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Results for “capacitive deionization”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

On the correlation between the porous structure and the electrochemical response of powdered and monolithic carbon aerogels as electrodes for capacitive deionization

The combined effect of resorcinol/catalyst (100≤R/C≤800) and resorcinol/water (0.04≤R/W≤0.13) molar ratio on the textural and capacitive properties of carbon aerogels with potential application for capacitive deionization has been evaluated. Activated and pyrolyzed aerogels were synthesized by the sol-gel polymerization of resorcinol-formaldehyde mixtures and dried in supercritical conditions. Data show that high R/C and R/W molar ratios lead to materials with large pores in the mesopore range, whereas the surface area and micropore volumes remain somewhat the same. The activation of the aerogels increased the differences in the specific surface and micropore volumes due to the development of microporosity. This effect was more remarkable for the samples with low R/C whatever the R/W ratio, indicating that the carbon aerogel obtained using high amounts of catalyst are more prone to be activated. Regarding the electrochemical features of the aerogels, low capacitance values were measured in aerogels combining low R/W and high R/C and reciprocally low R/C and high R/W molar ratios, due to their higher resistance. Polarization resistances were found to be slightly higher for the pyrolyzed than for activated aerogels, and followed a decreasing trend with the mesoporosity, indicating the outstanding contribution of the mesoporous network to provide a good kinetic response. The desalting capacity of monolithic aerogels showed a simultaneous dependence with the surface area and the resistivity of the electrodes, pointing out the importance of performing electrochemical measurements in adequate cell configurations (i.e., desalting units) upon the intended application. - Graphical abstract: The textural properties of carbon aerogels are strongly influenced by the synthesis parameters precursor to catalyst (R/C) and water (R/C) ratios. The volumetric capacitance measured in a symmetric cell with monolithic electrodes of carbon aerogel strongly correlates with both surface area and electrical resistivity. - Highlights: • Influence of the synthesis conditions on the properties of carbon aerogels is reported. • Specific surface decreases in the activated samples when either R/C or R/W increase. • An enhanced decrease of the capacitance was observed when R/C and R/W increase. • Ohmic resistance of the electrodes that strongly depends on the R/W and R/C. • Electrosorption capacity is successfully correlated to surface area and resistivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Modeling the Capacitive Deionization Process in Dual-Porosity Electrodes

In many areas of the world, there is a need to increase water availability. Capacitive deionization (CDI) is an electrochemical water treatment process that can be a viable alternative for treating water and for saving energy. A model is presented to simulate the CDI process in heterogeneous porous media comprising two different pore sizes. It is based on a theory for capacitive charging by ideally polarizable porous electrodes without Faradaic reactions or specific adsorption of ions. A two steps volume averaging technique is used to derive the averaged transport equations in the limit of thin electrical double layers. A one-equation model based on the principle of local equilibrium is derived. The constraints determining the range of application of the one-equation model are presented. The effective transport parameters for isotropic porous media are calculated solving the corresponding closure problems. The source terms that appear in the average equations are calculated using theoretical derivations. The global diffusivity is calculated by solving the closure problem.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2021

Nanoarchitectonics of Metal–Organic Frameworks for Capacitive Deionization via Controlled Pyrolyzed Approaches

Abstract Next‐generation desalination technologies are needed to meet the increasing demand for clean water. Capacitive deionization (CDI) is a thermodynamically efficient technique to treat non‐potable water with relatively low salinity. The salt removal capacity and rate of CDI are highly dependent on the electrode materials, which are preferentially porous to store ions through electrosorption and/or redox reactions. Metal–organic frameworks (MOFs) with “infinite” combinations of transition metals and organic linkers simplify the production of carbonaceous materials often with redox‐active components after pyrolysis. MOFs‐derived materials show great tunability in both compositions and structures but require further refinement to improve CDI performance. This review article summarizes recent progress in derivatives of MOFs and MOF‐like materials used as CDI electrodes, focusing on the structural and compositional material considerations as well as the processing parameters and electrode architectures of the device. Furthermore, the challenges and opportunities associated with this research area are also discussed.

Wang, Hao↗
DOE OSTI2015

Volume Averaging Study of the Capacitive Deionization Process in Homogeneous Porous Media

Ion storage in porous electrodes is important in applications such as energy storage by supercapacitors, water purification by capacitive deionization, extraction of energy from a salinity difference and heavy ion purification. In this paper, a model is presented to simulate the charge process in homogeneous porous media comprising big pores. It is based on a theory for capacitive charging by ideally polarizable porous electrodes without faradaic reactions or specific adsorption of ions. A volume averaging technique is used to derive the averaged transport equations in the limit of thin electrical double layers. Transport between the electrolyte solution and the charged wall is described using the Gouy–Chapman–Stern model. The effective transport parameters for isotropic porous media are calculated solving the corresponding closure problems. Finally, the source terms that appear in the average equations are calculated using numerical computations. An alternative way to deal with the source terms is proposed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Brackish water desalination using reverse osmosis and capacitive deionization at the water-energy nexus

Here, we present a critical review of the reported performance of reverse osmosis (RO) and capacitive deionization (CDI) for brackish water (salinity < 5.0 g/L) desalination from the aspects of engineering, energy, economy and environment. We first illustrate the criteria and the key performance indicators to evaluate the performance of brackish water desalination. We then systematically summarize technological information of RO and CDI, focusing on the effect of key parameters on desalination performance, as well as energy-water efficiency, economic costs and environmental impacts (including carbon footprint). We provide in-depth discussion on the interconnectivity between desalination and energy, and the trade-off between kinetics and energetics for RO and CDI as critical factors for comparison. We also critique the results of technical-economic assessment for RO and CDI plants in the context of large-scale deployment, with focus on lifetime-oriented consideration to total costs, balance between energy efficiency and clean water production, and pretreatment/post-treatment requirements. Finally, we illustrate the challenges and opportunities for future brackish water desalination, including hybridization for energy-efficient brackish water desalination, co-removal of specific components in brackish water, and sustainable brine management with innovative utilization. Our study reveals that both RO and CDI should play important roles in water reclamation and resource recovery from brackish water, especially for inland cities or rural regions.

42 ENGINEERING↗
DOE OSTI2023

Capacitive Deionization for the Extraction and Recovery of Butyrate

Separation processes underpin chemical manufacturing, energy and fuel production, resource recovery, and water purification. Capacitive deionization (CDI) is an electrochemical separation technique based on electrosorption of charged species from an aqueous solution. This work reports the development and application of CDI for the extraction and recovery of butyrate, a carboxylate anion that is key to bioenergy production, among other applications. Electrosorption of sodium butyrate was evaluated using a bench-scale CDI system with activated carbon cloth electrodes. Applying an external potential (1.2 V) enhanced the adsorption capacity of activated carbon for butyrate by 250%. Reversible electrosorption was also demonstrated by extracting and recovering butyrate at 1.2 and 0 V, respectively. Performance metrics including butyrate adsorption and desorption capacities, adsorption and desorption rates, charge efficiency, energy consumption, and recovery are reported. Furthermore, this study also investigates the long-term operational stability of the system by cycling the cell more than 1000 times using 1.2 and 0 V for charging and discharging, respectively. Subsequent physicochemical characterization indicates increased oxygen content (from similar to 2% to >8%), decreased specific surface area (by similar to 20%), and decreased pore volume (by similar to 20%), attributed to carbon oxidation. Overall, this work informs the design of CDI for organic anion separation and recovery.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Using Ultramicroporous Carbon for the Selective Removal of Nitrate with Capacitive Deionization

The contamination of water resources with nitrate is a growing and significant problem. Here we report the use of ultramicroporous carbon as a capacitive deionization (CDI) electrode for selectively removing nitrate from an anion mixture. Through moderate activation, we achieve a micropore-size distribution consisting almost exclusively of narrow (<1 nm) pores that are well suited for adsorbing the planar, weakly hydrated nitrate molecule. Cyclic voltammetry measurements reveal an enhanced capacitance for nitrate when compared to chloride as well as significant ion sieving effects when sulfate is the only anion present. We measure high selectivities ( S ) of both nitrate over sulfate ( S NO 3 /SO 4 = 17.8 ± 3.6 at 0.6 V) and nitrate over chloride ( S NO 3 /Cl = 6.1 ± 0.4 at 0.6 V) when performing a constant voltage CDI separation on 3.33 mM/3.33 mM/1.67 mM Cl/NO 3 /SO 4 feedwater. Furthermore, these results are particularly encouraging considering that a divalent interferant was present in the feed. Using molecular dynamics simulations, we examine the solvation characteristics of these ions to better understand why nitrate is preferentially electrosorbed over sulfate and chloride.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Two-Dimensional Porous Electrode Model for Capacitive Deionization

Here, ion transport in porous conductive materials is of great importance in a variety of electrochemical systems including batteries and supercapacitors. We here analyze the coupling of flow and charge transport and charge capacitance in capacitive deionization (CDI). In CDI, a pair of porous carbon electrodes is employed to electrostatically retain and remove ionic species from aqueous solutions. We here develop and solve a novel unsteady two-dimensional model for capturing the ion adsorption/desorption dynamics in a flow-between CDI system. We use this model to study the complex, nonlinear coupling between electromigration, diffusion, and advection of ions. We also fabricated a laboratory-scale CDI cell which we use to measure the near-equilibrium, cumulative adsorbed salt, and electric charge as a function of applied external voltage. We use these integral measures to validate and calibrate this model. We further present a detailed computational study of the spatiotemporal adsorption/desorption dynamics under constant voltage and constant flow conditions. We show results for low (20 mM KCl) and relatively high (200 mM KCl) inlet ion concentrations and identify effects of ion starvation on desalination. We show that in both cases electromigrative transport eventually becomes negligible and diffusive ion transport reduces the desalination rate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Bipolar Membrane Capacitive Deionization for the Selective Capture of Lithium Ions from Brines and Conversion to Lithium Hydroxide

Meeting the increasing demand for lithium in vehicle electrification and renewable energy storage requires innovations in lithium-ion (Li + ) separations. Traditional solar evaporation methods for lithium recovery are slow and consume tremendous volumes of water and secondary chemicals (acids and bases). This study introduces a bipolar membrane capacitive deionization (BPM-CDI) unit for direct lithium extraction and LiOH production without the external addition of acids and bases. Utilizing de-lithiated lithium-iron-phosphate (LFP) coated carbon cloth electrodes, the BPM-CDI unit demonstrates selective Li + capture over competing ions. Molecular dynamics simulations and H-cell experiments elucidate pH inversion mechanisms during Li + release, yielding LiOH. The BPM-CDI platform efficiently removes Li + from synthetic brines featuring 8x higher Mg 2+ concentrations (200 ppm Mg 2+ ) and 26x higher Na + concentrations (682 ppm Na + ), achieving a LiOH concentration of 124 ppm (36 ppm Li + ) after 8 cycles of recirculation. Post-mortem analysis confirms electrode integrity and stability. BPM-CDI integrated with selective electrodes is a promising electrochemical separation-reactor platform for lithium recovery while producing LiOH.

Kulkarni, Tanmay↗
DOE OSTI2016

Carbon electrode for desalination purpose in capacitive deionization

Carbon electrodes for desalination purpose have been successfully synthesized using activated carbon powder (BET surface area=700 – 1400 m{sup 2}/g), carbon black and polyvinyl alcohol (PVA) binder by cross-linking method with glutaric acid (GA) at 120 °C. The electrochemical properties of the carbon electrodes were analyzed using electrical impedance spectroscopy (EIS) and cyclic voltammetry (CV) whilst the physical properties were observed with scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX). In order to assess the desalting performance, salt removal experiments were performed by constructing a capacitive deionization unit cell with five pairs of carbon electrodes. For each pair consisted of two parallel carbon electrodes separated by a spacer. Desalination and regeneration processes were also observed in the salt-removal experiments. The salt-removal experiments were carried out in single-pass mode using a solution with 0.1 M NaCl at a flow rate of 10 mL/min. A voltage of 3 V was applied to the cell for 60 minutes for both processes in desalination and regeneration. The result showed that the percentage value of the salt-removal was achieved at 20%.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Energy consumption analysis of constant voltage and constant current operations in capacitive deionization

Here we report our studies to compare energy consumption of a CDI cell in constant voltage (CV) and constant current (CC) operations, with a focus on understanding the underlying physics of consumption patterns. The comparison is conducted under conditions that the CV and CC operations result in the same amounts of input charge and within identical charging phase durations. We present two electrical circuit models to simulate energy consumption in charging phase: one is a simple RC circuit model, and the other a transmission line circuit model. We built and tested a CDI cell to validate the transmission line model, and performed a series of experiments to compare CV versus CC operation under the condition of equal applied charge and charging duration. The experiments show that CC mode consumes energy at 33.8 kJ per mole of ions removed, which is only 28% of CV mode energy consumption (120.6 kJ/mol), but achieves similar level of salt removals. Lastly, together, the models and experiment support our major conclusion that CC is more energy efficient than CV for equal charge and charging duration. The models also suggest that the lower energy consumption of CC in charging is due to its lower resistive dissipation.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2015

Effect of oxidation of carbon material on suspension electrodes for flow electrode capacitive deionization

Flow electrode deionization (FCDI) is an emerging area for continuous and scalable deionization, but the electrochemical and flow properties of the flow electrode need to be improved to minimize energy consumption. We examine chemical oxidation of granular activated carbon (AC) here to study the role of surface heteroatoms on rheology and electrochemical performance of a flow electrode (carbon slurry) for deionization processes. Moreover, it was demonstrated that higher mass densities could be used without increasing energy for pumping when using oxidized active material. High mass-loaded flow electrodes (28% carbon content) based on oxidized AC displayed similar viscosities (~21 Pa s) to lower mass-loaded flow electrodes (20% carbon content) based on nonoxidized AC. The 40% increased mass loading (from 20% to 28%) resulted in a 25% increase in flow electrode gravimetric capacitance (from 65 to 83 F g –1 ) without sacrificing flowability (viscosity). The electrical energy required to remove ~18% of the ions (desalt) from of the feed solution was observed to be significantly dependent on the mass loading and decreased (~60%) from 92 ± 7 to 28 ± 2.7 J with increased mass densities from 5 to 23 wt %. Finally, it is shown that the surface chemistry of the active material in a flow electrode effects the electrical and pumping energy requirements of a FCDI system.

36 MATERIALS SCIENCE↗