Abstract Prussian Blue Analogues (PBAs), which are characterized by their open structure, high stability, and non-toxic properties, have recently been the subject of research for various applications, including their use as electrode precursors for capacitive deionization, gas storage, and environmental purification. These materials can be readily tailored to enhance their affinity towards gases for integration with sensing devices. An improved understanding of PBA-gas interactions is expected to enhance material development and existing sensor deposition schemes greatly. The use of inverse gas chromatography (IGC) is a robust approach for examining the relationship between porous materials and gases. In this study, the adsorption properties of (functionalized) hydrocarbons, i.e., probe molecules, on the copper hexacyanoferrate (CuHCF) lattice were studied via IGC, demonstrating that alkylbenzenes have a higher affinity for this material than n-alkanes. This difference was rationalized by steric hindrance, π–π interactions, and vapour pressure effects. Along the same line, the five isomers of hexane showed decreasing selectivity upon increased steric hindrance. Enthalpy values for n-pentane, n-hexane and n-heptane were lower than that of toluene. The introduction of increased probe masses resulted in a surface coverage of 46% for toluene. For all n-alkane probe molecules this percentage was lower. However, the isotherms of these probes did not show saturation points and the observed linear regime proves beneficial for gas sensing. Our work demonstrates the versatility of CuHCF for gas sensing purposes and the potential of IGC to characterize the adsorption characteristics of such a porous nanomaterial.

The decoupled power and energy output of a redox flow battery (RFB) offers a key advantage in long-duration energy storage, crucial for a successful energy transition. Iodide/iodine and hydrogen/water, owing to their fast reaction kinetics, benign nature, and high solubility, provide promising battery chemistry. However, H2-I2 RFBs suffer from low open circuit potentials, iodine crossover, and their multiphase nature. We demonstrate a H2-I2 operation with a combined neutral-pH catholyte (I3 -/I-) and an alkaline anolyte (KOH), producing an open circuit cell voltage of 1.28 V. Additionally, we incorporate a pressure-balanced gas diffusion electrode (GDE) to mitigate mass transport limitations at the anode. These improvements result in a maximum power density of 230 W/m2 when allowing a mild breakthrough of H2 through the GDE. While minimal crossover occurs, side reactions of permeating active species were found reversible, enabling long-term operation. Future work should address the stability of the GDE and optimization of the electrolyte thickness and concentration to fully leverage the potential unlocked by balancing the pressure and pH in the H2-I2 RFB.

Reverse electrodialysis (RED) is a technology to generate electricity from two streams with different salinities. While RED systems have been conventionally used for electricity generation, recent works explored combining RED for production of valuable gases. This work investigates the feasibility of producing hydrogen and chlorine in addition to electricity in an RED stack and identifies potential levers for improvement. A simplified one-dimensional model is adopted to assess the technical and economic feasibility of the process. We notice a strong disparity in typical current densities of RED fed with seawater and river water and that in typical water (or chlor-alkali) electrolysis. This can be partly mitigated by using brine and seawater as RED feeds. Considering such an RED system, we estimate a hydrogen production of 1.37 mol/(m2 h) and an electrical power density of 1.19 W/m2. Although this exceeds previously reported hydrogen production rates in combination with RED, the levelized costs of products are 1-2 orders of magnitude higher than the current market prices at the current state. The levelized costs of products are very sensitive to the membrane price and performance. Hence, going forward, manufacturing thinner and highly selective membranes is required to make the system competitive against the consolidated technologies.

Selective ion separation via capacitive deionization (CDI) is of relevance because of its environmental and in-dustrial applications in water purification and softening, heavy metal removal, and resource recovery. Conventionally, carbon electrodes and ion-selective membranes have been used for selective removal of anions and cations. In this study, we engineered a CDI cell with two identical NiHCF electrodes, separated by an anion-exchange membrane coated with a polyelectrolyte multilayer (PEM), for simultaneous and selective separation of monovalent over divalent anions and cations. The modified membrane rejects divalent over monovalent anions while the NiHCF electrodes selectively adsorb monovalent over divalent ions. A separation factor (beta) of 7 < beta < 14 was obtained for Cl- over SO42-, while an average beta of & AP; 17 was obtained for Na+ over Mg2+, reflecting the preference of the modified membrane and the electrodes, respectively. Moreover, this preference was preserved at low concentrations of monovalent ions as well. This tandem use of intercalation electrodes and a PEM membrane provides a new and facile method for simultaneous cation and anion selectivity in CDI, opening new avenues for enhanced and tunable separations from complex ion mixtures

Selective removal of ions from water via capacitive deionization (CDI) is relevant for environmental and industrial applications like water purification, softening, and resource recovery. Prussian blue analogs (PBAs) are proposed as an electrode material for selectively removing cations from water, based on their size. So far, PBAs used in CDI are selective toward monovalent ions. Here, vanadium hexacyanoferrate (VHCF), a PBA, is introduced as a new electrode material in a hybrid CDI setup to selectively remove divalent cations from water. These electrodes prefer divalent Ca2+ over monovalent Na+, with a separation factor, βCa/Na ≈3.5. This finding contrasts with the observed monovalent ion selectivity by PBA electrodes. This opposite behavior is understood by density functional theory simulations. Furthermore, coating the VHCF electrodes with a conducting polymer (poly‐pyrrole, doped with poly‐styrenesulphonate) prevents the contamination of the treated water following the degradation of the electrode. This facile and modular coating method can be effortlessly extended to other PBA electrodes, limiting the extent of treated water contamination during repeated cycling. This study paves the way for tunable selectivity while extending the library of electrodes that can be successfully used in (selective) CDI.

Fishing ions: this review provides a comprehensive analysis of different approaches in utilizing capacitive deionization (CDI) for selective ion separations and ion removal.

Selective ion removal has been a point of focus in capacitive deionization because of its industrial applications such as water purification, water softening, heavy metal separation and resource recovery. Conventionally, carbon is used as electrode material for selectivity. However, recent developments focus on intercalation materials such as Prussian Blue Analogues, due to their size-based preference towards cations. Selectivity of nickel hexacyanoferrate electrodes from a mixture of Na+, Mg2+, and Ca2+ ions was studied in this work. Here, a CDI cell with two identical NiHCF electrodes was operated in two desalination modes: (a) cyclic, in which ions are removed from and released into the same water reservoir and thus, the ion concentration remains the same after one cycle, and (b) continuous, in which ions are removed from one water reservoir and released back in a different reservoir. An average separation factor of ≈15 and 25, reflecting the selectivity of the electrodes, was obtained for Na+ over Ca2+ and Mg2+ from an equimolar solution of Na+, Ca2+ and Mg2+ in both, cyclic and continuous desalination. It was concluded that NiHCF, used in a symmetric CDI cell, is a promising material for highly selective removal of Na+ from a multivalent ion mixture.

Capacitive deionization (CDI) is a water desalination technology in which ions are removed from water by creating a potential difference between two capacitive electrodes. Porous carbon has been extensively used as an electrode material in CDI. However, recent developments in the field of intercalation materials have led to their application in CDI due to their large ion storage capacity. One such intercalation material, nickel hexacyanoferrate (NiHCF), was used in this study as the electrode material. A symmetrical cell was assembled with two identical NiHCF electrodes separated by an anion-exchange membrane. The effect of operational parameters such as current density, feed concentration and flow rate on the desalination characteristics of the cell was investigated. The highest salt adsorption capacity of approximate to 35 mg/g was measured at a current density of 2.5 A/m(2) in a 20 mM NaCl feed solution. Furthermore, a Nernst-Planck transport model was successfully used to predict the change in the outlet concentration and cell voltage of the symmetric CDI cell. Finally, performance of the symmetric NiHCF CDI cell was compared with an MCDI cell with porous carbon electrodes. The NiHCF cell, on average, consumed 2.5 times less energy than the carbon-based MCDI cell to achieve similar levels of salt removal from saline water in CDI.

Capacitive deionization is a water desalination technology in which ions are stored in electrodes in an electrochemical cell construction, connected to an external circuit, to remove ions present in water from various sources. Conventionally, carbon has been the choice of material for the electrodes due to its low cost, low contact resistance and high specific surface area, electronic conductivity, and ion mobility within pores. The ions in the water are stored at the pore walls of these electrodes in an electrical double layer. However, alternative electrode materials, with a different mechanism for ion and charge storage, referred to as ion intercalation, have been fabricated and studied as well. The salt adsorption performance exhibited by these materials is in most cases higher than that of carbon electrodes. This work traces the evolution of the study of redox activity in these intercalation materials and provides a chronological description of major developments in the field of Capacitive Deionization (CDI) with intercalation electrodes. In addition, some insights into the cell architecture and operation parameters are provided and we present our outlook of future developments in the field of intercalation materials for CDI.

We detail the analysis of centrifugal homogenization process by a hydrodynamic model and the model-guided design of a low-cost centrifugal homogenizer. During operation, centrifugal force pushes a multiphase solution to be homogenized through a thin nozzle, consequently homogenizing its contents. We demonstrate and assess the homogenization of coarse emulsions into relatively monodisperse emulsions, as well as the application of centrifugal homogenization in the mechanical lysis of mpkCCD mouse kidney cells. To gain insight into the homogenization mechanism, we investigate the dependence of emulsion droplet size on geometrical parameters, centrifugal acceleration, and dispersed phase viscosity. Our experimental results are in qualitative agreement with models predicting the droplet size. Furthermore, they indicate that high shear rates kept constant throughout operation produce more monodisperse droplets. We show this ideal homogenization condition can be realized through hydrodynamic model-guided design minimizing transient effects inherent to centrifugal homogenization. Moreover, we achieved power densities comparable to commercial homogenizers by model guided optimization of homogenizer design and experimental conditions. Centrifugal homogenization using the proposed homogenizer design thus offers a low-cost alternative to existing technologies as it is constructed from off-the-shelf parts (Falcon tubes, syringe, needles) and used with a centrifuge, readily available in standard laboratory environment.

We present a porous electrode theory for capacitive deionization with electrodes containing nanoparticles that consist of a redox-active intercalation material. A geometry of a desalination cell is considered which consists of two porous electrodes, two flow channels, and an anion-exchange membrane, and we use the Nernst-Planck theory to describe ion transport in the aqueous phase in all these layers. A single-salt solution is considered, with unequal diffusion coefficients for anions and cations. Similar to previous models for capacitive deionization and electrodialysis, we solve the dynamic two-dimensional equations by assuming that the flow of water, and thus the advection of ions, is zero in the electrode, and in the flow channel only occurs in the direction along the electrode and membrane. In all layers, diffusion and migration are only considered in the direction perpendicular to the flow of water. Electronic as well as ionic transport limitations within the nanoparticles are neglected, and instead the Frumkin isotherm (or regular solution model) is used to describe local chemical equilibrium of cations between the nanoparticles and the adjacent electrolyte, as a function of the electrode potential. Our model describes the dynamics of key parameters of the CDI process with intercalation electrodes, such as effluent salt concentration, the distribution of intercalated ions, cell voltage, and energy consumption.

Thermal power plants in India emit around 500Mt of CO2 annually. All of it is released into the atmosphere untreated. Microalgae, a third generation feedstock for bio-fuel emerges as a viable option for partly sequestering the emissions. Moreover, its carbon capture capacity of 4.8kg CO2/kg biomass, which is very much as compared to terrestrial substitutes like Jhatropa curcas, enables to produce bio fuel hence adding value to the entire process. This paper intends to build upon this idea and come up with strategies to integrate bio fuel production and CO2 sequestration with the existing thermal power plants. The raw materials needed for algal growth are available in the plant as elaborated in the paper. Thus the bio fuel produced can be routed back to power the plant consequently lowering the dependence on coal. This would help in putting a check on the carbon emissions thus making the existing systems more environmentally benign and suitable for long haul. This paper reviews currently employed carbon capture technologies and methods and comes up with a strategy to subsume carbon capture through microalgae with power plants of a certain capacity. 3t/day is taken as the basis for calculations in the proposed flow sheet. An alternative of the above is also provided which substitutes the biofuel production with co-firing. This escalates the nitrogen content of flue gas but deescalates the investment. This brings down the capital investment in the plant but enhances N2 content of flue gas. Carbon leakage is accounted for in a table of atomic balance. It takes care of input and output of carbon. The paper is inclined towards the conclusion that the Microalgae possess incredible potential and if tapped efficaciously could prove to be extremely helpful in these days of power and environmental crisis.

Treatment of water for domestic and industrial use is an ubiquitous process today. This treatment can be physical, chemical, or biological and is usually performed in multiple steps. The removal of salts and minerals from water is one such step that is of high priority. This removal is referred to as water desalination. This may include production of water for domestic and industrial use, harvesting/recovering materials (salts/ions) of value and removing harmful species by selectively separating them from water. In this regards, electro-driven processes have gained attention due to their easy operation, mild environmental impact, and potentially low energy consumption. Capacitive Deionization (CDI), investigated in this work, is one such promising electro-driven ion separation technology. Conventionally, it employs capacitive electrodes that store ions removed from waste water and the energy input to these electrodes can be regenerated during their regeneration. Since the ion removal relies heavily on the ability of the electrodes to store them, investigation into new - and development of existing - electrode material forms the main focus of the research carried out in the field of CDI. The development of an electrode material involves focusing the ion adsorption capacity, the rate of ion adsorption/desorption, the inherent or functionalized capability to selectively store ions and long-term stability. The research presented in this thesis and the conclusions obtained from them address these developmental challenges. In particular, this work focuses on Prussian blue analogues (PBAs). PBAs are crystalline in nature and in general, the elements constituting a PBA lattice are assembled in a cubic structure with metals transition metals connected by −C≡N− (cyanide) ligand. These lattices are capable of storing cations into the interstitial sites formed in these lattices. This is referred to as intercalation. The use of PBAs in CDI has attracted attention because of their open crystal structure, customizable chemical composition, higher equilibrium salt adsorption capacity via cation intercalation compared to carbon, and an inherent selectivity among cations. In this work, the use of non-carbon based electrodes was chronicled throughout literature. Following that, the ability of PBA as an electrode materials was assessed by using them to deionize brackish water in an electrochemical flow cell under the influence of an electric current. Furthermore, their capability to selectively remove cations from waste water was also tested. It was found that a cell containing PBA electrodes required on average two times less energy than a cell containing conventionally and commonly used carbon electrodes. From the investigation into the ion selectivity of these electrodes, it was observed that nickel containing PBA was highly selective towards monovalent ions while the vanadium containing PBA exhibited preference towards divalent ions, indicating that the ion-selective nature of PBA is customizable. Along the same lines, an electrochemical cell was also developed that contained monovalent cation-selective PBA and a monovalent anion-selective anion exchange membrane, providing ion selectivity of cations and anions simultaneously. In addition to experiments, a theoretical understanding was developed at physical level to predict the performance of an electrochemical cell containing PBA electrodes. This work systematically presents an investigation into an alternative electrode material in CDI and reflects on the future of intercalation electrodes within the framework of (selective) ion separation.