Salt Systems Research Articles

Molten Salt-Assisted Synthesis of Catalysts for Energy Conversion.

A breakthrough in manufacturing procedures often enables people to obtain the desired functional materials. For the field of energy conversion, designing and constructing catalysts with high cost-effectiveness is urgently needed for commercial requirements. Herein, the molten salt-assisted synthesis (MSAS) strategy is emphasized, which combines the advantages of traditional solid and liquid phase synthesis of catalysts. It not only provides sufficient kinetic accessibility, but effectively controls the size, morphology, and crystal plane features of the product, thus possessing promising application prospects. Specifically, the selection and role of the molten salt system, as well as the mechanism of molten salt assistance are analyzed in depth. Then, the creation of the catalyst by the MSAS and the electrochemical energy conversion related application are introduced in detail. Finally, the key problems and countermeasures faced in breakthroughs are discussed and look forward to the future. Undoubtedly, this systematical review and insights here will promote the comprehensive understanding of the MSAS and further stimulate the generation of new and high efficiency catalysts.

Li2O concentration influenced local structure and properties of molten LiCl salt by machine learning driven molecular dynamics simulation

Pyroprocessing is one of the promising technologies for the reprocessing of spent nuclear fuel. In the electrolytic reduction process of pyroprocessing, LiCl serves as the electrolyte with a minor addition of Li2O as the initial oxygen ion input. Investigating the impact of Li2O concentration on the molten salt system is essential for enhancing the efficiency of electrolytic reduction. In the present study, the LiCl-Li2O system is simulated using deep potential molecular dynamics simulation. The properties including self-diffusion coefficient, shear viscosity, ionic conductivity, heat capacity, radial distribution functions, coordination numbers, short-range order, medium-range order, Voronoi structure, and angle distribution functions are explored at different Li2O concentrations. This study reveals that the variations of physical properties at different Li2O concentrations in LiCl molten salt can be attributed to the changes in local structure. For example, unnormal high proportions of two Voronoi structures are found in the molten salt when the Li2O concentration increases, which may explain the changes of properties. These findings offer valuable insights for refining the parameters of electrolytic reduction and elucidating the correlation between microscopic and macroscopic phenomena.

Cathodic Decomposition Electrodes as Standard Reference Electrodes for Molten Salts: Example of the Lithium Eutectic Electrode for the LiCl-KCl Eutectic

Alternatives to the widely-used standard anodic decomposition reference electrodes in molten salts are necessary to enable more easily reproduced thermochemical and electrochemical data in molten salt electrolytes. The class of standard reference electrodes called cathodic decomposition electrodes (CDEs) are easily constructed and can be used to make thermochemical measurements in molten salts more directly compared to anodic decomposition electrodes. The lithium eutectic electrode (LEE) was chosen as a sample test case for validation and was applied to thermochemical measurements of electroactive species in molten LiCl-KCl eutectic. Transient measurements were made to measure the Li+/Li reduction potential at zero current in pure LiCl-KCl eutectic relative to a Li-alloy reference electrode to validate the reference potential of the LEE. Literature-reported electromotive force measurements against Li-alloy reference electrodes were used to generate a relationship between the LEE and the standard chlorine electrode and this relationship was used to evaluate measured and reported formal potential measurements for the LiCl-KCl-GdCl3 system. This work demonstrates the general framework for defining CDEs for any molten salt system and a method for calibrating external reference electrodes against a CDE standard reference electrode, improving the ease of obtaining thermochemical and electrochemical measurements in any molten salt system.

Microwave-assisted alkaline fusion followed by water-leaching for the selective extraction of the refractory metals tungsten, niobium and tantalum from low-grade ores and tailings

The refractory metals tungsten, tantalum and niobium are considered critical raw materials in Europe. Diversifying the supply of such materials, for instance by recovering refractory metals from local low-grade ore materials could reduce their supply risks. However, the extraction processes require to be efficient with a low energy and material consumption and a minimal environmental impact. In this work, microwave (MW) assisted alkaline fusion was explored to extract tungsten from scheelite containing ore materials with different grades (high to very low) and tantalum and niobium from a columbite-tantalite [(Fe,Mn)(Nb,Ta)2O6] concentrate. During the fusion process scheelite was converted into soluble alkali tungstate salts [Na2WO4, K2WO4 and/or K3Na(WO4)2] and the reaction temperature could be lowered to 150–200 °C by fusion with a low-melting eutectic alkali salt system of an 1:1 (m/m) NaOH:KOH mixture. The application of MW-assisted heating allowed for fast and volumetric heating, thereby lowering reaction times to 10 min – 30 min. After fusion, tungsten was extracted by a simple water leaching step leading to extraction efficiencies ranging from 77 % to 97 %. Noteworthily, also P, S and As, which all form soluble oxyanions were extracted from the studied materials. Extraction of niobium and tantalum was also achieved though MW-assisted alkaline fusion as an alternative to acidic fluorine-based hydrometallurgical processes. MW-assisted heating allowed for a fast conversion of the (Fe,Mn)(Nb,Ta)2O6 into alkali tantalate and niobate salts. Under optimal conditions, MW-assisted fusion with KOH (salt:sample = 3:1 (m/m)) at 400 °C for 10 min leached ca. 74 %–88 % of tantalum and 77 %–86 % of niobium into water (L/S=10) at 40 °C for 120 min, while the main matrix elements Mn and Fe displayed limited dissolution (<4%). Due to the low solubility of sodium tantalate and niobate salts in water, MW-assisted alkaline fusion in an eutectic NaOH:KOH mixture followed by water leaching was not efficient.

Application Properties of Gemini Quaternary Ammonium Salt with Quadra‐cationic Sites and Sodium Fatty Alcohol Polyoxyethylene Ether Carboxylate Mixed Systems

AbstractThe application properties such as foam property, electrolyte tolerance, antibacterial activity and antistatic performance of the mixed systems of a novel Gemini quaternary ammonium salt with quadra‐cationic sites (TC‐GS) and sodium fatty alcohol polyoxyethylene ether carboxylate (AE9CNa) at various molar fraction of TC‐GS (αTC‐GS), were investigated systematically. Results show that TC‐GS/AE9CNa mixed systems with different ratios form a homogeneous and transparent solution, which exhibits excellent foam stability and antibacterial activity. The foam volume of the mixed system remains nearly constant from 400 s to 1000 s, and even when TC‐GS is 10 mg/L in the mixed systems, the antibacterial rates against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) for 2 min. are all exceeded 99 %. The mixed systems of TC‐GS/AE9CNa at various αTC‐GS also demonstrate the superior electrolyte tolerance, their maximum tolerance of NaCl, CaCl2 and MgCl2 is severally beyond 270 g/L, 180 g/L and 180 g/L. In addition, both TC‐GS solution and the mixed systems have good antistatic properties, which can reduce the surface resistance of polyester fabric to ≤1010 Ω.

A Planar-Cavity Receiver Configuration for High-Temperature Solar Thermal Processes

Next-generation concentrating solar thermal power (CSP) technologies target a wide spectrum of applications including electricity generation, thermochemical processes, and industrial process heat for broad decarbonization potential. Many of these applications require higher temperatures than those of current commercial nitrate salt systems. Particulate materials are promising candidates for next-generation high-temperature heat transfer and low-cost storage media and can facilitate operation over a wide temperature range. However these materials necessitate novel receiver configurations to accept the high incident flux concentrations that enable high solar-to-thermal receiver efficiency. One option is a novel light-trapping planar cavity receiver configuration in which small cavity-like structures are formed from opaque planar surfaces such that a high incident flux concentration at the cavity aperture is reduced to a wall-absorbed solar flux concentration that is manageable within limited wall-to-particle heat transfer rates. The paper introduces the receiver configuration and provides calculated optical performance for a preliminary 50 MWt receiver design.

Diffusion Behaviors of CaCl2-NaCl Molten Salt under an Electric Field: A Deep Potential Molecular Dynamics Simulation.

CaCl2-NaCl molten salt is one of the widely used electrolytes, and the effect of the electric field on it needs to be considered in the environment of manufacturing metals and alloys as well as in battery applications. To be closer to the state of the CaCl2-NaCl molten salt system in practical applications, this study uses the training-based deep potential, combined with the ionic structure, to analyze the electric field effects on the drift velocity, ionic mobility, ion diffusion, and viscosity of the CaCl2-NaCl system by molecular dynamics simulations. It is shown that the electric field has a stronger effect on the ion diffusion behavior parallel to the direction of the electric field in the CaCl2-NaCl molten salt system. Due to the looser coordinate structure of Na+, the interaction force between Na-Cl is small compared with that between Ca-Cl. Na+ is easily driven and more sensitive to the electric field, whose drift velocity, ionic mobility, and diffusion coefficient are larger than those of the other two ions, with an order of Na+ > Cl- > Ca2+. All ionic drift velocities increase linearly as electric field intensity increases and the ionic mobilities tend to be constant. The diffusion coefficient parallel to the direction of the electric field exponentially increases and the viscosity tends to exponentially decrease with the increase in the electric field intensity. This work is important for accurately predicting the properties and performance of molten salts and their improvement for applications such as solar thermal energy conversion.

Computational insights into the structural, thermodynamic and transport properties of CaF2-MgF2 binary fluoride system at high temperatures

The structural, thermodynamic and transport properties of the CaF2-MgF2 molten salt system were investigated with ab initio molecular dynamics (AIMD), system-specific neural network interatomic potentials (NNIPs) and universal PreFerred Potentials (PFP). We trained an NNIP model using AIMD data as input and used this potential to efficiently simulate the interactions within a large supercell in a temperature range of 1273–1773 K. The Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code was employed to validate our trained NNIP model. The Matlantis software with universal PFP is also presented to prove its feasibility for MD calculations and can be considered as a useful alternative simulation tool for higher-order systems where existing potentials are not readily available. We calculated structural and thermodynamic properties including radial distribution function (RDF), angular distribution function (ADF), specific heat capacity, ionic self-diffusivity, and viscosity. Our results indicate that the system exhibited a high degree of structural disorder, with the Ca, Mg, and F ions forming a liquid solution. Using PFP, the positions of the first peak in RDFs for Ca-F and Mg-F pairs are only slightly left-shifted (<0.05 Å), and the estimated viscosity of the melt decreases from 4.613 mPa·s to 1.846 mPa·s with an increase in temperature from 1273 K to 1773 K, in agreement with the NNIP trained specifically for CaF2-MgF2. Our results provide valuable insights into the properties of the CaF2-MgF2 system at high temperatures and serve as predictive models for the development of new electrolytes that could be used for silicon epitaxy by adding silica.

Model for predicting oil testing fluid rheological parameters of Bohai Bay oilfield in wide temperature and pressure range

The rheological parameters of oil testing fluids play a crucial role in safely conducting oil testing operations, protecting reservoirs, and maintaining wellbore integrity, which are greatly influenced by temperature and pressure. This article conducted rheological experiments on commonly used potassium salt polymer systems and organic salt systems for oil testing fluids in the Bohai Bay Oilfield under 4–200 °C and 30–150 MPa. The experiments revealed the variation of rheological parameters with temperature and pressure. Nine commonly used rheological models were evaluated for their applicability to the two types of oil testing fluids. It was found that the Ross model was suitable for the potassium salt polymer system, while the power-law model was suitable for organic salt oil testing fluids. A new rheological parameter prediction model suitable for wide range of temperature and pressure and different testing fluid systems was proposed based on the optimized results. The average error for the potassium salt polymer system for oil testing fluids was 0.101%, and the error for the organic salt system for oil testing fluids was 0.113%. Both were superior to known rheological models and can meet the requirements of oil testing operations within the wide temperature and pressure range in the Bohai Bay Oilfield.

Inorganic salt-induced micellar morphologies in deep eutectic solvent: Structure and curcumin solubilization

Physico-spectroscopic data of deep eutectic solvent (DES, aquolines (choline chloride, ChCl: water (1:2 (DES I), 1:3 (DES II), 1:4 (DES III), and 1:5 (DES IV)) have been collected. The data differentiates DES I to DES III (DESs) from DES IV (molecular solution of ChCl). DESs (aquolines) are used to study association structures of surfactant + salt systems using spectrofluorometry, polarizing optical microscopy (POM), and dynamic light scattering (DLS). POM images show the formation of giant aggregates (vesicles, up to 3.3 µm) in DTAB – aquoline – salt system which was further confirmed using DLS. These systems show excessive solubility enhancement of the poorly water-soluble curcumin (CCM), a well-known natural drug and food ingredient. Solubility of CCM shows the following order: water < DES < DES + salt < DTAB-DESs < DTAB-salt-aquoline. CCM shows up to 250-fold solubility in DTAB-KNO3-DES I system compared to water. The work forging a new methodology of achieving giant amphiphilic aggregates and their application in improving the aqueous solubilities/extraction of hydrophobic materials.

Investigation of the Relationship between Molten Fluoride Salt Structure and Fluoroacidity Using Chromium As a Probe Redox Ion

Molten fluoride salts have been studied for decades due to their applications in the production of aluminum as well as in the operation of advanced nuclear reactors. Advanced fission and fusion nuclear reactor designs may include molten fluoride salts as coolants, fuel carriers (fission), or fuel breeding blankets (fusion). Relevant to their nuclear applications are the thermophysical and thermochemical properties of the salt. These include viscosity and thermal conductivity, as well as density, vapor pressure, and heat capacity. Underlying these properties are the interactions of the ions constituting the liquid, characterized by their coordination number, correlation times, and the possible formation of polymeric networks in the melt. The composition and structure of a melt, that is, what ions are present and how they interact, dictates the macroscopic properties relevant to reactor operation. Fluoroacidity, or the activity of dissociated fluoride anions, is one metric that may be used to describe the relationship between salt chemistry and structure. Overall, understanding the relationship between molten fluoride salt chemistry and structure enables deeper understanding and, thus, prediction of property changes that may take place throughout a reactor’s lifetime.In this poster, we present cyclic and square wave voltammetry studies of chromium speciation and diffusivity in various molten fluoride salts, connecting results with current understanding of the structure of the melts. Chromium is a thermodynamically favored corrosion product in molten salt systems, and in this study, it serves as a probe ion in different fluoride melts. Chromium trifluoride is added to various fluoride solvents and the diffusion coefficients of its various oxidation states are calculated and interpreted in light of salt structure. Experimental apparatus design and know-how for high-temperature molten salt electrochemistry are also highlighted.

Anion exchange membrane incorporating polymers of intrinsic microporosity for large organic anions

To meet a growing demand for the applications of electro-membrane technologies in the fields related to organic acid, this work attempts to incorporate polymers of intrinsic microporosity (PIM) with rigid and twisted structure into the preparation of anion exchange membrane (AEM) and investigates the possible effects of PIM addition on the transport behaviors of bulky organic anions therein. Firstly, molecular dynamics simulations are conducted to optimize the blend ratio between the modified PIM and chloromethylated Polysulfone. Furthermore, performances of as-prepared AEMs with different blend ratios are evaluated in some typical organic salt systems, including sodium lactate, sodium gluconate, and sodium citrate. Results demonstrate that water uptake increases and electrical resistance decreases significantly with increasing PIM loading despite the moderate reductions in ion exchange capacities. For example, a reduction of >50 % in electrical resistance when the PIM fraction increases up to 20 %. Small angle X-ray scattering reveals that these changes appear to be the result of micro-phase separation and increase of internal free volume. Additionally, electrometathesis-based organic acid conversion experiments confirm that the blend AEMs indeed contribute to reduce process energy consumption, for instance, a reduction of up to 23.29 % for the gluconic acid conversion. Although the addition of PIM results in a loss of membrane permselectivity to some extent, the corresponding current efficiency is still acceptable. Incorporation of Polymers of Intrinsic Microporosity is worth exploring for the preparation of Bulky Organic Anions-oriented AEM.

Nano-carbon octadecahedron: in situ carbonization of DTAB of aggregates in concentrated calcium chloride solution

Morphologies play an important role in carbon nanomaterials. Carbon nanomaterials with different morphologies have different applications in different fields. However, carbon nano-polyhedra have been rarely reported in literatures. Nano-carbon octadecahedron were prepared by the interaction of DTAB of aggregates with a concentrated solution of calcium chloride at 600 °C and with a size of about 700 nm. A series of characterizations, such as SEM, FT-IR, XPS, XRD, Raman, etc., proved that it conforms to the basic characteristics of carbon nanomaterials and may be doped with Ca and carbon. Successful preparation of carbon octadecahedron suggests that the use of in situ carbonization in a concentrated salt system is a new and worthwhile approach to explore.

Capsanthin-iodonium salt system for free radical photopolymerization under LED irradiation

The current photoinitiator (PI) is effective under mercury lamps but exhibits limited selectivity towards different radiation sources, which hinders its compatibility with eco-friendly LED lighting and raises concerns about toxicity and deep coloration. Capsanthin (Cap), with its strong photo-absorption in the 400–500 nm range, utilizes its conjugated structure to align the PI's absorption wavelength with the LED's emission spectrum. This study introduced Cap as a natural photosensitizer (PS) for free radical photopolymerization under LED irradiation. The Cap-based initiation system demonstrated promising photoinitiating capabilities under a 405 nm LED, achieving over 50 % double bond conversion in polymerized monomers. Furthermore, the system's photobleaching properties were exceptional, and its cytotoxicity was significantly lower than that of traditional PIs, such as benzoin methyl ether. The Cap's photochemical behavior under LED irradiation was explored, investigating its photoinitiating capacity and mechanism through fluorescence, photolysis, and electron paramagnetic resonance techniques. This research is vital for developing bio-based photoinitiating systems for photopolymerization in LED light environments.

Closed-Loop Direct Upcycling of Spent Ni-Rich Layered Cathodes into High-Voltage Cathode Materials.

Facing the resource and environmental pressures brought by the retiring wave of lithium-ion batteries (LIBs), direct recycling methods are considered to be the next generation's solution. However, the contradiction between limited battery life and the demand for rapidly iterating technology forces the direct recovery paradigm to shift toward "direct upcycling." Herein, a closed-loop direct upcycling strategy that converts waste current collector debris into dopants is proposed, and a highly inclusive eutectic molten salt system is utilized to repair structural defects in degraded polycrystalline LiNi0.83Co0.12Mn0.05O2 cathodes while achieving single-crystallization transformation and introducing Al/Cu dual-doping. Upcycled materials can effectively overcome the two key challenges at high voltages: strain accumulation and lattice oxygen evolution. It exhibits comprehensive electrochemical performance far superior to commercial materials at 4.6V, especially its fast charging capability at 15C, and an impressive 91.1% capacity retention after 200 cycles in a 1.2Ah pouch cell. Importantly, this approach demonstrates broad applicability to various spent layered cathodes, particularly showcasing its value in the recycling of mixed spent cathodes. This work effectively bridges the gap between waste management and material performance enhancement, offering a sustainable path for the recycling of spent LIBs and the production of next-generation high-voltage cathodes.

A Sodium Bis(fluorosulfonyl)imide (NaFSI)-based Multifunctional Electrolyte Stabilizes the Performance of NaNi1/3Fe1/3Mn1/3O2/hard Carbon Sodium-ion Batteries.

A sodium bis(fluorosulfonyl)imide (NaFSI)-based multifunctional electrolyte is developed by partially replacing NaPF6 salt in the electrolyte to improve the wide temperature range working capability of NaNi1/3Fe1/3Mn1/3O2/hard carbon (NNFM111/HC) sodium-ion batteries (SIBs). The capacity retention of the SIBs with NaFSI-NaPF6 dual salt electrolyte increases from 47.2 % to 75.5 % after 250 cycles at 25 °C, and from 51.0 % to 82.3 % after 80 cycles at 45 °C, and the 1 C discharge capacity retention at the low temperature of -20 °C also increases 26.8 %. In the single salt system, NaPF6 effectively passivate the aluminum foil and NaFSI passivate the electrode/electrolyte interface. The synergistic effect of NaPF6 and NaFSI greatly improves the battery performance in a wide temperature range. This NaFSI-based dual salt electrolyte also effectively overcomes the flaws when the SIBs using NaFSI or NaPF6 independently, and makes it more suitable for SIBs, indicating promising prospects in the commercial application of NNFM111/HC SIBs.

Forecasting state diagrams two-component salt systems

Forecasting state diagrams two-component salt systems

Advancing HIC method development: Retention-time modeling and tuning selectivity with ternary mobile-phase systems

The use of a ternary mobile-phase system comprising ammonium sulphate, sodium chloride, and phosphate buffer was explored to tune retention and enhance selectivity in hydrophobic interaction chromatography. The accuracy of the linear solvent-strength model to predict protein retention with the ternary mobile-phase system based on isocratic scouting runs is limited, as the extrapolated retention factor at aqueous buffer conditions (k0) cannot be reliably established. The Jandera retention model utilizing a salt concentration averaged retention factor (k¯0) in aqueous buffer for ternary systems overcomes this bottleneck. Gradient retention factors were derived based on isocratic scouting runs after numerical integration of the isocratic Jandera model, leading to retention-time prediction errors below 11 % for linear gradients. Furthermore, an analytical expression was formulated to predict HIC retention for both linear and segmented linear gradients, considering the linear solvent-strength (LSS) model within ternary salt systems, relying on a fixed k0. The approach involved conducting two gradient scouting runs for each of the two binary salt systems to determine model parameters. Retention-time prediction errors for linear gradients were below 12 % for lysozyme and 3 % for trypsinogen and α-chymotrypsinogen A. Finally, the analytical expression for a ternary mobile-phase system was used in combination with a genetic algorithm to tune the HIC selectivity. With an optimized segmented ternary gradient, a critical-pair separation for a mixture of 7 proteins was achieved within 15 min with retention-time prediction errors ranging between 0.7 and 15.7 %.

Thermodynamic behavior of CrF2 corrosion product in the molten LiF-ThF4 salt system

This work examines the thermochemistry of the chromium difluoride CrF2 corrosion product in the molten ▪ fuel salt system. Through a combination of experimental investigations and thermodynamic modeling assessment, the study elucidates the thermodynamic properties, phase diagram equilibria, and overall thermodynamic behavior of CrF2 corrosion product, following dissolution from a structural material to the molten salt fuel environment. In this work, two different synthesis methods were developed for pure CrF2, further allowing to experimentally measure the phase equilibria in the ▪ , ▪ , and ▪ systems. Then, thermodynamic models were developed using the CALPHAD method based on the quasichemical model in the quadruplet approximation.

Determining phase-transition temperatures of molten salt mixtures through microsecond-scale staircase voltammetry

Determining the phase-transition temperature is crucial in the design of molten salt reactors, as operational temperatures need to be established considering the safety margins related to the thermodynamic stability of the molten salt system. This study introduces a novel approach to determine the phase-transition temperature based on rapid electrical conductivity measurements using a microsecond-scale staircase voltammetry technique. The phase-transition temperature is determined near distinct points where the electrical conductivity abruptly changes, indicating phase transitions. The phase-transition temperatures of three LiCl–KCl molten salt systems, determined using the proposed approach based on electrical conductivity measurements, are with relative errors less than 3% compared with reported phase transition data based on conventional thermal analysis techniques.