Molten ZnCl2 Research Articles

Does Sn2+ play well with Zn2+ as their molten chloride salts react with Cr–Al–B MAB phase?

Novel Zn-MAX phases like Ti2ZnC were synthesized in the literature by the reaction between Lewis acid salts like ZnCl2 and the MAX phase. The interactions between the Cr–Al–B MAB phase contained in the PLS coating formed during HDA of Fe–Cr–B cast steel and five types of molten chloride salts (ZnCl2 and SnCl2) were investigated. The results showed that the Cr-(Al, Zn)–B and Cr-(Al, Sn)–B MAB phase solid solution were formed as the PLS coating reacted with the molten ZnCl2 and SnCl2, respectively, through topochemical reaction. Zn and Sn could not coexist in the A-site Cr–Al–B MAB phase solid solution, and the replacement ability of Sn2+ contained in molten salt was much stronger than that of Zn2+. Zn and Sn whiskers could spontaneously grow on the Cr-(Al, Zn)–B and Cr-(Al, Sn)–B MAB phase solid solution respectively.

Reaction Between Hot-Dip Aluminized Coating on Fe–Cr–B Cast Steel and Molten ZnCl2 Salt

Reaction Between Hot-Dip Aluminized Coating on Fe–Cr–B Cast Steel and Molten ZnCl2 Salt

Excellent lithium storage performance of bipyridinium-based polymerized ionic liquids as anode in lithium-ion batteries

For organic electrode materials, slow Li+ diffusion kinetics is a main obstacle to the realization of high lithium storage capacity through a super-lithiation reaction. Here, bipyridinium-based polymerized ionic liquids (PILs) have been synthesized by the ionothermal trimerization of 1,1-dicyanomethyl bipyridinium bromide ILs in molten ZnCl2 matrix, and are used as an anode material for the first time. In which, the ionic chains are beneficial for fast Li+ diffusion, as well as the p-π resonance structure between methylene and aromatic ring helps the electron conduction. Electrochemical analysis shows PILs-400 can deliver 1201.5 mAh g−1 at 0.1 A g−1 and almost no capacity loss with the capacity of 873.6 mAh g−1 over 500 cycles at 2 A g−1. Theoretical calculation reveals that all functional groups of triazine, methylene, and bipyridinium have taken part in the redox reaction, and this reaction is associated with a three-step insertion process of 19 Li+ for each repetitive unit in forming Li19C14N5, along with the reversible formation of N-Li and C-Li bonds.

Are High-Temperature Molten Salts Reactive with Excess Electrons? Case of ZnCl2.

New and exciting frontiers for the generation of safe and renewable energy have brought attention to molten inorganic salts of fluorides and chlorides. This is because high-temperature molten salts can act both as coolants and liquid fuel in next-generation nuclear reactors. Whereas research from a few decades ago suggests that salts are mostly unreactive to radiation, recent experiments hint at the fact that electrons generated in such extreme environments can react with the melt and form new species including nanoparticles. Our study probes the fate of an excess electron in molten ZnCl2 using first-principles molecular dynamics calculations. We find that on the time scale accessible to our study, an excess electron can be found in one of three states; the lowest-energy state can be characterized as a covalent Zn2Cl5•2- radical ion, the other two states are a solvated Zn•+ species (ZnCl3•2-) and a more delocalized species that still has some ZnCl3•2- character. Since for each of these, the singly occupied molecular orbital (SOMO) where the excess charge resides has a distinct and well-separated energy, the different species can in principle be characterized by their own electronic spectra. The study also sheds light onto what is commonly understood as the spectrum of a transient radical species which can be from the SOMO onto higher energy states or from the melt to pair with the excess electron leaving a hole in the liquid.

Enhancement of Methylene Blue Adsorption from ZnO/Activated Carbon Nanocompossites Prepared by Pyrolysis of Molten ZnCl2 with Rice Husks

In this work, we synthesized a facile step pyrolysis of ZnO/activated carbon nanocomposites by using molten ZnCl2 and rice husks in oxygen-limited environment. The mass ratio of molten ZnCl2 and rice husks was chosen from 0 to 5 wt.%, the pyrolysis temperature range from 400 to 800 oC. When the mass ratio of molten ZnCl2 and rice husks was equal to 1.0 and the pyrolysis temperature was at 800 oC, the size of ZnO nanoparticles in diameter was found to be of 10-20 nm. The ZnO/activated carbon nanocomposites exhibited a porous structure with the BET surface area, average pore diameter and pore volume of 643.9 m2/g, 4,76 nm and 0.255 cm3/g, respectively. To investigate the adsorption behavior of methylene blue, batch experiments were performed on all samples. The ZnO/activated carbon sample manufactured at a mass ratio of 1.0 and a pyrolysis temperature of 800 oC has the best methylene blue adsorption capability. The Langmuir isotherm was used to calculate the maximum adsorption capacity of methylene blue, which was 814.9 mg/g. Based on the obtained results, one can suggest that ZnO/activated carbon nanocomposites prepared by the facile pyrolysis route from molten ZnCl2 and rice husks possessing eco-friendly behaviour and low productioncost can be used as a potential adsorbent for wastewater treatment.

Refreshing the liquid-gas reaction interface to provoke the zincothermic reduction of SiCl4 to prepare lithium-storage nano silicon

Many heterogeneous reduction reactions are hampered by the generated intermediate products located at the interface of reactants, resulting in reducing the reaction area or slowing down the mass transfer and thereby shutting off or slowing down the reaction. Thus, removing the unwanted intermediate products from the reaction interface is key to enabling a rapid and sufficient reduction rate and rationally mediating the product sizes and structures. Herein, we employ solid NaCl to absorb the intermediate molten ZnCl2 generated at the liquid Zn-SiCl4 gas interface, making the reaction happen continuously and sufficiently at a relatively low temperature of below 450 °C. In addition to refreshing the reaction interface, NaCl acts as a buffer to absorb the reaction heat, ensuring the production of hollow Si inherited from the spherical liquid Zn template. As a result, the yield of Si reaches over 95% within 2 h and the Si particle size is below 200 nm. Further, the obtained Si anode has an initial Coulombic efficiency of 86.7% and delivers a capacity of 1580 mAh g−1 at 3 A g−1 after 350 cycles with a capacity retention of 90.6%. Overall, this paper provides an effective strategy for engineering the reaction interface and revalorizing waste SiCl4 for making Li-storage Si anodes.

N,S-Co-doping Significantly Improves the Co–Nx Content of the Co-NSPC Catalyst and Enhances the Catalytic Performance for Selective Hydrogenation of Halogenated Nitrobenzenes

Non-noble metals have attracted worldwide attention for the catalytic hydrogenation of halonitrobenzene due to their high activity, low price, and abundance on Earth. However, the construction of effective and stable non-noble-metal catalysts for the selective hydrogenation of halonitrobenzene to haloaniline by a simple method remains challenging. Herein, we report a facile one-pot method for the synthesis of N,S-co-doped mesoporous carbon-supported non-noble-metal catalysts through carbonization of a mixture of metallic precursors and 2-aminothiazole in molten ZnCl2. The prepared Co-NSPC catalyst showed excellent activity and selectivity with a turnover frequency of 84.4 h–1 in the hydrogenation of p-chloronitrobenzene to p-chloroaniline. Furthermore, Co–Nx was found to be the main active site for this reaction on the basis of characterization and experimental data, and the introduction of S promoted the formation of Co–Nx sites. Moreover, the Co-NSPC-800 catalyst can be reused at least four times and applied to the hydrogenation of 10 kinds of halogenated nitrobenzenes with excellent selectivity.

Electrochemical noise studies on localized corrosion of Ni and Ni-20Cr in molten ZnCl2

The electrochemical noise (ECN) technique was employed to study corrosion of two model systems, i.e. pure Ni and a binary Ni-20 wt%Cr (Ni20Cr) alloy in molten ZnCl2 at 623 K. We measured ECN transients in current and open-circuit potential from two nominally identical Ni-Ni and Ni20Cr-Ni20Cr electrodes and one galvanic Ni-Ni20Cr electrode pair. The behavior of ECN is quite distinct among the three-electrode systems, and it is correlated with the various microscopic observations of micro- and nano-scale morphological features. Based on the ECN study coupled with the microstructural analysis, the origins of ECN in the molten salt environment as well as the mechanisms of localized corrosion in the three systems are discussed.

Electrochemical removal of Cu, Fe and Mn from molten ZnCl2:KCl:NaCl

This study was carried out to investigate the use of electrodeposition for the removal of impurities from molten ZnCl2:KCl:NaCl in order to purify and reuse the molten salt after electrorefining and electrowinning. The deposition of the elements, Cu, Fe, and Mn from CuCl, FeCl2, FeCl3, and MnO2 in molten salt at 260℃ was examined using cyclic voltammetry (CV), employing graphite and platinum (Pt) electrodes. Subsequently, a series of potentiostatic electrolysis experiments were conducted to remove the impurities in the salt using a zinc (Zn) electrode. X-ray diffraction (XRD) was used in one case to analyze and confirm that the reduced element was deposited on the surface of the Zn electrode. The results show that Cu and Fe(III) were removed from the molten salt through 1.5 and 2.5 h of electrodeposition, respectively. The results for removing Fe(II) and Mn were slightly different after 3 h of purification, despite being mostly effectively separated, there were still some impurities found in the molten salt.

Covalent Triazine Frameworks and Porous Carbons: Perspective from an Azulene-Based Case.

Covalent triazine frameworks (CTFs) are among the most valuable frameworks owing to many fantastic properties. However, molten salt-involved preparation of CTFs at 400-600 °C causes debate on whether CTFs represent organic frameworks or carbon. Herein, new CTFs based on the 1,3-dicyanoazulene monomer (CTF-Azs) are synthesized using molten ZnCl2 at 400-600 °C. Chemical structure analysis reveals that the CTF-Az prepared at low temperature (400 °C) exhibits polymeric features, whereas those prepared at high temperatures (600 °C) exhibit typical carbon features. Even after being treated at even higher temperatures, the CTF-Azs retain their rich porosity, but the polymeric features vanish. Although structural de-conformation is a widely accepted outcome in polymer-to-carbon rearrangement processes, the study evaluates such processes in the context of CTF systems. A proof-of-concept study is performed, observing that the as-synthesized CTF-Azs exhibit promising performance as cathodes for Li- and K-ion batteries. Moreover, the as-prepared NPCs exhibit excellent catalytic oxygen reduction reaction (ORR) performance; hence, they can be used as air cathodes in Zn-air batteries. This study not only provides new building blocks for novel CTFs with controllable polymer/carbon features but also offers insights into the formation and structure transformation history of CTFs during thermal treatment.

Tuning the structure and electrochemical performance of pinecone-derived porous carbon for potassium-ion battery anodes using molten ZnCl2

Tuning the structure and electrochemical performance of pinecone-derived porous carbon for potassium-ion battery anodes using molten ZnCl2

Preparation of Porous Coke by Microwave Pyrolysis of Oily Sludge: Optimization Through Response Surface Methodology and TG-FTIR Analysis

Oily sludge (OS) is a kind of solid waste with precious oil resources in the petroleum industry. Because OS poses a severe threat to the environment, the treatment of OS has been widely studied. In this work, OS was used to prepare porous sludge coke a through microwave pyrolysis and one-step ZnCl2 activation technique. The response surface methodology was designed to optimize the parameters of the preparation process of porous sludge coke, and the interaction between the parameters was further analyzed. The experimental result showed that the model could fit the experimental results well. The optimal iodine adsorption value of porous sludge coke, 785.23 mg/g, was obtained by using the response surface methodology when the microwave power was 797 W, the ZnCl2 addition ratio was 0.5, and the pyrolysis time was 25 min. The experimental result showed that the model could fit the experimental results well. The influence of ZnCl2 on the pyrolysis of OS was investigated through TG-FTIR. The results showed that the presence of ZnCl2 could prevent the fracture of C-H bond, reduce the rate of carbon source loss caused by the fracture of long-chain hydrocarbons to produce short-chain hydrocarbons in OS, and enrich the carbon source of sludge coke. On the other hand, the molten ZnCl2 occupied the tiny pores when the oil components in the OS volatilized, which can enrich the pore volume of the sludge coke.

Ionothermal Synthesis of Covalent Triazine Frameworks in a NaCl-KCl-ZnCl2 Eutectic Salt for the Hydrogen Evolution Reaction.

Covalent triazine-based frameworks (CTFs) are typically produced by the salt-melt polycondensation of aromatic nitriles in the presence of ZnCl2 . In this reaction, molten ZnCl2 salt acts as both a solvent and Lewis acid catalyst. However, when cyclotrimerization takes place at temperatures above 300 °C, undesired carbonization occurs. In this study, an ionothermal synthesis method for CTF-based photocatalysts was developed using a ternary NaCl-KCl-ZnCl2 eutectic salt (ES) mixture with a melting point of approximately 200 °C. This temperature is lower than the melting point of pure ZnCl2 (318 °C), thus providing milder salt-melt conditions. These conditions facilitated the polycondensation process, while avoiding carbonization of the polymeric backbone. The resulting CTF-ES200 exhibited enhanced optical and electronic properties, and displayed remarkable photocatalytic performance in the hydrogen evolution reaction.

Ionothermal Synthesis of Covalent Triazine Frameworks in a NaCl‐KCl‐ZnCl2Eutectic Salt for the Hydrogen Evolution Reaction

AbstractCovalent triazine‐based frameworks (CTFs) are typically produced by the salt‐melt polycondensation of aromatic nitriles in the presence of ZnCl2. In this reaction, molten ZnCl2salt acts as both a solvent and Lewis acid catalyst. However, when cyclotrimerization takes place at temperatures above 300 °C, undesired carbonization occurs. In this study, an ionothermal synthesis method for CTF‐based photocatalysts was developed using a ternary NaCl‐KCl‐ZnCl2eutectic salt (ES) mixture with a melting point of approximately 200 °C. This temperature is lower than the melting point of pure ZnCl2(318 °C), thus providing milder salt‐melt conditions. These conditions facilitated the polycondensation process, while avoiding carbonization of the polymeric backbone. The resulting CTF‐ES200exhibited enhanced optical and electronic properties, and displayed remarkable photocatalytic performance in the hydrogen evolution reaction.

A perspective of ZnCl2 electrolytes: The physical and electrochemical properties

Molten ZnCl2 hydrates are ionic liquids at room temperature, which exhibit intriguing physical and electrochemical properties. Continuous efforts have been devoted over several decades to understanding the properties of the molten ZnCl2 hydrates that have been dubbed as water-in-salt electrolytes recently. The physical properties of molten ZnCl2 hydrates can be described from the perspectives of ions in their speciation and water molecules regarding their chemical environments. Recently, attention has been given to molten ZnCl2 hydrates as electrolytes for Zn metal batteries. It was revealed that the physical properties of such electrolytes have rich implications in their electrochemical properties. Therefore, it demands a holistic understanding of the physical and electrochemical properties of molten ZnCl2 hydrates to design functional electrolytes to serve high-performing Zn metal batteries. This perspective attempts to review the works that described the properties of concentrated ZnCl2 as an ionic liquid and as an emerging electrolyte. The author also provides a perspective to highlight the needs of future research to circumvent the limits of this electrolyte.

Superlithiation Performance of Covalent Triazine Frameworks as Anodes in Lithium-Ion Batteries

Organics with the merit of renewability have been viewed as the promising alternative of inorganic electrode materials in lithium-ion batteries, but most of them display inferior performance due to the sluggish ion/electron diffusion and the potential dissolution in aprotic electrolytes. Here, covalent triazine frameworks (CTFs-1), full of vertical pores and layered spaces for Li+ transfer, have been synthesized with p-dicyanobenzene as the monomer by a facile two-step method including a prepolymerization with CF3SO3H as the catalyst and deep polymerization in molten ZnCl2. CTFs-1-400, obtained at the deep polymerization temperature of 400 °C, exhibits the superlithiation property with the specific capacities of 1626 mA h g-1 at 25 °C and 1913 mA h g-1 at 45 °C at 100 mA g-1, indicating the formation of Li6C6/Li6C3N3 in the reduction process. Electrochemical analysis and density functional theory calculation indicate that the ultrahigh capacity is mainly contributed by the capacitance of micropores and the redox capacity of benzene and triazine rings. Moreover, CTFs-1-400 displays the specific capacity of 740 mA h g-1 for 1000 cycles at 1 A g-1 with almost no capacity fading.

Direct synthesis of hierarchical porous polymer nanoparticles from nitrile monomers and its application for methylene blue adsorption

Microporous covalent triazine-based frameworks (CTFs) have been widely used as adsorbents, separation and catalysts in the past few years, but the confined microporous network often induces diffusion limitations of molecules to and from the active sites. Here, we present a general bottom-up synthetic strategy to produce hierarchical porous polymer nanoparticles by cyclotrimerization of 1,4-dicyanobenzene in molten ZnCl2. Controlling the ratio of monomer to molten salts is the key to prepare hierarchical porous polymer nanoparticles by ionothermal methods, and uniform nanoparticles with particle size of 100–400 nm can be facilely synthesized at a low monomer/ZnCl2 molar ratios. The resulting hierarchical porous polymer nanoparticles exhibit great adsorption capacity of methylene blue. The enhancement is ascribed to enhanced mass transfer of the molecules and easy access to the active sites as a result of the short diffusion lengths of hierarchical porous polymer nanoparticles. This method is simple and efficient for the preparation of size-controllable hierarchical porous polymer nanoparticles from nitrile monomers, which is conducive to expand its application in adsorption, catalysis and other related fields.

Determining oxidation states of transition metals in molten salt corrosion using electron energy loss spectroscopy

This work utilizes electron energy loss spectroscopy (EELS) to identify oxidation state of alloying elements in Ni-based alloys after exposure to molten chloride salt systems. Pure Ni and Ni-20Cr model alloy were corroded in molten ZnCl2 and KCl-MgCl2 under argon atmosphere at various temperatures. Oxidation states of Cr (Cr3+) and Ni (Ni2+) in the molten salt after corrosion were determined by monitoring changes in the L2,3 edges of corresponding EELS spectra. Oxidation state mapping technique using principal component analysis and multiple linear least squares fitting in HyperSpy Python package was developed.

Investigating the Effect of CrCl3 on Corrosion Behavior of Ni and Ni-20Cr in Molten ZnCl2 Salt By Electrochemical Noise Measurements

Molten chloride and fluoride salts possess various properties such as good thermal conductivity and stability, large specific heat and low viscosity which make them important as fuels and/or coolants for molten salt reactors (MSR). Molten chloride salts are also selected as heat transfer and storage fluids to carry thermal energy from a solar concentrator to a steam generator in concentrating solar power (CSP) technologies. In both the applications the nickel-based alloys are used as structural materials. However high operating temperatures and extremely corrosive nature of molten salts promote faster corrosion of the structural materials. Hence, the corrosion behavior of the structural materials needs to be understood and monitored with time when exposed to the corrosive molten salt environment. Electrochemical techniques are useful for understanding the corrosion mechanism of metals and alloys in molten salts. Among them, electrochemical noise (ECN) is a simple in-situ technique to monitor the corrosion in real time without applying any external signals to the metal/alloy in corrosive environments. A unique advantage of ECN technique is the possibility to detect and analyze the early stages of the localized corrosion process during corrosion initiation as well as a type of corrosion.The corrosion of metals and alloys in molten chloride is strongly affected by impurities (O2, H2O) present in the atmosphere, temperature changes, and concentrations of various chemical impurities (metal oxides and metal chlorides). These impurities have been considered as strong oxidizing agents for metals and alloys in molten chloride salts. Chromium is a major alloying element in nickel-based alloys. Cr can be oxidized into metal chlorides CrClx (x=2,3) due to their favorable Gibbs free energies of the formation as compared to NiCl2 at 623 K. Cr3+ and Cr2+ coexist in the molten salt during corrosion of nickel-based alloys, while Cr3+ is the primary valence state. It is important to study the effect of these multi-valent ions on corrosion of metals/alloys in molten salts. To the best of our knowledge, no study on the effect of Cr3+ on the metals/alloys in molten chloride medium has been reported.The effect of CrCl3 on the corrosion behaviour of Ni and Ni-20 wt %Cr (NiCr) alloy in purified molten ZnCl2 at 623 K was investigated for the first time using ECN measurements in an argon-filled glovebox. ECN measurements were carried out in a three-electrode setup using two working electrodes and platinum as a reference electrode in molten CrCl3-ZnCl2 at 623 K. Ni and NiCr corrosion behavior was examined in two different combinations : 1) identically coupled electrodes (Ni-Ni and NiCr-NiCr vs Pt) and 2) galvanically coupled electrodes (Ni-NiCr vs Pt). Different types of current and potential noise fluctuations have been identified for pitting and other forms of corrosion. Analysis of fluctuations in current and potential noise in Ni and NiCr in all the three combinations concluded that Ni and NiCr exhibited localized corrosion. The addition of CrCl3 to ZnCl2 accelerated the dissolution of Cr and Ni at the metal-salt interface. After ECN studies, the working electrodes were examined by scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS). STEM/EDS/EELS observations confirmed pit formation, Ni and Cr dissolution, and Cr depletion at the salt-metal interfaces. Ni-rich and Cr-depleted precipitates were observed in the salt with a galvanically coupled NiCr electrode after ECN studies. The in-depth ECN results will be discussed in conjunction with micro- and nano-scale imaging of dissolution of Ni and Cr elements at the metal-salt interface, and plausible corrosion mechanisms will be proposed. The present ECN results on Ni and NiCr are compared with ECN studies in pure ZnCl2 salt.This work was supported as part of the Molten Salts in Extreme Environments Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science.

Investigating corrosion behavior of Ni and Ni-20Cr in molten ZnCl2

Corrosion of Ni and Ni-20Cr in molten ZnCl2 under argon atmosphere at 593 K was investigated using cyclic polarization in combination with various electron microscopy techniques. Cyclic polarization measurements yielded significantly lower corrosion rates for pure Ni than for Ni-20Cr. Corrosion of the Ni-20Cr alloy is attributed to selective anodic dissolution of Cr, which forms a chromium chloride film at the metal-salt interface. The corrosion in Ni and Ni-20Cr is accelerated by grain boundary attack through intergranular corrosion, followed by the formation of pore-salt network regions. The related corrosion mechanisms and dissolution kinetics are discussed.