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• Power networks can use inexpensive liquid metal batteries for large-scale energy storage. • Liquid metal batteries' special structure can prevent dendritic development and minimize safety risks. • The study of liquid metal electrolytes is less than that of liquid electrodes, hence the focus must be shifted to electrolyte research. • Liquid metal batteries' electrolyte issue must be resolved for them to function in low-temperature conditions. Liquid metal batteries possess stable safety performance, high rate performance, and thermal stability. The liquid metal battery stores a large amount of electrical energy producing from wind energy or solar energy. The remarkable performance of the liquid metal batteries is partly attributed to electrolyte, which is an important component of the battery. In this paper, the important research progress of liquid metal batteries electrolyte are reviewed and the electrolyte types which have an influence on energy efficiency are discussed in detail. Then, the limitations and challenges of existing electrolytes are also pointed out. On this basis, the key development directions of liquid metal electrolytes are discussed and clarified. [Display omitted] [ABSTRACT FROM AUTHOR]

• The electrochemical behavior of molybdenum ions and their electrodeposition mechanism in molten salts were systematically investigated. • The variation of Mo element concentration and the valence state of the molten salt bottom product was tested by in situ salt extraction during electrolysis. • The causes of current fluctuation during constant voltage electrolysis were revealed, culminating in the successful electrolysis of molybdenum. The electrochemical behaviors of molybdenum ions in NaCl-KCl molten salt at 750 °C were studied in detail, and pure metallic molybdenum was collected on the cathode. The reduction and diffusion processes of molybdenum ions in NaCl-KCl molten salt were also identified using cyclic voltammetry and square wave voltammetry. The diffusion coefficient and nucleation mode of molybdenum ions were analyzed. Electrodeposition was performed at a constant voltage and the variation of current with time was recorded. The variation of Mo element concentration and the valence state of the molten salt bottom product was tested by in situ salt extraction during electrolysis. The result demonstrated that the electrode reduction process of molybdenum ion in NaCl-KCl molten salt at 750 °C was a two-step reaction, Mo(V) → Mo(III) → Mo, all of which was reversible and controlled by diffusion. Meanwhile, the nucleation mode of molybdenum ions was found to be progressive nucleation. It was determined by XRD, SEM and EDS that the primary component of the cathode deposition product was molybdenum. [ABSTRACT FROM AUTHOR]

• Shape-controlled synthesis of W particles via salt-assisted reduction was proposed. • Large powders disappeared and were degraded under the influence of Y(NO 3) 3. • Temperature and additive greatly affected the morphology and size of W particles. • The added salt improved the crystallization of particles. • The reaction mechanism was discussed as well. Tungsten, one of the refractory metals, has lots of excellent properties, making tungsten powders become a choice of raw material for many applications. This work reported a simple method (the salt-assisted hydrogen reduction of WO 3 powders) for preparing tungsten powders with desired morphologies and size. By adjusting the amount of additive (Y(NO 3) 3) and reduction temperature, metallic tungsten particles with different morphologies and size were obtained. It was found that both temperature and additive had apparent effects on the morphology and size of metallic W particles, and the large parallelepiped-shaped powders disappeared and large irregular blocky-shaped powders were degraded under the influence of additive. With the increase of temperature and amount of salt, particles became more dispersed and the size increased at higher temperatures, and the shape of particles was changed from spherical to polyhedral as well. On the contrary, the size of sub-particles became smaller as increasing amount of Y(NO 3) 3 at lower temperatures. Based on the results, the reaction and refining mechanisms for preparing tungsten were proposed as well. [ABSTRACT FROM AUTHOR]

In recent years, MOF-based materials, including pristine metal-organic frameworks (MOFs) and their derivatives, are one kind of the most popular materials, and have been widely used in biomedicine, sensing, energy storage, and catalysis due to their unique pore structures, abundantly accessible metal nodes, large specific surface areas, tailorable function, and morphology. Most of them have shown satisfactory performances in specific fields. However, there are still some urgent problems need to be solved in the application of MOF-based materials in electrocatalytic water splitting, especially the facile and controllable synthesis, and limited activity and stability. Herein, first this article mainly reviewed the applications and challenges of MOF-based materials in electrocatalytic water splitting. Then, typical development strategies (e.g., construction of multi-metallic site of MOF-based materials, structural morphology designing and controlling, engineering of doping, defect, vacancy, coupling with conductive carrier or constructing heterostructures) were highlighted in this review. Finally, perspectives on the development of MOF-based materials were provided for fabricating more efficient water splitting electrocatalysts. [Display omitted] • Different strategies to enhance the electrocatalytic performances of MOF-based materials are summarized. • Advantages of MOF-based materials in electrochemical water splitting are summarized. • The mechanisms of the enhanced catalytic activity are explored. • Some challenges and views for the future development of MOF-based materials are highlighted. [ABSTRACT FROM AUTHOR]

MXenes are a recently discovered family of two-dimensional (2D) early-transition metal carbides and carbonitrides that have already shown many attractive properties and great promise in energy storage and other applications. Although many MXenes have been synthesized, most MXenes contain only one or two transition metals. The preparation of medium-entropy or high-entropy MXenes is an important and challenging task due to the excellent properties resulting from increased configurational entropy. Herein, new three-transition-metal MAX phases, Ti 2 V 1−y Cr y AlC 2 , and the corresponding MXenes were synthesized successfully for the first time. By combining aberration-corrected scanning transmission electron microscopy (AC-STEM), density functional theory (DFT) and synchrotron X-ray pair distribution functions (PDF) analyses, we determined the structure of Ti 2 V 0.9 Cr 0.1 C 2 T x , which exhibits a Ti-V-Cr solid solution in the three atomic layers. Furthermore, when applying these MXenes as the electrode of a supercapacitor, the single-layer Ti 2 V 0.9 Cr 0.1 C 2 T x shows a remarkable gravimetric capacitance (553.27 F g−1 at 2 mV s−1). This work not only expands the family of MXenes, but also provides a strategy to prepare medium-entropy and high-entropy MXenes. [Display omitted] We successfully synthesized and characterized the three-transition-metal Ti 2 V 1−y Cr y AlC 2 MAX phases (y = 0.1, 0.25, 0.5) and accordion-like Ti 2 V 0.9 Cr 0.1 C 2 T x MXenes, for the first time. By combining DFT, X-ray PDF and ac-STEM characterization, the structure of Ti 2 V 0.9 Cr 0.1 C 2 T x was determined. Besides, Ti 2 V 0.9 Cr 0.1 C 2 T x exhibited good gravimetric capacitance (553.27 F g−1 at 2 mV s−1) in a three-electrode system. • The new three-transition-metal Ti 2 V 0.9 Cr 0.1 C 2 T x MXene are synthesized and characterized. • By combining DFT, X-ray PDF and ac-STEM characterization, the structure of Ti 2 V 0.9 Cr 0.1 C 2 T x is determined. • Ti 2 V 0.9 Cr 0.1 C 2 T x exhibits good gravimetric capacitance (553.27 F g−1 at 2 mV s−1) in a three-electrode system. [ABSTRACT FROM AUTHOR]

Titanium oxycarbide can be used as a soluble anode to produce sponge titanium in USTB or MER molten salt electrolysis process. However, the key factor of these two processes is to prepare oxycarbide with appropriate C/O ratio and at a low cost as well. This work reported a simple method of preparing titanium oxycarbide from TiO 2 in C-H 2 system. Based on the prediction of thermodynamic calculations, titanium oxycarbide was prepared successfully at 1400 °C with the molar ratio of TiO 2 to carbon exceeding 1:2, and the ideal electrolytic anode (TiC 0.5 O 0.5) was produced at 1400 °C (with a ratio of 1:3 of TiO 2 to carbon). Number of parameters (carbon content, temperature, sample's mass, additive (Fe element), and with ball milling treatment) were considered and discussed in the current study. Furthermore, this method can reduce not only the reaction temperature and time, but also the emission of carbon dioxide. • Titanium Oxycarbide with controllable C/O ratio was produced by considering number of parameters in TiO 2 -C-H 2 System. • The ideal electrolytic anode (TiC 0.5 O 0.5) can be produced when the ratio of TiO 2 to carbon is 1:3 at 1400 °C. • The reaction temperature, the usage and emission of carbon were reduced by introducing clean energy (H 2). • The reaction mechanism was discussed as well. [ABSTRACT FROM AUTHOR]

Abstract The reduction of metal oxides by hydrogen is a very significant reaction in metallurgical industries. Particularly, hydrogen reduction is one of the effective methods to reduce CO 2 emission in iron and steel industry. The mathematical modeling of H 2 reduction process would help to define the operating parameters and to get a better control of the reduction process. In this study, a new kinetic model regarding hydrogen reduction of metal oxides controlled by external gas diffusion has been proposed. The model has incorporated numbers of parameters such as temperature, size of the metal oxides, diffusion coefficient constant, hydrogen partial pressure, density of metal oxides and time. Furthermore, the shape of metal oxides (spherical, cylindrical, lamellar particles) was considered as well, and the models for the reduction of metal oxides with different shapes were combined to a formula. Also, the developed model can be applied to describe the reduction kinetics under both isothermal and non-isothermal conditions. Because the model is in the analytic function, therefore, it is convenient for usage and theoretical analysis. Application of the developed model to practical systems validated that its predicted values agreed very well with the experimental data. Highlights • Kinetic model for the external gas diffusion controlling reduction was proposed. • The model is in the analytic function and is convenient for theoretical analysis. • The shape of metal oxides was considered. • The models for different shapes were combined to a formula. [ABSTRACT FROM AUTHOR]

In the present study, a new and simple method to prepare tungsten and tungsten carbides powders was proposed by using WO 3 powders as the raw material and CH 3 OH vapor as the reduction and carbonization agent. Both thermodynamic and experimental studies were carried out, and based on the results, the reaction routes were obtained. It was found that at low and moderate temperatures, the final product of WC was formed via intermediates of W 18 O 49 , WO 2 , partial metallic W and W 2 C; while at high temperature, WO 3 was first reduced to WO 2 with the intermediate phase of W 18 O 49 , and then reduced to W. The morphology of final products almost retained the same shape as that of raw materials WO 3 at low temperature, however, the large particles with blocky shape disappeared and the products were all small W particles with polyhedral shape at high temperature. Furthermore, the reaction mechanisms were proposed: the pseudomorphic transformation mechanism dominated the reaction at low temperature, but at high temperature, the reduction obeyed the chemical vapor transport mechanism, which is beneficial for grain refining of final product. [ABSTRACT FROM AUTHOR]

• It is a novel process for the separation and preparation of molybdenum and zinc from MoS 2 and ZnS in magnetic separation tailings. • The electrochemical behaviors of MoS 2 , ZnS and MoS 2 -ZnS was investigated in detail, and the mechanism of desulfurization of MoS 2 -ZnS was proposed. • Zn/ZnS played a role of a reducing agent in the process of MoS 2 -ZnS co-desulfurization, which facilitated the process of desulfurization and the semiproduct of zinc could be reused. • It enabled the reduction of MoS 2 at a lower voltage while ZnS presenting in the desulfurization process. The main form of molybdenum in nature is molybdenum sulfide. It also exists in iron ore magnetic separation tailings together with zinc sulfide. Considering separating and extracting molybdenum and zinc, a large amount of SO 2 is released and environmental pollution is caused by high energy consumption for the traditional pyrometallurgy process. This research proposes a novel process to achieve efficient extraction and separation of molybdenum and zinc through co-desulfurization of MoS 2 -ZnS in molten salt. It was found that the sulfur in MoS 2 and ZnS could be effectively removed and collected as solid sulfur by constant potential electrolysis in molten NaCl-KCl at 750 °C. Furthermore, electrochemical testing showed that the decomposition of MoS 2 was carried out in two steps, ZnS was reduced in one step, and the decomposition voltage of ZnS was smaller than that of MoS 2. Zinc was obtained at the first stage, and the MoS 2 or its intermediate compounds were wrapped around by liquid zinc. The substitution reaction, 2Zn + MoS 2 = Mo + 2ZnS, was able to promote the decomposition of MoS 2 in the electrolysis process. Zinc sulfide was then formed in the second stage, and it can be electrolyzed to metallic zinc again for reduction of MoS 2. Zn/ZnS played the role of a reducing agent in the process of MoS 2 -ZnS co-desulfurization, which facilitated the process of desulfurization, and enabled the reduction of MoS 2 at a smaller voltage while zinc could be reused. In this work, molybdenum metal containing zinc was extracted at a cell voltage of 2.7 V. Metallic zinc and molybdenum were separated and purified in the final stage by vacuum distillation. [ABSTRACT FROM AUTHOR]

A review emphasized on the electro-desulfurization mechanism of sulfides as cathodes or anodes in molten salts. [Display omitted] • The research advance of metal or alloy prepared by molten salt electro-desulfurization is reviewed for the first time in this paper. • This review provides a comprehensive insight into the electrode reaction mechanism of various metal sulphides in molten salts. • The challenges in molten salt electro-desulfurization technology are summarized and the future research direction is pointed out. Sulfide is one of the most abundant minerals in the earth's crust and a major raw material for metal extraction. The traditional pyrometallurgy or hydrometallurgy process is relatively lengthy, and will produce CO 2 and SO 2 with greater hazards for environment. Electro-desulfurization is a metal extraction method developed in the past 20 to 30 years, which is considered to be an environmentally friendly and simple process. In electro-desulfurization process, sulfide is used as electrode and raw material, and molten salt is used as electrolyte. Metal and elemental sulfur are extracted at the cathode and anode respectively after current is introduced, meanwhile CO 2 and SO 2 are not produced. In this paper, the recent research of electro-desulfurization in molten salts is summarized, including the electrode reaction process when sulfide is used as cathode or anode, electrolytic products and factors affecting current efficiency and energy consumption. It is expected to provide suggestions for future direction and enhance the theoretical support for the clean development of sulfides through the comprehensive analysis of molten salt electro-desulfurization process. [ABSTRACT FROM AUTHOR]

Tungsten carbides, which can be widely used as cutting and drilling tools, chemical catalysts and aerospace coatings, have attracted widespread attentions. The present work reported a simple method to prepare tungsten carbides by using WO 2 as the raw materials and CO as the reduction and carbonization agent. It was found that at lower and moderate temperatures, all the final product was WC, while at higher temperatures, the final products were W 2 C or W. The reduction and carbonization mechanism was also studied theoretically and experimentally. WO 2 was reduced and carburized to WC in one step at lower temperatures; WO 2 was first reduced and carburized to W 2 C and then to WC at moderate temperatures; while at higher temperatures, WO 2 was first reduced to metallic W and then carbonized to WC or W 2 C, but with the temperature increasing, the carbonization became difficult and required much higher CO content. [ABSTRACT FROM AUTHOR]

• A novel process for extraction titanium from high Ti-BF slag has been proposed. • The effects of Fe 2 O 3 , urea and sawdust additives on the reaction have been studied. • The proposed novel recycling process has been assessed. • The novel recycling process showed many potential advantages and great feasibility. The recycling of high-titanium-bearing blast furnace slag (TiO 2 > 23 wt.%) is an urgent problem that has attracted global research attention. To achieve high-efficiency, low-consumption, clean, and high value-added recycling utilization, a new process is proposed herein, which entails reacting a CH 4 -H 2 -N 2 gas mixture with the titanium-bearing blast furnace slag to initially produce Ti(C, N, O) at a low temperature, whereafter the product is purified and chlorinated. The effects of Fe 2 O 3 , urea, and sawdust on the reduction and carbonitriding characteristics are also investigated. The results indicate that the Fe 2 O 3 additive can promote the formation of Ti(C, N, O), while urea and sawdust are instrumental for enhancing gas diffusion in solid powders. The proposed novel recycling process was assessed and it evinced many advantages and great feasibility. [ABSTRACT FROM AUTHOR]

The present study investigated the reduction and carbonization behavior of perovskite-geikielite by using CH 4 –H 2 gas mixture, which aimed to recycle the titanium resource in titanium-bearing blast furnace slag. Thermodynamic phase equilibrium analysis in the CaTiO 3 –CH 4 –H 2 , MgTiO 3 –CH 4 –H 2 and CaTiO 3 –MgTiO 3 –CH 4 –H 2 systems was performed by FactSage. The analysis indicated that CaTiO 3 could be ultimately reduced and carbonized to TiC x O y by CH 4 –H 2 gas mixture at temperature above 1300 °C, while the temperature for reduction of MgTiO 3 was above 1200 °C. MgTiO 3 is found to be reduced prior to CaTiO 3 in the CaTiO 3 –MgTiO 3 –CH 4 –H 2 systems. The reduction experiments of perovskite-geikielite were carried out in a temperature range of 1300 °C to 1450 °C in a flowing CH 4 –H 2 atmosphere. Experimental results showed that perovskite-geikielite could be reduced completely to TiC x O y at 1400 °C and above after 8 h reduction, while geikielite was reduced prior to perovskite. The reduction and carbonization extent of samples increased with increasing time and temperature when in a low temperature range (below 1400 °C). However, a much higher temperature (above 1400 °C) would hinder further carbonization of TiC x O y for the production of deposited carbon. Addition of iron oxides to sample strongly facilitated the reduction reaction, and even promoted the reduction of titanium to be completed at only 1300 °C after 8 h reduction. The gas-solid reaction provided a low temperature method to reduce and carbonize perovskite and geikielite, and thus it provided a possible way to use titanium-bearing blast furnace slag. Unlabelled Image • A novel method to reduce and carbonize perovskite and geikielite was proposed. • Thermodynamic and experimental study on the reduction by CH 4 -H 2 was performed. • The ratio of TiC/TiO in TiC x O y reduced from CaTiO 3 and MgTiO 3 has been estimated. • The reduction mechanism of gas-solid reaction with CH 4 -H 2 was discussed. [ABSTRACT FROM AUTHOR]