Accurately measuring the ionic conductivity of membranes via the direct contact method

Díaz, José Carlos; Kitto, David; Kamcev, Jovan

doi:10.1016/j.memsci.2022.121304

Cited by 16 publications

(9 citation statements)

References 68 publications

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“…To better understand the role of CuHCF deposited at the CEM surface, the degree of ion transport under an electric field (i.e., electromigration) was quantified by EIS in the absence and presence of individual layers to isolate each contribution (Figure c; also see Figure S9 for representative Nyquist plots). The use of EIS allowed for extracting the membrane resistance from the overall membrane resistance involving the double layer and diffusional boundary layer. − The resistance of CuHCF-CEM was relatively low in NH 4 Cl (4.3 ± 0.3 Ω cm 2 ) compared to NaCl (5.7 ± 0.1 Ω cm 2 ). The CuHCF layer contributed less resistance to the overall membrane resistance in NH 4 + (1.2 ± 0.2 Ω cm 2 ) than in Na + (1.8 ± 0.1 Ω cm 2 ).…”

Section: Resultsmentioning

confidence: 99%

Selective Separation of Ammonium from Wastewater Using Ion Conducting Channels of a Prussian Blue Analogue

Chen,

Akinyemi,

Kim

2024

Environ. Sci. Technol. Lett.

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Wastewater treatment plants represent a centralized collection point of various resources, including ammonium, that could be recovered for the production of nitrogen fertilizer. Here, we show the use of copper hexacyanoferrates (CuHCFs) as ionconducting channels for the selective recovery of ammonium from wastewater. This model Prussian blue analogue was deposited at the surface of a cation exchange membrane (CEM) by a simple layer-by-layer precipitation method. The resulting CuHCF-CEM showed a selectivity of 5.0 ± 0.4 for NH 4 + relative to Na + using a binary mixture of synthetic wastewater (5 mM NH 4 Cl, 20 mM NaCl, 0.17 mA cm −2 ), which was nearly 5 times greater than the bare CEM. The improved selectivity was attributed to the CuHCF layer wherein NH 4 + could be migrated faster as well as more favorably occupied relative to Na + . The selectivity of CuHCF-CEM for NH 4 + was maintained relatively high compared with that of CEM in the presence of competing cations in a real domestic wastewater sample. This proof-of-concept study shows that selective ion-conducting channels of CuHCFs can provide a means to ammonia recovery from wastewater in electro-driven membrane processes.

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Section: Resultsmentioning

confidence: 99%

Selective Separation of Ammonium from Wastewater Using Ion Conducting Channels of a Prussian Blue Analogue

Chen,

Akinyemi,

Kim

2024

Environ. Sci. Technol. Lett.

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“…That is, potential complications of co-ions in the membrane, which are present when the membrane is equilibrated with an electrolyte solution, are eliminated. Furthermore, by establishing direct contact between the membrane and electrodes, effects associated with ion partitioning at the membrane-solution interface are removed, provided that interfacial resistances between the membrane and electrodes are properly accounted for . That is, experiments performed with the direct contact method directly probe ion migration within the membrane.…”

Section: Resultsmentioning

confidence: 99%

“…The ionic conductivity of DI water-equilibrated membranes was measured via electrochemical impedance spectroscopy using the “direct contact” method. , In this method, the membrane is compressed between two electrodes during the measurements. The direct contact method has several advantages over the alternative method that implements an electrolyte solution between the membrane and electrodes (i.e., “difference” method).…”

Section: Resultsmentioning

confidence: 99%

Understanding Monovalent Cation Diffusion in Negatively Charged Membranes and the Role of Membrane Water Content

Díaz,

Park,

Shapiro

et al. 2024

Macromolecules

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Membranes capable of differentiating between similarly charged ions could enable applications such as resource recovery from naturally occurring waters and industrial wastewaters. Understanding the factors that govern ion transport in these materials is crucial for designing such membranes. This study investigates the impact of membrane water content on the diffusion of monovalent cations in negatively charged membranes by using absolute reaction rate theory. The ion activation energy and entropy of diffusion in the membrane both increase substantially when most of the water is structurally bound. The increase in activation energy of diffusion is predicted by a model incorporating Coulombic interactions between the membrane fixed charges and counterions. The activation entropy of diffusion in the low water content membranes increases with increasing size of the hydrated cations, suggesting possible rearrangement in the primary hydration shells of strongly hydrated cations, such as Li + and Na + , during diffusion. These results suggest that polymer tortuosity, Coulombic interactions, and water structure govern monovalent cation diffusion in negatively charged membranes.

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“…Potentiostatic EIS was used to determine the ionic conductivity of the CEM. − For the virgin CEM and each used CEM, four samples were cut slightly larger than the circular electrode (2 cm diameter) in the sample holder and equilibrated with 0.1 M NaCl solution overnight prior to measurement. Stacks consisting of 1, 2, and 3 samples were placed into a sample holder (BioLogic CESH-e, Seyssinet-Pariset, France) and compressed to allow through-plane measurement.…”

Section: Methodsmentioning

confidence: 99%

Long-Term Robustness and Failure Mechanisms of Electrochemical Stripping for Wastewater Ammonia Recovery

Kogler,

Sharma,

Tiburcio

et al. 2024

ACS Environ. Au

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Nitrogen in wastewater has negative environmental, human health, and economic impacts but can be recovered to reduce the costs and environmental impacts of wastewater treatment and chemical production. To recover ammonia/ ammonium (total ammonia nitrogen, TAN) from urine, we operated electrochemical stripping (ECS) for over a month, achieving 83.4 ± 1.5% TAN removal and 73.0 ± 2.9% TAN recovery. With two reactors, we recovered sixteen 500-mL batches (8 L total) of ammonium sulfate (20.9 g/L TAN) approaching commercial fertilizer concentrations (28.4 g/L TAN) and often having >95% purity. While evaluating the operation and maintenance needs, we identified pH, full-cell voltage, product volume, and water flux into the product as informative process monitoring parameters that can be inexpensively and rapidly measured. Characterization of fouled cation exchange and omniphobic membranes informs cleaning and reactor modifications to reduce fouling with organics and calcium/magnesium salts. To evaluate the impact of urine collection and storage on ECS, we conducted experiments with urine at different levels of dilution with flush water, extents of divalent cation precipitation, and degrees of hydrolysis. ECS effectively treated urine under all conditions, but minimizing flush water and ensuring storage until complete hydrolysis would enable energy-efficient TAN recovery. Our experimental results and cost analysis motivate a multifaceted approach to improving ECS's technical and economic viability by extending component lifetimes, decreasing component costs, and reducing energy consumption through material, reactor, and process engineering. In summary, we demonstrated urine treatment as a foothold for electrochemical nutrient recovery from wastewater while supporting the applicability of ECS to seven other wastewaters with widely varying characteristics. Our findings will facilitate the scale-up and deployment of electrochemical nutrient recovery technologies, enabling a circular nitrogen economy that fosters sanitation provision, efficient chemical production, and water resource protection.

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Accurately measuring the ionic conductivity of membranes via the direct contact method

Cited by 16 publications

References 68 publications

Selective Separation of Ammonium from Wastewater Using Ion Conducting Channels of a Prussian Blue Analogue

Selective Separation of Ammonium from Wastewater Using Ion Conducting Channels of a Prussian Blue Analogue

Understanding Monovalent Cation Diffusion in Negatively Charged Membranes and the Role of Membrane Water Content

Long-Term Robustness and Failure Mechanisms of Electrochemical Stripping for Wastewater Ammonia Recovery

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