| 1. |
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| 2. |
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| 3. |
- Foloppe, N, et al.
(författare)
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Structure, dynamics and electrostatics of the active site of glutaredoxin 3 from Escherichia coli : Comparison with functionally related proteins
- 2001
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Ingår i: Journal of Molecular Biology. - : Elsevier BV. - 0022-2836 .- 1089-8638. ; 310:2, s. 449-470
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Tidskriftsartikel (refereegranskat)abstract
- The chemistry of active-site cysteine residues is central to the activity of thiol-disulfide oxidoreductases of the thioredoxin superfamily. In these reactions, a nucleophilic thiolate is required, but the associated pK(a), values differ vastly in the superfamily, from less than 4 in DsbA to greater than 7 in Trx. The factors that stabilize this thiolate are, however, not clearly established. The glutaredoxins (Grxs), which are members of this superfamily, contain a Cys-Pro-Tyr-Cys motif in their active site. In reduced Grxs, the pK(a) of the N-terminal active-site nucleophilic cysteine residue is lowered significantly, and the stabilization of the corresponding thiolate is expected to influence the redox potential of these enzymes. Here, we use a combination of long molecular dynamics (MD) simulations, pK(a) calculations, and experimental investigations to derive the structure and dynamics of the reduced active site from Escherichia coli Grx3, and investigate the factors that stabilize the thiolate. Several different MD simulations converged toward a consensus conformation for the active-site cysteine residues (Cys11 and Cys14), after a number of local conformational changes. Key features of the model were tested experimentally by measurement of NMR scalar coupling constants, and determination of pK(a) values of selected residues. The pK(a) values of the Grx3 active-site residues were calculated during the MD simulations, and support the underlying structural model. The structure of Grx3, in combination with the pK(a) calculations, indicate that the pK(a) of the N-terminal active-site cysteine residue in Grx3 is intermediate between that of its counterpart in DsbA and Trx. The pK(a) values in best agreement with experiment are obtained with a low (<4) protein dielectric constant. The calculated pK(a) values fluctuate significantly in response to protein dynamics, which underscores the importance of the details of the underlying structures when calculating pK(a) values. The thiolate of Cys11 is stabilized primarily by direct hydrogen bonding with the amide protons of Tyr13 and Cys14 and the thiol proton of Cys14, rather than by long range interactions from charged groups or from a helix macrodipole. From the comparison of reduced Grx3 with other members of the thioredoxin superfamily, a unifying theme for the structural basis of thiol pK(a) differences in this superfamily begins to emerge.
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| 4. |
- Hadidi, Hooman, et al.
(författare)
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Numerical investigation of capacitive deionization (CDI) with divergent and convergent channels
- 2023
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 944
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Tidskriftsartikel (refereegranskat)abstract
- This research aims to explore the impact of tilted channel configurations of CDI cells on desalination performance. The results reveal that the titled convergent channels have a faster average salt adsorption rate (ASAR) than the regular straight geometry. For desalination operations that end at a quarter of the equilibrium salt adsorption capacity (SAC), the convergent spacer with a slight slope of 1.5 degrees has a 20 % higher ASAR than the typical straight geometry (0.15 mg/g/min for convergent and 0.12 mg/g/min for straight). This gain increases to about 24, 29.5, and 33%, respectively, for slopes of 3.5, 5.5, and 7 degrees, compared to the straight geometry with the same spacer thickness. By looking at the underlying mechanisms, the spacer geometry is found to shift the location of the initial adsorption. This affects how quickly the device outputs the cleaned water. Interestingly, the geometry angle can also affect the location of the depletion zone, so tilted spacers can also affect the behavior during electrode starvation. Specifically, the convergent geometry has the depletion zone in the middle of the electrode instead of the corner near the outlet, as seen for straight and divergent channels. Together, these findings indicate how to construct tilted spacers to enhance CDI performance.
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| 5. |
- Nilsson, Jonas, et al.
(författare)
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Prostate cancer-derived urine exosomes : a novel approach to biomarkers for prostate cancer.
- 2009
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Ingår i: British journal of cancer. - : Springer Science and Business Media LLC. - 1532-1827 .- 0007-0920. ; 100:10, s. 1603-1607
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we describe a novel approach in the search for prostate cancer biomarkers, which relies on the transcriptome within tumour exosomes. As a proof-of-concept, we show the presence of two known prostate cancer biomarkers, PCA-3 and TMPRSS2:ERG the in exosomes isolated from urine of patients, showing the potential for diagnosis and monitoring cancer patients status.
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| 6. |
- Nordstrand, Johan, et al.
(författare)
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2D Simulations of Water Treatment with Upscaled Capacitive Deionization
- 2022
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Ingår i: Proceedings of the 10th International Workshop on Simulation for Energy, Sustainable Development & Environment (SESDE), 00419th International Multidisciplinary Modeling & Simulation Multiconference. - : Cal-Tek Srl.
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Konferensbidrag (refereegranskat)abstract
- Clean water is a major global challenge. Meanwhile, capacitive deionization (CDI) is an emerging desalination technology that could help produce and reuse water. As the technology develops, the modeling of upscaled systems is becoming increasingly relevant. However, the inherent complexities in the CDI process have historically made such simulations unfeasible. In this work, we leverage the newly published electrolytic-capacitor (ECL) model to efficiently simulate parallel/serial flow modes in CDI stacks. The simulations are based on finite-element methods (FEM) that couple differential equations for describing local charging and ionic transport inside the device. The results show that both parallel and serial connections scale incredibly well with the system size. Still, parallel connections have the advantage of requiring lower pumping energy. Overall, we find that the relationship between adsorption capacity, flowrate, and compartment size is a good indicator of performance. In conclusion, the ELC model is promising for simulating upscaled CDI.
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| 7. |
- Nordstrand, Johan, et al.
(författare)
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A new automated model brings stability to finite‐element simulations of capacitive deionization
- 2022
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Ingår i: Nano Select. - : Wiley. - 2688-4011. ; 3:6, s. 1021-1035
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Tidskriftsartikel (refereegranskat)abstract
- The massive need for freshwater is driving new desalination technologies such as capacitive deionization (CDI), wherein an applied electric field between porous electrodes removes salt ions from water. In this work, we present substantial advances in numerical approaches to 2D finite-element models that make it possible to tractably and accurately simulate the local transport, charge-transfer, and ion-adsorption processes. This is achieved by introducing a new numerical approach that improves the stability of the method (SmD), which further allows precise and effective modeling that was previously too unstable for use in the state-of-the-art 2D models. The results show that the model now accurately and reliably simulates CDI processes while being effectively applicable to a wider range of structural (device level) and operational conditions (like flow). Crucially, this opens up new opportunities that allow us to provide novel insights into the CDI processes, especially relating to ion-starved conditions. Finally, novel algorithms support fully automatic implementation with simultaneous fit to multiple data sets and we openly provide all software code to increase accessibility. Thus, we fundamentally believe that the developed model will provide a solid foundation for 2D spatiotemporal simulations of capacitive deionization and aid the future development of CDI technology.
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| 8. |
- Nordstrand, Johan, et al.
(författare)
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An Easy-to-Use Tool for Modeling the Dynamics of Capacitive Deionization
- 2019
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 123:30, s. 6628-6634
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Tidskriftsartikel (refereegranskat)abstract
- Capacitive deionization is an emerging method of desalinating brackish water that has been presented as an alternative to the widely applied technologies such as reverse osmosis. However, for the technology to find more widespread use, it is important not only to improve its efficiency but also to make its modeling more accessible for researchers. In this work, a program has been developed and provided as an open-source with which a user can simulate the performance of a capacitive deionization system by simply entering the basic experimental conditions. The usefulness of this program was demonstrated by predicting how the effluent concentration in a continuous-mode constant-voltage operation varies with time, as well as how it depends on the flow rate, applied voltage, and inlet ion concentration. Finally, the generality of the program has been demonstrated using data from reports in the literature wherein various electrode materials, cell structures, and operational modes were used. Thus, we conclude that the model, termed the dynamic Langmuir model, could be an effective and simple tool for modeling the dynamics of capacitive deionization.
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| 9. |
- Nordstrand, Johan, et al.
(författare)
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An Extended Randles Circuit and a Systematic Model-Development Approach for Capacitive Deionization
- 2021
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 168:1
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Tidskriftsartikel (refereegranskat)abstract
- The global need for freshwater rapidly drives the development of emerging and efficient freshwater-production methods such as capacitive deionization (CDI). To allow the CDI technique to continue to grow, simulations can be important for tractably describing, predicting, and optimizing the desalination processes. Amongst the disparate simulation tools available, the Randles-circuit model is widely used in electrochemical measurements but its simplified structure limits its use for wider CDI operations. Thus, we herein describe a systematic stepwise process for widely developing CDI models, and as a proof-of-concept, transform the core Randles circuit into an extended Randles circuit (ERaC) that is highly relevant for CDI systems. Experimental data from the literature extensively verify that the ERaC model accuracy now describes charge storage, charging rate, ion adsorption, and current leakages for a variety of structural and operational parameters, such as asymmetric electrodes, different ion concentrations, and the applied voltage. In conclusion, this developed stepwise process can systematically and effectively create, enhance, and expand CDI models. Thus, researchers will embrace this method of model development, and benefit from the broad usefulness of the proposed ERaC model for a wide range of CDI operations.
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| 10. |
- Nordstrand, Johan
(författare)
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At the Mountains of Modeling : Multiscale Simulations of Desalination by Capacitive Deionization
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- More than 2 billion people are living in water-scarce areas. Meanwhile, there are enormous amounts of water in the salty oceans. Capacitive deionization (CDI) rises to the challenge with electrochemical cells for desalinating the water. As the CDI field expands, modeling becomes an increasingly important part of the development landscape. Multiscale modeling could bring innovations from the material scale to pilot plants. The multiscale work in this thesis has been like climbing a mountain. At the start, we investigate the macroscopic device level. One milestone is the electrolytic-capacitor (ELC) model, which can simulate CDI process dynamics. Whereas previous 2D models were unsteady for a single CDIcell, the ELC model could accurately simulate stacks of over 100 cells at a fraction of the time. It also enables simulations of complex upscaled geometries, such as bipolar electrode stacks, ohmic charging, and asymmetric devices. Going up the mountain, the mesoscopic level reveals the local mechanisms behind the macroscopic behavior. One important stepping stone is the dynamic Langmuir (DL) model, which reveals how isotherm-based modeling can crease stable and tractable simulations. Also, developments in isotherm, double-layer, and circuit modeling make it possible to choose what model structures to lean on depending on the conditions. Near the top of the mountain, the microscopic level shows the fundamental atomic mechanisms behind the mesoscopic material properties. These investigations reveal a ladder mechanism of ion transport in crystals of Prussian blue analogs (PBA), meaning the cations climb frames formed by negative groups in the crystal structure.In the end, we plant a flag by combining the developments from the journey into a complete multiscale model. That model demonstrated that we could predict CDI charging trends from the atomic structure of PBA electrodes. Having the full multiscale model also made it possible to backtrack and determine atomic-level mechanisms by comparing the output of different mechanism cases with macroscopic experiment data. The multiscale mountain is massive and has big potential. A dream is that future research will expand these concepts, in CDI and beyond.
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| 11. |
- Nordstrand, Johan, et al.
(författare)
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Basis and Prospects of Combining Electroadsorption Modeling Approaches for Capacitive Deionization
- 2020
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Ingår i: Physics. - : Multidisciplinary Digital Publishing Institute. - 2624-8174. ; 2:2, s. 309-324
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Tidskriftsartikel (refereegranskat)abstract
- Electrically driven adsorption, electroadsorption, is at the core of technologies for water desalination, energy production, and energy storage using electrolytic capacitors. Modeling can be crucial for understanding and optimizing these devices, and hence different approaches have been taken to develop multiple models, which have been applied to explain capacitive deionization (CDI) device performances for water desalination. Herein, we first discuss the underlying physics of electroadsorption and explain the fundamental similarities between the suggested models. Three CDI models, namely, the more widely used modified Donnan (mD) model, the Randles circuit model, and the recently proposed dynamic Langmuir (DL) model, are compared in terms of modeling approaches. Crucially, the common physical foundation of the models allows them to be improved by incorporating elements and simulation tools from the other models. As a proof of concept, the performance of the Randles circuit is significantly improved by incorporating a modeling element from the mD model and an implementation tool from the DL model (charge-dependent capacitance and system identification, respectively). These principles are accurately validated using data from reports in the literature showing significant prospects in combining modeling elements and tools to properly describe the results obtained in these experiments
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| 12. |
- Nordstrand, Johan, et al.
(författare)
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Design principles for enhanced up-scaling of flow-through capacitive deionization for water desalination
- 2020
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Ingår i: Desalination. - : Elsevier. - 0011-9164.
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Tidskriftsartikel (refereegranskat)abstract
- To develop efficient and cost-effective desalination technologies is crucial for addressing the globally increasing needs for drinking water. One such desalination technology that is growing is capacitive deionization (CDI), wherein ions are electrically removed from water passing through or between two porous conducting electrodes. As the CDI field grows, design principles for scaling from small CDI cells to larger units and modules will become increasingly important. Thus, we have investigated the flow distribution in single flow-through CDI cells and interconnected modules to determine architectural principles that can feasibly reduce the pressure drop with good throughput, thus increasing energy efficiency. The most important principles found include massive parallelism, open regions to symmetrically distribute flow, and tailoring the permeability of the electrodes and spacers. Crucially, we demonstrate how simply rerouting the flow reduces the pressure drop through the cell by a factor of four in a two-cell system. Finally, we leverage the found principles to a cylindrical CDI cell well-adapted to modular up-scaling. In conclusion, implementing the design principles leads to a significant reduction in pressure drop and energy consumption of a CDI system, which is essential for upscaling to larger modular systems for practical use.
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| 13. |
- Nordstrand, Johan, et al.
(författare)
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Dynamic Langmuir Model : A Simpler Approach to Modeling Capacitive Deionization
- 2019
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:26, s. 16479-16485
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Tidskriftsartikel (refereegranskat)abstract
- Capacitive deionization (CDI) is emerging as an environment-friendly and energy-efficient water desalination option for meeting the growing global demand for drinking water. It is important to develop models that can predict and optimize the performance of CDI systems with respect to key operational parameters in a simple way. Such models could open up modeling studies to a wider audience by making modeling more accessible to researchers. We have developed the dynamic Langmuir model that can describe CDI in terms of a few fundamental macroscopic properties. Through extensive comparisons with data from the literature, it is shown that the model could describe and predict charge storage, ion adsorption, and charge efficiency for varying input ion concentrations, applied voltages, electrolyte compositions, electrode asymmetries, and electrode precharges in the equilibrium state. We conclude that the model could accurately describe a wide range of key features while being a simpler approach than the commonly applied theories for modeling CDI.
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| 14. |
- Nordstrand, Johan, et al.
(författare)
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ELC: Software and tutorial for finite-element modeling of electrochemical desalination
- 2022
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Ingår i: SoftwareX. - : Elsevier BV. - 2352-7110. ; 20
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Tidskriftsartikel (refereegranskat)abstract
- Many works in capacitive deionization (CDI) use finite-element (FEM) simulations to investigate process behavior. Here, we present ELC, comprehensive software that integrates these methods with COMSOL Multiphysics. It can save significant time for common research questions in CDI operations and is well-suited for new research questions in complex and upscaled device designs. The ELC software has already been used for the simulation of time-varying desalination output, charge leakages, bipolar electrode devices, and stacks of over 100 CDI cells. Finally, we provide a video tutorial on how to use the software. In conclusion, ELC could be a strong software for aiding current and future research in electrochemical desalination.
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| 15. |
- Nordstrand, Johan, et al.
(författare)
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Electrostatic interactions and physisorption: mechanisms of passive cesium adsorption on Prussian blue
- 2022
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:41, s. 25452-25461
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Tidskriftsartikel (refereegranskat)abstract
- The dangers posed by nuclear accidents necessitate developments in techniques for cesium removal. One such is the adsorption of cesium cations in Prussian blue (PB) materials, on which adsorption can be a substation process or pure physisorption. The underlying mechanism of the latter is not well understood, although a Langmuir isotherm is frequently used to model experimental results. In this work, we exploit tight-binding density-functional theory (DFTB) methods to probe the atomic interactions in the physisorption process. The results show that there is a diminishing return for the energy of adsorption as more sites are filled. This means that the adsorption sites are not independent, as stipulated by the ideal Langmuir isotherm. Instead, the results indicate that electrostatic effects need to be considered to explain the theoretical and experimental results. Therefore, an electrostatic Langmuir (EL) model is introduced, which contains an electrostatic ideality correction to the classic Langmuir isotherm. For future materials development, these physical insights indicate that shielding effects as well as the number of independent physical sites must be considered when synthesizing effective Prussian blue analogs (PBA). In conclusion, the study provides insights into the limiting mechanisms in the physisorption of cesium cations on PB.
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| 16. |
- Nordstrand, Johan, et al.
(författare)
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Faster bipolar capacitive deionization with flow-through electrodes
- 2023
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 467
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Tidskriftsartikel (refereegranskat)abstract
- Capacitive deionization (CDI) is an emerging technology in water cleaning applications. Bipolar electrode modules are promising for upscaling CDI systems by applying a high voltage over a stack of cells. Previous experiments indicate around 3 times faster removal rate can be achieved with a 5-cell stack of flow-between electrodes. In this work, we present the first flow-through bipolar CDI design. Surprisingly, the effective average salt adsorption rate (ASAR) of a 5-cell stack was around 10 times higher per electrode mass. The flow-through design allows for faster ion transport to match the higher charging rate. Also, the floating electrodes discharge near-instantaneous by internal short-circuit upon the removal of potential, leaving almost twice as much time for charging in a cycle. Resistance is lowered due to the removal of internal compartments in the design, and the benefits of flow-through devices outweigh any potential higher energy cost of mass transport. The high voltage at the extreme electrodes poses a risk of electrode oxidation but optimized device operation controls this risk by constraining the voltage locally. For the same reason, the device is best adapted for the deionization of moderate to low ionic concentrations, such as river water, well water, or municipal water. In summary, this work provides a simpler yet highly effective way of scaling up CDI for water-cleaning applications.
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| 17. |
- Nordstrand, Johan, et al.
(författare)
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Flexible Modeling and Control of Capacitive-deionization Processes through a Linear-state-space Dynamic-Langmuir Model
- 2021
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Ingår i: npj Clean Water. - : Springer Nature. - 2059-7037. ; 4:5, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- While black-box models such as neural networks have been powerful in many applications, direct physical modeling (white box) remains crucial in many fields where experimental data are difficult or time-consuming to obtain. Here, we demonstrate with an example from desalination by capacitive deionization (CDI), how an existing physical model could be strengthened by combining a general modeling framework with physical insights (gray box). Thus, a dynamic Langmuir (DL) model is extended to a linear-state- space DL model (LDL). Results obtained show the new LDL model could incorporate general structural and operational modes, including membrane CDI and constant-current operation. The formulation removes the need for direct measurements of detailed device properties without adding model complexity, and MATLAB code for automatically implementing the model is provided in the Supplementary Information. We conclude the new LDL model is widely applicable, offering great flexibility in calibration data, and enabling prediction over general operating modes.npj
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| 18. |
- Nordstrand, Johan, et al.
(författare)
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Fully 3D modeling of electrochemical deionization
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Electrochemical deionization devices are crucial for meeting the global fresh water demands. One such is capacitive deionization (CDI), which is an emerging technology especially for brackish water desalination wherein supercapacitor devices extract salt ions from water. Here, we extend an electrolytic-capacitor (ELC)model that exploits the similarities between CDI systems and supercapacitor/battery systems. Thanks to the stability and flexibility the approach brings, the current work can present the first fully coupled and spatiotemporal 3D CDI model. This can be beneficial for investigating asymmetric CDI device structures, and the work focuses on a new generation flow-through device structure with inlet and outlet pipes at the center and corners, respectively. The results show that dead (low-flow) areas can reduce desalination rates while also raising the total leakage. However, the ionic flux in this device is still enough under normal operating conditions to ensure reasonable performance. In conclusion, researchers will now have some flexibility in designing device structures that are not perfectly symmetric (real-life case), and hence we share the model files to facilitate future research with 3D modeling of these electrochemical deionization devices.
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| 19. |
- Nordstrand, Johan, et al.
(författare)
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Fully 3D Modeling of Electrochemical Deionization
- 2023
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 8:2, s. 2607-2617
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical deionization devices are crucial for meeting global freshwater demands. One such is capacitive deionization (CDI), which is an emerging technology especially suited for brackish water desalination. In this work, we extend an electrolytic capacitor (ELC) model that exploits the similarities between CDI systems and supercapacitor/battery systems. Compared to the previous work, we introduce new implementational strategies for enhanced stability, a more detailed method of describing charge efficiency, layered integration of leakage reactions, and theory extensions to new material and operational conditions. Thanks to the stability and flexibility the approach brings, the current work can present the first fully coupled and spatiotemporal three-dimensional (3D) CDI model. We hope that this can pave the way toward generalized and full-scale modeling of CDI units under varying conditions. A 3D model can be beneficial for investigating asymmetric CDI device structures, and the work investigates a flow-through device structure with inlet and outlet pipes at the center and corners, respectively. The results show that dead (low-flow) areas can reduce desalination rates while also raising the total leakage. However, the ionic flux in this device is still enough under normal operating conditions to ensure reasonable performance. In conclusion, researchers will now have some flexibility in designing device structures that are not perfectly symmetric (real-life case), and hence we share the model files to facilitate future research with 3D modeling of these electrochemical deionization devices.
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| 20. |
- Nordstrand, Johan, et al.
(författare)
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Ladder Mechanisms of Ion Transport in Prussian Blue Analogues
- 2022
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 14:1, s. 1102-1113
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Tidskriftsartikel (refereegranskat)abstract
- Prussian blue (PB) and its analogues (PBAs) are drawing attention as promising materials for sodium-ion batteries and other applications, such as desalination of water. Because of the possibilities to explore many analogous materials with engineered, defect-rich environments, computational optimization of ion-transport mechanisms that are key to the device performance could facilitate real-world applications. In this work, we have applied a multiscale approach involving quantum chemistry, self-consistent mean-field theory, and finite-element modeling to investigate ion transport in PBAs. We identify a cyanide-mediated ladder mechanism as the primary process of ion transport. Defects are found to be impermissible to diffusion, and a random distribution model accurately predicts the impact of defect concentrations. Notably, the inclusion of intermediary local minima in the models is key for predicting a realistic diffusion constant. Furthermore, the intermediary landscape is found to be an essential difference between both the intercalating species and the type of cation doping in PBAs. We also show that the ladder mechanism, when employed in multiscale computations, properly predicts the macroscopic charging performance based on atomistic results. In conclusion, the findings in this work may suggest the guiding principles for the design of new and effective PBAs for different applications.
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| 21. |
- Nordstrand, Johan, et al.
(författare)
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Langmuir-Based Modeling Produces Steady Two-Dimensional Simulations of Capacitive Deionization via Relaxed Adsorption-Flow Coupling
- 2022
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 38:11, s. 3350-3359
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Tidskriftsartikel (refereegranskat)abstract
- The growing world population creates an ever-increasing demand for fresh drinkable water, and many researchers have discovered the emerging capacitive deionization (CDI) technique to be highly promising for desalination. Traditional modeling of CDI has focused on charge storage in electrical double layers, but recent studies have presented a dynamic Langmuir (DL) approach as a simple and stable alternative. We here demonstrate, for the first time, that a Langmuir-based approach can simulate CDI in multiple dimensions. This provides a new perspective of different physical pictures that could be used to describe the detailed CDI processes. As CDI emerges, effective modeling of large-scale and pilot CDI modules is becoming increasingly important, but such a modeling could also be especially complex. Leveraging the stability of the DL model, we propose an alternative fundamental approach based on relaxed adsorption-flow computations that can dissolve these complexity barriers. Literature data extensively validate the findings, which show how the Langmuir-based approach can simulate and predict how key changes in operational and structural conditions affect the CDI performance. Crucially, the method is tractable for simple simulations of large-scale and structurally complex systems. Put together, this work presents new avenues for approaching the challenges in modeling CDI.
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| 22. |
- Nordstrand, Johan, et al.
(författare)
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Long-term durability of commercial capacitive deionization modules
- 2024
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Ingår i: Desalination. - : Elsevier BV. - 0011-9164 .- 1873-4464. ; 576
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Tidskriftsartikel (refereegranskat)abstract
- Long-term durability is becoming increasingly relevant for capacitive deionization (CDI) as the technology emerges on the commercial scale. Short-term deionization studies have suggested that Faradaic leakages could be a major factor in electrode degradation, but the long-term effects are still unclear. In this study, we probe the degradation process of the desalination efficiency in commercial CDI modules for up to 52 days of non-stop operation. This corresponds to a little more than 100 m3 of water treated, and the lifetime production volume of the modules is estimated between 150,000–250,000 L of purified water. Surprisingly, the results demonstrate that the absolute long-term loss is largely linear with the cumulative charge leakage. This suggests short-term leakage currents could reasonably predict long-term degradation. Interestingly, the absolute loss mechanisms mean devices with higher total capacitance are more degradation resistant. Finally, shortening cycle times and other methods of reducing leakage would lead to a proportionally longer lifetime. Notably, the first 2 min of the 10 min operation retained 50 % of the performance with only 10 % of the leakage (10-fold reduction). In conclusion, the work provides a method for understanding, predicting, and reducing degradation in long-term operations with commercial CDI modules.
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| 23. |
- Nordstrand, Johan, et al.
(författare)
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Ohmic charging in capacitive deionization : efficient water desalination using capacitive spacers
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Capacitive deionization (CDI) is a promising desalination technology based on electrosorption on the surfaces ofnanoporous electrodes. However, low total dissolved solids (TDS) in the water restricts its efficacy. In this work, we develop the theory of capacitive spacers in CDI. The investigations reveal a mechanism that we call ohmic charging; that is, the resistive losses in the spacer region drive adsorption in the capacitive spacer. As a consequence, the obtained results show that such spacers can improve desalination energy efficiency, especially at ion-starved conditions. The spacers also enhance the charging rate of the electrodes because the overall resistance is lower when the current can pass the spacer material instead of the solution, through the adsorption of anions on one side and cations on the other. Going deeper, the investigations reveal a major challenge; the spacer naturally discharges on the same timescale as the electrode charging timescale. However, only the fast timescale matters with low ionic content solutions, and under these conditions the capacitive spacers are found to be superior. Put together, capacitive spacers can make a significant difference, especially when the ion concentration is low or the cycle times are short.
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| 24. |
- Nordstrand, Johan, et al.
(författare)
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Potential-driven mechanisms for raising the intercalation selectivity 100-fold in multi-ion removal from water
- 2023
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Ingår i: Desalination. - : Elsevier BV. - 0011-9164 .- 1873-4464. ; 565
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Tidskriftsartikel (refereegranskat)abstract
- Intercalation host compounds (IHC) are promising for selective ion removal from water. Recent theoretical developments have suggested that electrochemical desalination with IHC (nickel hexacyanoferrate (NiHCF)) electrodes could separate K+ and Na+ by a factor of 160. However, the experiments only produce a selectivity of around 3. In this work, we derive theory and a finite-element (FEM) model to investigate the origins of time-dependent selectivity suppression. The first results show that ion starvation can severely limit selectivity. Surprisingly, we also find that operations at low state-of-charge produce theoretical selectivity of 600, which is way above what was previously thought to be the theoretical maximum. Also surprising is that the main cause of low selectivity is that the constant-current overpotential disproportionally favors the adsorption of the ion that is less selected in the equilibrium state. By implementing short charging cycles near the depleted state with rest periods at the ends, we raised the time-dependent selectivity from 3 to 450. Even higher output selectivity could be achieved by combining IHC cathodes with membrane-less carbon anodes. In conclusion, the insights and methods derived here could enable highly selective ion removal at the device level for a wide class of IHC materials.
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| 25. |
- Nordstrand, Johan, et al.
(författare)
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Predicting and Enhancing the Ion Selectivity in Multi-Ion Capacitive Deionization
- 2020
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 36:29, s. 8476-8484
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Tidskriftsartikel (refereegranskat)abstract
- Lack of potable water in communities across the globe is a serious humanitarian problem promoting the desalination of saline water (seawater and brackish water) to meet the growing demands of human civilization. Multiple ionic species can be present in natural water sources in addition to sodium chloride, and capacitive deionization (CDI) is an upcoming technology with the potential to address these challenges because of its efficacy in removing charged species from water by electro-adsorption. In this work, we have investigated the effect of device operation on the preferential removal of different ionic species. A dynamic Langmuir (DL) model has been a starting point for deriving the theory, and the model predictions have been validated using data from reports in the literature. Crucially, we derive a simple relationship between the adsorption of different ionic species for short and long adsorption periods. This is leveraged to directly predict and enhance the selective ion removal in CDI. Furthermore, we demonstrate an example of how this selectivity could reduce excess removal of ions to avoid remineralization needs. In conclusion, the method could be valuable for predicting the impact of improved device operation on capacitive deionization with multi-ion compositions prevalent in natural water sources.
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| 26. |
- Nordstrand, Johan, et al.
(författare)
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Predicting capacitive deionization processes using an electrolytic-capacitor (ELC) model : 2D dynamics, leakages, and multi-ion solutions
- 2022
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Ingår i: Desalination. - : Elsevier BV. - 0011-9164 .- 1873-4464. ; 525
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Tidskriftsartikel (refereegranskat)abstract
- Clean water and affordable energy are critical worldwide challenges for which electrolytic capacitors are increasingly considered as viable alternatives. The upcoming technology of capacitive deionization (CDI) uses similar electrolytic capacitors for the desalination of water. The current work presents a new method that leverages existing support for supercapacitors in the form of current-distribution models, which enables detailed and separated descriptions of the rate-limiting resistances. Crucially, the new model blends this basis with a novel formulation centered on the adsorption of chemical species in CDI. Put together, it is adaptable to solving a wide range of problems related to chemical species in electrochemical cells. The resulting electrolytic-capacitor (ELC) model has enhanced stability and ease-of-implementation for simulations in 2D. The results demonstrate that the model accurately simulates dynamics CDI performance under a variety of operational conditions. The enhanced stability together with the adaptability further allows tractable simulations of leakage reactions and even handling multi-ion deionization in 2D. Moreover, the model naturally blends with existing interfaces in COMSOL Multiphysics, which automatically generalizes, stabilizes, and simplifies the implementation. In conclusion, the ELC model is user-friendly and tractable for standard simulations while also being especially powerful when simulating complex structures, leakage reactions, and multi-ion solutions.
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| 27. |
- Nordstrand, Johan, et al.
(författare)
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Relaxed Adsorption-flow Coupling Enables Stable COMSOL Modeling of Upscaled Capacitive Deionization
- 2020
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Konferensbidrag (refereegranskat)abstract
- The rapidly increasing world population will dramatically expand the future global freshwater requirements, now making lots of researchers realize the fundamental importance of developing effective desalination technologies. Hence, the emerging capacitive deionization (CDI) desalination technique is increasingly grabbing the attention of researchers. Simulation of capacitive desalination brings critical value for the understanding, prediction, and optimization of the CDI process which works on the principles of charging and discharging supercapacitors. Typically, a CDI cell comprises two porous electrodes separated by a nonconducting spacer, wherein it produces freshwater by allowing an applied voltage to rapidly extract the salt ions from the steadily passing water steam (during charging of the supercapacitor). Similarly, the electrodes are regenerated by discharging the adsorbed ions into a waste stream. Previous modeling attempts use the seminal state-of-the-art 2D-FEM method which simulates ion transport coupled with an electric-double-layer (EDL) adsorption formulation. There, the COMSOL PDE interface implements large systems of interconnected adsorption-flow PDEs, and the resulting model was usually found to be “unsteady”. In contrast, in the present work, we reinterpret the phenomena from a porous-catalyst perspective, which fundamentally breaks through the complexity wall by naturally relaxing the adsorption-flow coupling. Specifically, the Brinkman Equations simulated generalized water-flow patterns, which became the background flow in a Multiphysics-coupled Transport of Diluted Species in Porous Media. The latter thus effectively simulates both ionic transport and, through the Reactions interface, the time-dependent ion adsorption. Here, an accurate 0D Randles-circuit model pre-calculates the reaction rate to reduce simulation complexity. This approach reduces the detailed resolution but retains the ability to identify localized phenomena such as concentration shocks, and reaches the state-of-the-art performance in simulating global experimental metrics, as validated with literature data. Additionally, the decoupled Brinkman-flow calculations enable broad flow simulations and simulating the flow efficiency in complex and upscaled CDI structures. Ultimately, the approach means the new model greatly improves stability and broadly opens up research to large interconnected modules and nonlinear flow patterns. As the CDI field continues to grow, these large-scale systems will become increasingly important modeling targets, and we fundamentally believe this work will facilitate and promote future COMSOL studies in modular CDI design.
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| 28. |
- Nordstrand, Johan, et al.
(författare)
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Simplified Prediction of Ion Removal in Capacitive Deionization of Multi-Ion Solutions
- 2020
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Ingår i: Langmuir. - : AMER CHEMICAL SOC. - 0743-7463 .- 1520-5827. ; 36:5, s. 1338-1344
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Tidskriftsartikel (refereegranskat)abstract
- Capacitive deionization (CDI) is an upcoming desalination technology being increasingly considered to be a simple and cost-effective solution for brackish water, where electrosorption leads to the removal of charged species from water. Real-world water samples typically contain a multitude of ions that must be considered apart from sodium-chloride salt. In this work, we have developed a method to quantify the competitive adsorption of different ionic species during CDI processes. The method is straightforward, requiring a single calibrating experiment to extract a 'periodic table' of competitiveness scores for all ions present in the experiment. Using a dynamic Langmuir model that was developed by our group, it is shown that these scores could subsequently be used to predict the adsorption of any ion species in a multi-ion solution. Excellent agreement with data from the literature could be achieved with this model, and the method is especially well-suited for trace ions as these can be predicted directly. The derived method is simple and accurate for quantifying and predicting adsorption in multi-ion solutions and could be valuable for predicting the effect when applying CDI to real-world water samples.
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| 29. |
- Nordstrand, Johan, et al.
(författare)
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Sodium to cesium ions: a general ladder mechanism of ion diffusion in prussian blue analogs
- 2022
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:20, s. 12374-12382
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Tidskriftsartikel (refereegranskat)abstract
- Prussian blue analogs (PBAs) form crystals with large lattice voids that are suitable for the capture, transport and storage of various interstitial ions. Recently, we introduced the concept of a ladder mechanism to describe how sodium ions inside a PBA crystal structure diffuse by climbing the frames formed by aligned cyanide groups in the host structure. The current work uses semi-empirical tight-binding density functional theory (DFTB) in a multiscale approach to investigate how differences in the size of the monovalent cation affect the qualitative and quantitative aspects of the diffusion process. The results show that the ladder mechanism represents a unified framework, from which both similarities and differences between cation types can be understood. Fundamental Coulombic interactions make all positive cations avoid the open vacant areas in the structure, while cavities surrounded by partially negatively charged cyanide groups form diffusion bottlenecks and traps for larger cations. These results provide a new and quantitative way of understanding the suppression of cesium adsorption that has previously been reported for PBAs characterized by a low vacancy density. In conclusion, this work provides a unified picture of the cation adsorption in PBAs based on the newly formulated ladder mechanism.
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| 30. |
- Nordstrand, Johan
(författare)
-
SofTer : Theory, software, and video tutorial for simulating capacitive deionization with tertiary current distributions
- 2023
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Ingår i: Desalination. - : Elsevier BV. - 0011-9164 .- 1873-4464. ; 566
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Tidskriftsartikel (refereegranskat)abstract
- Capacitive deionization (CDI) is a desalination method that has been expanding substantially in recent years. As processes are getting more complex, corresponding developments in theory and software are necessary to keep up and drive future research. In this work, we derive a new CDI theory based on a tertiary current distribution, meaning each ionic species is resolved individually in a unified framework in 1D/2D. The results show that this approach is ideal for simulations with multiple ionic species and materials that affect cations and anions differently. Direct examples include such as intercalation materials and membranes. It is also effective for incorporating electrode replenishment in flow-electrode CDI (FCDI). By benchmarking with traditional methods, we demonstrate that numerical stability is a central limitation of traditional methods for these applications. The results identify physical processes involving rapid changes to cause major instabilities. This can thus be handled by introducing specific numerically stabilizing factors. Finally, the theory is compiled into comprehensive software that researchers can straightforwardly apply in future studies without having to reconstruct methods from scratch. A corresponding video tutorial has also been deposited. In conclusion, the work pushes the limits of the simulation capabilities in a wide range of CDI processes.
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| 31. |
- Nordstrand, Johan, et al.
(författare)
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Theory of bipolar connections in capacitive deionization and principles of structural design
- 2022
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 430, s. 141066-
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Tidskriftsartikel (refereegranskat)abstract
- Capacitive deionization (CDI) is an emerging desalination technique for which upscaling is increasingly relevant for practical applications. Recent research has suggested using bipolar stacks for fast charging and effective energy recovery, but contradicting results have been reported. In this work, we use circuit modeling and finite element (FEM) simulations to understand both the ideal and non-ideal behavior of these systems. This bottom-up approach shows that charging with the ideal bipolar connection is faster proportionally to the total number of cells in a stack. The identified reason for this gain is that the electrical resistance is mainly external, and the same current charges all cells in the stack. Better still, the maximum charge and energy consumption are the same as in the unipolar case. However, the bipolar setup will experience short-circuit if there is insufficient isolation of the solution between the cell compartments. Conversely, the improved adsorption will be nullified if there is sub-stantial resistance in the floating current collectors separating the compartments. In conclusion, bipolar con-nections have lots of potential, and developments in the internal separators between cells could be massively beneficial for future upscaled CDI devices.
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| 32. |
- Nordstrand, Johan, et al.
(författare)
-
Three-Dimensional Model for Capacitive Deionization
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Electrochemical deionization devices are crucial for meeting global freshwater demands. One such is capacitive deionization (CDI), which is an emerging technology especially suited for brackish water desalination. In this work, we extend an electrolytic-capacitor (ELC) model that exploits the similarities between CDI systems and supercapacitor/battery systems. Thanks to the stability and flexibility the approach brings, the current work can present the first fully coupled and spatiotemporal 3D CDI model. This can be beneficial for investigatingasymmetric CDI device structures, and the work investigates a flow-through device structure with inlet and outlet pipes at the center and corners, respectively. The results show that dead (low-flow) areas can reduce desalination rates while also raising the total leakage. However, the ionic flux in this device is still enough under normal operating conditions to ensure reasonable performance. In conclusion, researchers will now have some flexibilityin designing device structures that are not perfectly symmetric (real-life case), and hence we share the model files to facilitate future research with 3D modeling of these electrochemical deionization devices.
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| 33. |
- Nordstrand, Johan, et al.
(författare)
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Tuning the Cation/Anion Adsorption Balance with a Multi-Electrode Capacitive-Deionization Process
- 2023
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 170:2, s. 023502-
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Tidskriftsartikel (refereegranskat)abstract
- Capacitive deionization (CDI) is an emerging technique for purifying water by removing ions. Recent experimental studies have reported that the anion/cation adsorption can be naturally imbalanced, even for a solution with just sodium and chloride, and suggested a link between imbalance and Faradaic leakages. However, these effects have been missing from conventional models. In this work, we developed a new circuit model to better understand the connection between Faradaic leakages and adsorption imbalance. The theory demonstrates that the effect emerges in a model that includes leakages, considers leakages on both electrodes separately, and considers different leakage resistance on the two electrodes. Having the model, it is possible to analyze and quantify the influence of the leakage resistance and other material properties on the adsorption imbalance. Leveraging these results, we further present a multi-electrode (ME) device design. The setup adds a third electrode to the spacer channel and can tune or eliminate the adsorption imbalance based on appropriately distributing the voltage across the electrodes. In conclusion, we describe a charge leakage mechanism responsible for the imbalance of ion adsorption and a flexible device design to tune the anion/cation removal.
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| 34. |
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| 35. |
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| 36. |
- Pulkkinen, Kirsi, et al.
(författare)
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Does It Really Matter? Assessing the Performance Effects of Changes in Leadership and Management Structures in Nordic Higher Education
- 2019. - 1
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Ingår i: Reforms, Organizational Change and Performance in Higher Education<em></em>. - Cham : Palgrave Macmillan. ; , s. 3-36
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Bokkapitel (refereegranskat)abstract
- Universities are public organisations, which operate in a highly institutionalised environment. They are heavily dependent on public resources. As such, universities are susceptible to shifts in governance arrangements but are also far from being passive recipients of reform agendas. They face demands from multiple internal constituencies (academics, administrators, students, managers) and from a variety of external stakeholders. This chapter explores the interplay between governance arrangements resulting from policy shifts and university dynamics. It sets the stage for the book, asking the following research questions: (1) what characterises changes in governance regimes in Nordic universities in the last decade and a half, and (2) what effects have these changes had in the evolution of higher education systems? The chapter takes a comparative approach and identifies similarities and differences across the Nordic countries. This chapter serves as a frame of reference for the book and includes a common methods and data section.
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| 37. |
- Söderlind, Johan, et al.
(författare)
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National Performance-Based Research Funding Systems : Constructing Local Perceptions of Research?
- 2019
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Ingår i: Reforms, Organizational Change and Performance in Higher Education. - Cham : Palgrave Macmillan. - 9783030117375 ; , s. 111-144
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Bokkapitel (refereegranskat)abstract
- In recent years, performance-based research funding systems (PRFSs) have been introduced in all of the Nordic countries. In this chapter, we compare these systems and explore how their introduction is reflected within universities. Through interviews with academics, managers and administrators, we study how the performance measures of these systems are used at the university level and how that affects research activities. The results indicate that the introduction of PRFSs at the national level have had significant effects at the institutional level. The PRFSs contribute to the institutionalisation and consolidation of research metrics as the main way to describe research performances, and thus as the organising principles of research. Differences are also noted between the countries in the reactions of the university actors, which are believed to be a consequence of the variations of the PRFSs.
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| 38. |
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