K. Jo, S. Kim, Y. E. Sung and J. Yoon, Chemosphere, 2015, 125, 50–56 CrossRef CAS. Adsorption and ion transport dynamics in intercalation materials. Theory for ion transport in CDI electrodes with ion mixtures has until now focused on electrodes based on porous carbons. Here, we extend the state-of-the-art and present the first model calculations for CDI with porous electrodes made from an intercalation material (such as NiHCF, a Prussian blue analogue). Our calculation results illustrate the general observation of ion selectivity studies that the ideal, or maximum attainable, or “thermodynamic”, separation factor (selectivity), is not easily reached in a practical process. This is because mass transfer limitations and mixing of ions lead to a lower selectivity value in the actual desalination process than the ideal value. This is also the case in the example calculation of CDI with intercalation materials presented below. Therefore, this example calculation serves to underscore the point that careful design of an electrochemical desalination cell and the operational conditions, thereby reducing transfer resistances and avoiding mixing, is crucial in increasing the actual selectivity to values as close as possible to the ideal, thermodynamic selectivity. K. Singh, Z. Qian, P. M. Biesheuvel, H. Zuilhof, S. Porada and L. C. P. M. de Smet, Desalination, 2020, 481, 114346 CrossRef CAS.

R. K. Kalluri, M. M. Biener, M. E. Suss, M. D. Merrill, M. Stadermann, J. G. Santiago, T. F. Baumann, J. Biener and A. Striolo, Phys. Chem. Chem. Phys., 2013, 15, 2320 RSC. In the limit of a relatively low concentration of ions in the pore ( η → 0) and small ion size ( α′ → 0), we arrive at μ exc, i = 8 γα′, and thus for the selectivity S between an ion 1 and ion 2 (ratio of ion concentrations in the pore, relative to that outside the pore) with different ion sizes d i we arrive at A recent study by Hawks et al. showed a high selectivity for nitrate over chloride and sulfate by using ultra-microporous (pore diameter < 1 nm) carbon electrodes. 41 The idea is similar to the one already explored by Eliad et al. (2001), in which selectivity is achieved due to sieving effect of very small carbon pores. The authors explored the effect of the solvation shell of the ion in aqueous media on their selective adsorption ( Fig. 6D). While chloride and sulfate ions are nearly homogeneously surrounded by water molecules, the solvation shell of a nitrate ion is mostly located at the edge of the ion and is not strongly bound to the molecule. As such, the authors suggested that the position of the solvation shell and the hydration energy instead of the average hydrated radius should be a more accurate parameter to be used in the investigation of ions selectivity based on ion size. The selectivity of nitrate over sulfate was also investigated. In this case, only a small amount of sulfate was electrosorbed inside the miniscule pores of the carbon electrode, which is explained by the higher solvation energy of sulfate compared to nitrate or chloride. In the electrosorption experiments, different cell potentials were applied to achieve the maximum selectivity ( ρ, Table 1) of NO 3 −/Cl − ≈ 6 and NO 3 −/SO 4 2− ≈ 18 at 0.6 V. At a cell voltage of 1.0 V, the NO 3 −/Cl − and NO 3 −/SO 4 2− selectivities were found to be ≈3 and ≈9, respectively. The observed reduction in selectivity with increasing cell voltage is explained by the solvation energy. At higher cell voltages, more energy is available to rearrange the solvation shell, and the ions be stored in the electrode. Consequently, the removal efficiencies of chloride and sulfate increase, reducing nitrate selectivity. In contrast, lower cell voltages limit the ion removal capacity due to co-ion repulsion, reducing the charge efficiency of the electrodes. Therefore, there is an optimum voltage that should be considered to maximize both energy efficiency and nitrate selectivity.

The effect of operational conditions on anion selectivity was explored in MCDI processes. Hassanvand et al. compared the electrosorption performance of MCDI with CDI using multicomponent solutions. 53 Compared to MCDI, CDI showed a lower nitrate removal than chloride, and a lower charge efficiency. Simultaneously, the presence of inverse peaks, which is caused by co-ion repulsion, was also observed during nitrate removal. Since nitrate has a high affinity to the carbon surface (both hydrophobic), nitrate accumulates on its surface being then repelled during the cathodic polarization, which was also reported by Mubita et al. The inversion peak disappeared by using an AEM, as already reported in literature, 7,135 and the removal of nitrate and chloride as well as their charge efficiencies became similar. At the same time, the removal of sulfate was lower than that of chloride and nitrate in CDI as well as MCDI. The use of an AEM resulted in a faster sulfate desorption even though the monovalent ions were preferred during the adsorption. A possible explanation of this observation provided by the authors is that a part of the sulfate ions were retained in the membrane surface, and therefore, the path length during the desorption was much shorter compared to that of monovalent ions. Akin to the work of Yeo et al., Zuo et al. investigated the viability of a resin to selectively remove sulfate from a mixture with chloride. 131 An experiment with the pristine high surface area carbon electrode demonstrated a higher selectivity towards chloride than sulfate ( S i/ j = 2.2), in agreement with the work of Sun et al. 75 The authors were able to reverse the selectivity (SO 4 2−/Cl − of 2.4) by coating the activated carbon electrode with the selective resin. The resin-coated carbon was able to maintain the selectivity of 1.9 towards sulfate even upon increasing the chloride concentration by a factor of 100. In contrast to some of the studies using nitrate-selective resins, 129,130 the authors did not report any issue during the desorption of the electrosorbed sulfate anions.

Mr Jayaruwan Gunathilake Gamaethiralalage is currently a PhD candidate in the Department of Organic Chemistry at Wageningen University & Research, The Netherlands. He received his BSc in chemistry from Kutztown University of Pennsylvania in the United States of America, joint MSc degrees in analytical chemistry from University of Tartu in Estonia, and Åbo Akademi University in Finland. His research interests include development of new material for ion separation and sensing, wastewater treatment, and electrodriven systems for circular water economy. The mD model was further improved by allowing the chemical potential term to vary with the micropore salt concentration, thereby eliminating the prediction of unrealistically large adsorption capacities at high salt concentrations. 14 It has also been extended from the one-dimensional case to cell-level, two-dimensional systems, 92 and has been corroborated by molecular dynamic simulations. 93 The mD model was applied to describe a series of CDI developments such as “inverted CDI” by fixing charge in the micropores to emulate chemical treatment, 15 inclusion of surface transport 94 and an explanation of the benefits of pulsed-flow CDI over continuous flow systems. 95 P. M. Biesheuvel, R. Zhao, S. Porada and A. van der Wal, J. Colloid Interface Sci., 2011, 360, 239–248 CrossRef CAS. c School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University, Daehak-dong, Gwanak-gu, Seoul 151-742, Republic of KoreaThe 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. Ratajczak, M. E. Suss, F. Kaasik and F. Béguin, Energy Storage Mater., 2019, 16, 126–145 CrossRef. B. Giera, N. Henson, E. M. Kober, M. S. Shell and T. M. Squires, Langmuir, 2015, 31, 3553–3562 CrossRef CAS. Dr Rafael Linzmeyer Zornitta is a postdoctoral researcher in the Organic Chemistry group at the Wageningen University & Research, The Netherlands. He received his BSc in Chemical Engineering from State University of Maringa (Brazil), MSc and PhD from Federal University of Sao Carlos (Brazil), with internships at the Malaga University (Spain), and Leibniz Institute for New Materials (Germany). His research interests include the development of new electrode materials, ion-selective membranes, and optimization of cell design for water desalination and selective ion recovery using electrochemical technologies.

Recently, Hu et al. proposed a new electrode based on layered metal oxide with Pd to remove nitrate using an approach similar to CDI. 113 However, the main difference was the reduction of NO 3 − to N 2 in the cathode of the cell by faradaic reactions. Although the authors did not provide a selectivity value, the electrodes are expected to exhibit high selectivity towards NO 3 − since its concentration in the electrode did not reach saturation. C. Erinmwingbovo, M. S. Palagonia, D. Brogioli and F. La Mantia, ChemPhysChem, 2017, 18, 917–925 CrossRef CAS. R. Chen, H. Tanaka, T. Kawamoto, M. Asai, C. Fukushima, H. Na, M. Kurihara, M. Watanabe, M. Arisaka and T. Nankawa, Electrochim. Acta, 2013, 87, 119–125 CrossRef CAS. On a system level, dependence of cell selectivity on operation parameters such as applied current, cell voltage, ion concentration, and pH among others will have to be systematically studied to find optimum conditions that enhance selectivity for the CDI cell. Intercalation electrodes such as TiS 2 show switchable preference depending on the potential of the electrode, as shown by Srimuk et al. 43 Such insights will be useful in realizing the full potential of existing (and the search for new) electrode materials.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. X. Zhang, K. Zuo, X. Zhang, C. Zhang and P. Liang, Environ. Sci.: Water Res. Technol., 2020, 6, 243–257 RSC.

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