Formation Of Solid Solution Research Articles

Microwave-Assisted Synthesis of Platinum-free High-Entropy Alloy Catalysts on Reduced Graphene Oxide Sheets for Enhanced Oxygen Reduction and Evolution Reactions.

Nano-sized high-entropy materials (HEMs) recently received more attention to researchers due to their superior electrochemical catalytic properties. HEMs comprise at least five elements with or without metals and are synthesized through solid-state reactions and solution-mediated techniques. The presence of many elements in these HEMs result in a high mixing entropy and facilitates the formation of stable solid solutions in fundamental crystal structures. Herein, Pt-free high-entropy alloys (HEAs) were synthesized through facile and straightforward pulse microwave (PM) synthesis technique, which serve as efficient electrochemical catalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The PM synthesis method was conducted at an extremely low temperature (100 °C) without any external catalytic reagents. Using this PM technique, Cr18.2Zr13.5Ti5.3Co17.8Ni8.4Cu8.5Fe28.3 and Al15.3Mn18.2Ti3.7Co23.2Ni5.9Cu5.9Fe27.8 HEAs catalysts were synthesized with superior catalytic activity towards OER and ORR and compare its activities with pure Pt catalysts. The as-prepared HEAs also display an anti-CO poisoning effect and long-term durability, as compared to pure Pt catalysts. The low-temperature PM approach not only confirms the feasibility of synthesis of noble metal-free HEAs but also validates their superior catalytic activity towards OER and ORR, which is beneficial for the development of proton exchange membrane fuel cells and proton exchange membrane water electrolysis.

Progress in the development of NiO/MgO solid solution catalysts: A review

NiO/MgO solid solution materials have emerged as highly effective catalysts for various catalytic processes, including dry methane reforming, CO2 hydrogenation, methane partial oxidation, and steam reforming of hydrocarbons. The similar lattice parameters of NiO and MgO allow the formation of homogeneous solid solutions, where metallic Ni particles can be generated through the NiO reduction that is controlled by MgO isolation effect on NiO in the solid solution. The small size of these particles plays a crucial role in preventing carbon deposition and sintering in catalytic reactions. In this review, the basic principles of the formation of NiO/MgO solid solution, the reduction properties of the catalysts, and the insight into its high catalytic activity are elucidated. The synthesis methods of NiO/MgO solid solutions are presented. In addition, the recent progress of catalytic applications of NiO/MgO solid solutions is provided.

Analysis of Technologies for Applying High-Entropy Coatings by Physical Deposition Method

Introduction. Modern tribology solves the problems of increasing the reliability of friction units through applying vacuum wear-resistant coatings by the physical vapor deposition (PVD) method. More than five thousand scientific papers are devoted to high-entropy alloys (HEA). However, an urgent question about the possibility of obtaining wear-resistant and antifriction high-entropy coatings (HEC) using the PVD method remains unsolved. Its solution opens up the possibility of using HEC in mechanical engineering. The presented article is intended to fill this gap. Research objectives are as follows: to identify the key results on the creation of HEC by such PVD methods as vacuum arc evaporation and magnetron sputtering, to establish tribological characteristics of PVD coatings.Materials and Methods. From November 2023 to February 2024, the authors analyzed materials published in the Web of Science, Elibrary, Scopus, Medline, CINAHL databases in the Russian and English languages.Results. At the first stage, the literature on the vacuum arc coating method was considered. The issues of creating a vacuum arc discharge, its technological features, disadvantages, as well as processes in the cathode region of the arc were studied. The conditions of existence of cathode spots, the influence of temperature on the erosion coefficient, and processes on the anode and substrate were noted. The dependence of the deposition rate on the value of the potential on the substrate was shown. Nitride and combined coatings obtained by vacuum-arc method were analyzed: TiN, TiCN, TiAlN, TiMoS, TiSiN, TiN/VN, TiAlN/DLC-Ti. At the second stage, the history of the magnetron sputtering method was presented; technological features, types of magnetrons and nitride coatings obtained in this way were described. The third stage was devoted to the five-stage process of forming the coating structure. Island, layer-by-layer, and mixed growth modes of coating were considered. A schematic representation of the fundamental processes of structure formation was given. Defects in vacuum coatings were noted. At the fourth stage, the HEC based on the HEA were presented. Parameters predicting the formation of a HEA solid solution were indicated. Six families of high-entropy alloys were considered. Modern high-entropy coatings obtained by vacuum arc and magnetron methods were evaluated. The results of studies of structural-phase and physico-mechanical properties were summarized in the form of a table. The data of tribological studies of high-entropy coatings were presented.Discussion and Conclusion. The literature on HEC describes the coating structure, physical and mechanical properties, and thermal stability. The authors of the presented article found a gap in the research of tribology of high-entropy coatings. From the known results, it can be concluded that these coatings are frictional. However, due to their high hardness and ductility, they exhibit high wear resistance. In addition, it is difficult to talk about their tribological purpose. To solve the issue of the possibility of using PVD coatings in mechanical engineering, attention should be paid to the development of compositions with high hardness, wear resistance, and low coefficient of friction. They can be operated in tribo-loaded nodes.

Assessment of the durability of hardening products of modified fly ash cement compositions

This work is devoted to the study of the durability of hardening products of modified gold-cement compositions. The influence of sulfate and carbonate additives of various origins on the kinetics of increasing the strength of artificialstone was studied.To reveal the mechanism of the processes of strength synthesis of the developed binder systems, their hydration products and the composition of new formations were studied using X-ray diffraction (XRD), differential thermal analysis(DTA) and electron microscopy.It was established that with simultaneous modification of the plasticized fly ash cement composition with sulfate and carbonate additives, the synthesis of strength is ensured due to the formation of hydration products in the composition atthe early stages of hardening of ettringite and its analogues containing carbonate and ferric components. It has been determined that the presence of hydrosulfoaluminate-type new formations in the hydration products and the presence of active mineral additives in its composition on the one hand, and on the other hand, the contact of cement stonewith the environment can cause the appearance of dangerous compounds (such as thaumasite) in hardening systems, the synthesis of which leads to the emergence of stresses in the structure of the material and its destruction. It has been established that as a result of the processes of isomorphic substitution, compounds of variable composition are formed, similar to solid solutions, due to which the strength of artificial stone is ensured in the later stages of hardening. On the other hand, the released sulfate ions can replace silicon groups in the tobermorite gel and form compounds similar to epistilbite (Ca6(Si(OH)6)3·(SO4)3·24H2O) (d=0.584; 0.399; 0.369; 0.354 nm). The strength indicators of artificial stone basedon modified fly ash cement binder compositions were investigated. It is associated with the directed formation of crystallochemically similar phases that can grow together, and the formation of artificial stone capable of structural and functional adaptation in various operating conditions will likely be due to the formation of solid solutions of hydrosulfoaluminocarbosilicate composition, hydrogarnet phases of the composition 3СаО·Al2O3·1,6SiO2·2,8H2O and modified calcium hydrosilicates of the epistilbite type Ca6(Si(OH)6)3·(SO4)3·24H2O) and scoutite (Са6Si6O18·2H2O·CaCO3). in the composition of new formations.

A first-principles investigation on the enthalpy landscape for the hibonite solid solution: Implications for a nebular barometer

Abstract Hibonite, nominally CaAl12O19, is among the first minerals thermodynamically predicted to have formed in the early history of our solar system. It can incorporate significant amounts of Ti (≤15 wt%, ∼2 cations per formula unit) into its crystal structure as both Ti4+ and Ti3+. The main pathways for Ti incorporation in the solar nebula include a direct substitution of Ti3+ replacing Al3+ and a coupled substitution in which Ti4+ and Mg2+ replace two Al3+. Additionally, the formation of oxygen vacancies can also reduce a Ti4+ cation to Ti3+ by trapping a free electron. The relative amounts of these cations potentially reflect the fugacity of oxygen (fO2), a fundamental thermodynamic parameter, that prevailed when hibonite first formed or last equilibrated. However, the Ti content and its oxidation state in hibonite does not depend solely on fO2. The composition of the system is, thus, a key factor in changing the Ti4+/ΣTi ratio of the structure concurrently with the fO2. Therefore, it is necessary to understand the energetics, complex crystal chemistry, and substitution reactions of hibonite in order to relate the Ti oxidation state to the fO2 of the nebular system in which condensed. To that end, we report DFT calculations (0 K) to determine the ground-state energies and the enthalpy of formation (ΔH) of hibonite solid solutions that span the range reported in meteorites. Our results show that coupled substitution is energetically favored (ΔH=-96.70 kJ.mol-1, from oxides). In comparison, the formation of oxygen vacancies is energetically unfavorable, but similar to Ti3+ direct substitution for Al3+ (ΔH=∼60 kJ.mol-1, from oxides), which is commonly observed in hibonite. It is therefore necessary to consider oxygen vacancies as a potential mechanism for controlling the incorporation of Ti3+ into hibonite, in addition to direct replacement reactions. We provide here the first reliable estimation of the formation enthalpies for the hibonite solid solution that includes solutes and point defects. The results presented herein constitute a significant advance towards the establishment of a comprehensive Gibbs free energy description of the hibonite solid solution, which is ultimately required for accurate modelling of its thermodynamic stability within the early solar nebula.

CRYSTALS GROWTH OF AND CRYSTAL STRUCTURE OF SOLID SOLUTIONS IN THE Ag8SiS6 HOMOGENEITY REGION

Compounds with an argyrodite structure are a family of complex chalcogenides that demonstrate a wide range of properties: superionics, thermoelectrics, sensors, and photovoltaic materials. For sulfur-containing representatives, the main field of application is solid-state ionics. However, the formation of solid solutions is used to modify and improve the functional parameters of individual argyrodites. When solid solutions are formed by iso- or heterovalent substitution, an additional deformation of the crystal structure occurs, which increases the efficiency of ion transport. For the growth of single crystals, the method of direct crystallization by melt-solution technique was used. Based on the results of DTA, technological conditions for growing single crystals of solid solutions of Ag7.75P0.25Si0.75S6 and Ag7.5P0.5Si0.5S6 were developed. The temperature of the melt zone (Tmelt) was 50 K higher than the melting point of the solid solutions, and the temperature of the annealing zone (Tann) was 2/3 of their crystallization temperature determined by the DTA method. As a result, single crystals of dark gray color with a metallic luster were obtained. The crystal structure of the solid solutions of Ag7.75P0.25Si0.75S6 and Ag7.5P0.5Si0.5S6 was determined by the Rietveld method. Both solid solutions crystallize in a rhombic crystal system, SG Pna21, with lattice parameters: a = 15.06 Å, b = 7.44 Å, c = 10.54 Å (Ag7.75P0.25Si0.75S6) and a = 15.06 Å, b = 7.44 Å, c = 10.54 Å (Ag7.5P0.5Si0.5S6).

Utilization of Novel (KNbO3)1−x(Ba2FeNbO6)x (x = 0.1, 0.2, 0.3) Solid Solutions for Efficient Photo‐Assisted Fenton Degradation of Methylene Blue Dye

Novel (KNbO3)1−x(Ba2FeNbO6)x (x = 0.1, 0.2, 0.3) solid solutions corresponding to K0.82Ba0.18Fe0.09Nb0.91O3, K0.64Ba0.36Fe0.18Nb0.82O3, and K0.46Ba0.54Fe0.27Nb0.73O3 compounds have been synthesized via molten salt method. X‐ray diffraction confirms the formation of solid solutions, while transmission electron microscopy combined with energy‐dispersive spectroscopy results demonstrates a homogeneous distribution of elements. The obtained solid solutions crystallized in a cubic crystal structure, whereas the parent KNbO3 possesses an orthorhombic structure. The wide bandgap semiconductor KNbO3 transformed into a visible‐light‐active material, with its bandgap energy reduced from 3.56 eV to ≈2.4 eV. The substitution of K in KNbO3 with Ba is responsible for structural modification from orthorhombic to cubic symmetry, whereas both structural modification and the substitution of Nb with Fe correlated with optical properties. The photocatalytic activities of all obtained solid solutions are improved compared with the parent KNbO3 and Ba2FeNbO6 compounds for photocatalytic degradation of methylene blue (MB) dye. Among the series of solid solutions, K0.82Ba0.18Fe0.09Nb0.91O3 photocatalysts show the highest MB removal efficiency owing to its relatively higher surface area, suppressed charge carrier recombination, and more negative conduction band edge. Moreover, K0.82Ba0.18Fe0.09Nb0.91O3 photocatalyst (0.1 g) combined with hydrogen peroxide (H2O2) to form a novel photo‐Fenton system, achieving almost complete degradation of 100 mL of 10 mg L−1 MB dye in 30 min.

Improving fracture toughness and densification behavior of single‐phase TaC–HfC ceramic with carbon additives

AbstractThis investigation was undertaken to determine the role of carbon additives on the densification behavior and fracture toughness of TaC–HfC ceramic. The composition of TaC‐19 vol% HfC‐5 vol% VC with 10 vol% nano graphite/10 vol% nano carbon black was sintered by hot‐pressing (HP) method. Also, the sintering temperature varied from 1700°C to 2000°C. Vanadium carbide was used as a sintering aid to minimize the porosity for the given hot‐pressing temperatures while keeping the consolidation temperature low. The analysis of XRD patterns revealed that the sintering process led to the formation of a ternary solid solution in the samples accompanied by the entire consumption of HfC and VC phases. Also, the presence of carbon additives increased the relative density from 96% to 100% by enhancing the sintering temperature from 1700°C to 2000°C. It was significantly higher than the carbon‐free sample, which had a maximum value of 96.7% at 2000°C. The results also indicated that the maximum fracture toughness of 7.1 MPa.m1/2 was obtained for nano carbon black contained samples at the sintering temperature of 1900°C and above. The toughening mechanisms in samples were discussed, too.

Synthesis and Properties of CaMgSi2O6 - SrO Bioceramics for Enhanced Hydroxyapatite Formation and Cell Viability in Bone Regeneration

This study aims to synthesize and evaluate the properties of diopside (CaMgSi2O6) and strontium modified diopside (CaMgSi2O6-SrO) bioceramics for potential bone regeneration applications. The substitution of strontium for calcium leads to the formation of solid solutions: Sr-CaMgSi2O6, Ca-SrMgSi2O6, and a single phase of SrMgSi2O6, along with secondary phases of Ca-Sr2MgSi2O7 and Sr2MgSi2O7. This study is the first to examine the physical and biological properties of SrMgSi2O6 and its solid solutions. Microstructural analysis reveals that the pure diopside exhibits uniformly packed fine particles, while the SrO substitution results in lattice distortion and structural damage, thus weakening the mechanical properties and biodegradation resistance. The in vitro hydroxyapatite (HAp) formation ability of CaMgSi2O6-SrO bioceramics is comprehensively investigated, revealing that the re-adsorption of Mg2+/Sr2+ is a crucial factor. Pure diopside and Sr0.25 demonstrate effective HAp formation after immersion in simulated body fluid (SBF), with Sr0.25 showing finer particles and more uniform distribution due to appropriate Sr2+ re-adsorption. In contrast, SrO-rich samples show reduced HAp formation due to excessive re-adsorption of Mg2+ and Sr2+ ions, hindering HAp nuclei development. The cell viability test reveals that SrO substitution enhances cell viability due to increased surface area and the release of beneficial ions. Overall, Sr0.25 demonstrates excellent potential for bone regeneration applications by promoting HAp uniformity.

Leaching behavior of arsenic in coal under the action of mine water

Arsenic, a potentially harmful element in coal, has a detrimental effect on the quality of groundwater and the water cycle. There is a significant safety risk to the drinking water and overall health of residents living near mining areas. It is of great significance to explore the leaching pattern of arsenic in coal under the influence of mining and identify the main controlling factors for the prevention and control of groundwater pollution in mining areas. In this paper, we selected long flame coal and non-caking coal from Wulanmulun Mine, along with four types of water samples from the mine area, as the research subjects. Our aim was to investigate the leaching mechanism of arsenic in groundwater under the influence of coal-water interaction in the mine area. To achieve this, we conducted indoor batch coal-water leaching simulation experiments. The results show that: 1) The four leaching solutions, which correspond to four groundwater types at the coal mine production site, exhibit similar trends in the presence of arsenic ions after water-coal interaction. The leaching process can be divided into three distinct zones: a rapid descent zone, a dissolution shock zone, and a dissolution linear stable zone. The initial decline rate of arsenic content in different water samples is proportional to the initial concentration of arsenic in the water samples. 2) The dissolution of arsenic has a strong negative correlation with DO, and the lower the oxygen content in the solution, the higher the arsenic ion content. There is a relatively strong negative correlation with pH value. It has a strong positive correlation with the leaching of Mg, K, V, Cr, and Fe, and a relatively small positive correlation with the leaching of Mn and Cu. The leaching degree of Mg, K, V, Cr and Fe can be used as a sign to explore the leaching or content change of arsenic in actual mining environment. 3) Most arsenic in coal occurs in pyrite in the form of isomorphism or solid solution, and the dissolution of arsenic is related to pyrite content and its oxidative dissolution behavior. The higher the pyrite content, the greater its oxidation degree, and the higher the arsenic content in the solution. 4) Clay minerals, predominantly kaolinite, found in different coal samples demonstrate varying capacities for arsenic adsorption in the leaching solution. The results of this experiment indicate that the adsorption capacity of clay minerals in long flame coal is considerably higher than that observed in non-caking coal, leading to a substantial decrease in the concentration of arsenic ions in the solution. This reduction is associated with a notable decline in the arsenic concentration within the groundwater associated with the coal samples collected on-site. The results suggest that the leaching of arsenic from the coal samples will not lead to arsenic contamination in four distinct categories of groundwater. This finding holds considerable importance for the management and remediation of water pollution in mining contexts.

Microstructural Analysis of Stainless Steel Support/Ni-YSZ Anode Interface in Metal-Supported SOFCs

Solid oxide fuel cells (SOFCs) have attracted attention due to their high energy conversion efficiency and fuel flexibility. However, conventional anode-supported SOFCs composed solely of ceramics are susceptible to thermal stress such as rapid temperature rises and drops, which can cause cell cracks. Therefore, metal-supported SOFCs (MS-SOFCs) have been devised that use a stainless steel with excellent heat resistance as a support. In MS-SOFCs, elemental diffusion from the metal support during the cell manufacturing process causes microstructural changes in electrodes, leading to a reduction in cell performance [1, 2]. Although the microstructure and diffusion state of elements at the support layer/anode interface are different from those of conventional anode-supported cells, the phenomena as well as the chemical and physical states that occur at the interface have not been sufficiently studied. In this study, then, the microstructural characteristics of the stainless steel support/anode interface were quantitatively analyzed to understand the phenomena occurring and to develop methods to suppress the diffusion of metallic elements.Gd-doped CeO2 (GDC) was coated as a diffusion barrier layer (DBL) on a SUS430 stainless steel substrate by magnetron sputtering, followed by the NiO-YSZ (8 mol% Y2O3-ZrO2) slurry coating. The composition of SUS430 is given in Table 1. Samples without DBL were also fabricated. These samples were sintered at 1250 ºC for 10 hours in 50% H2-50% Ar. Three-dimensional reconstruction of the microstructures of these samples was performed using a focused ion beam-scanning electron microscope (FIB-SEM), and microstructural parameters were calculated. In addition, elemental diffusion at the interface was analyzed using an energy dispersive X-ray spectroscopy (EDS) analysis.When the sample was sintered at 1250 °C in a reducing atmosphere, the diffusion of Fe was significantly suppressed by the insertion of DBL. Therefore, it was confirmed that the GDC layer is effective to suppress the Fe diffusion as well as to prevent the formation of solid solution with Ni. However, no significant difference in Cr diffusion was observed. Furthermore, SEM observation revealed that the Ni surface was partially covered with Mn-Cr oxides. The formation of such a characteristic structure had a negative effect to reduce the effective triple phase boundary (TPB) length of the anode. Thus, it was concluded that the insertion of GDC layer suppressed the formation of Ni-Fe solid solution, while the patrial coverage of the Ni surface with Mn-Cr oxides reduced the effective TPB length.AcknowledgementsThis paper is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).[1] M.C. Tucker, J. Power Sources, 195, 15 (2010).[2] T. Franco, et al., ECS Transactions, 7, 771, (2007). Figure 1

Data-Driven Synthesis of Multi-Element Substituted Fluoride Crystals for Improved Ionic Conductivity

Barium fluoride (BaF2), with its fluorite-type structure, is anticipated to be a solid electrolyte material for high voltage fluoride-ion batteries. Previous studies have demonstrated that partial substitution of barium by lanthanum in BaF2 can increase the ionic conductivity by four to five orders of magnitude [1]. This finding implies that elemental substitutions could significantly improve the ionic conductivity of BaF2. However, a single elemental substitution limits the elemental exploration space, thereby reducing the chances of discovering compositions with high conductivity. Expanding the search space through multi-element substitution is expected to be effective; however, it is impractical to exhaustively explore over 3000 potential compositions in multi-elemental substitution. Therefore, we introduced a "Material-Conductivity Search Space" that offers a comprehensive overview of both the compositions of solid solutions and their conductivities, facilitating an efficient search. To create this system, we aimed to elucidate the relationship between the substitution elements and solid solution formation and conductivity properties using a data-driven approach. Based on the D-optimal design (D-opt), twenty candidate compositions for multi-element substitution were synthesized. Subsequently, additional experiments were performed using the data-driven design of experiment (DOE) approach. In this case, a regression model was constructed by using elemental species and amounts as the explanatory variables, and "number of peaks", which was extracted from the X-ray diffraction (XRD) pattern as the objective variable. Samples prepared using the data-driven DOE approach showed a significant reduction in the average 'Number of peaks' in XRD patterns, from 41.83 to 19.65, compared to those synthesized under D-opt guidance. This result indicates that data-driven approach can effectively search solid solution composition. Next, the electrical conductivity properties of the synthesized multi-elemental substituted BaF2 were examined at room temperature and revealed that their conductivities ranged from 10^-7 to 10^-3 S/cm. Notably, samples including potassium fluoride (KF) as a substitution element exhibited a significant enhancement in conductivity. We suggest that this improvement is due to the formation of additional ionic conduction pathways resulting from charge compensation, and/or activation energy change by multi-elemental substitution. We are now improving the material-conductivity search space by combining these experimental results as learning data. In the presentation, we will also report on the effective search for high conductivity materials using this system.Acknowledgments: This research was partially supported by the Aichi Knowledge Hub Aichi Priority Research Project and the Strategic Innovation Program (SIP) of the Cabinet Office.[1] Kazuhiro Mori, Atsushi Mineshige, Takashi Saito, et al., ACS Appl. Energy Mater., 2020, 3, 2873-2880.

Electrochemical Performance of Fuel-Electrode-Supported Reversible Solid Oxide Cells with a Ni-GDC Functional Layer

Introduction Reversible solid oxide cells (r-SOCs) can generate electricity in SOFC mode and produce hydrogen in SOEC mode. R-SOCs are promising electrochemical energy devices that can manage power derived from renewable energy sources by switching operating modes (1). Fuel-electrode-supported cells, which are widely used in both SOFCs and SOECs, exhibit higher performance even at lower operation temperature due to the use of thin electrolytes. Ni-yttria-stabilized zirconia (YSZ) is widely used as the fuel electrode material in fuel-electrode-supported cells because of its high ionic conductivity, high catalytic activity, and compatibility with electrolyte materials. However, Ni-zirconia based cermet such as Ni-YSZ tends to exhibit high polarization resistance, especially in the SOEC mode (2). Furthermore, degradation in the SOEC mode is also an issue (3), and further improvement of electrochemical performance and durability is necessary for the practical use of r-SOCs. Gadolinia-doped ceria (GDC) has higher ionic conductivity than YSZ, and, as a mixed ionic electronic conductor, the electrochemical reaction extends not only to the triple phase boundary (TPB) but also to the double phase boundary (DPB). Therefore, the electrochemical performance is expected to be improved by substituting Ni-YSZ with Ni-GDC. Here, in this study, a fuel-electrode-supported reversible solid oxide cell is prepared with a Ni-YSZ fuel electrode support and a thin Ni-GDC fuel electrode functional layer next to the electrolyte, and the electrochemical performance is evaluated. Experimental For experiments, a fuel-electrode-supported reversible solid oxide cell was used, as schematically described in Fig. 1. The cell consisted of a fuel electrode support, a fuel electrode functional layer, an electrolyte, a GDC buffer layer, and an air electrode. The materials of the fuel electrode support, the fuel electrode functional layer, and the electrolyte were Ni-(Y2O3)0.08(ZrO2)0.92 (YSZ), Ni-Gd0.1Ce0.9O2 (GDC), and YSZ, respectively, and the half-cell was fabricated by co-sintering these three layers. GDC has been reported to form a highly resistive solid solution with YSZ at high temperatures (4). Therefore, half-cells were fabricated at different co-sintering temperatures to investigate the influence of such solid solution on the cell performance. La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) was used for the air electrode, and the GDC buffer layer was inserted between the electrolyte and the air electrode to suppress interdiffusion. Current-voltage (I-V) characteristics were measured at 700–800 °C with a supply of 100 ml min-1 of 50%-humidified hydrogen (50 %H2O-50 %H2) to the fuel electrode, and 150 ml min-1 of air to the air electrode. Electrochemical impedance spectra were measured in the frequency range from 1 MHz to 0.1 Hz. Results and discussion Figure 2 (a) shows the I-V characteristics at 800 °C of the cells co-sintered at 1300 °C and 1350 °C. The cell co-sintered at 1300 °C exhibited higher I-V characteristics than the cell co-sintered at 1350 °C in both SOFC and SOEC modes. In the SOEC mode, the electrolysis current densities at the thermo-neutral potential (~1.29 V) of the cells co-sintered at 1350 °C and 1300 °C were 1.05 A cm-2 and 1.15 A cm-2 under these fabrication conditions, respectively. Both ohmic and polarization resistances were lower in the cells co-sintered at 1300 °C than in the cells co-sintered at 1350 °C, suggesting that lowering co-sintering temperatures than 1300 °C may further improve their I-V characteristics. The improvement in electrochemical performance by lowering the co-sintering temperature from 1350 °C to 1300 °C can be attributed to several factors, including an increase in TPB density due to a finer fuel electrode microstructure and a suppression of YSZ-GDC solid solution formation. A detailed analysis of these factors is needed in the future. In this presentation, the electrochemical performance of cells co-sintered at lower temperatures more than 1300 °C and the comparison of the performance of Ni-GDC functional layers with that of Ni-YSZ functional layers will also be presented and discussed. References Q. Minh, and M. B. Mogensen, Electrochem. Soc. Interface, 22, 55 (2013).Endo, T. Fukumoto, Y. Tachikawa, S. M. Lyth, J. Matsuda, and K. Sasaki, ECS Trans., 109 (11), 3 (2022).Moçoteguy, and A. Brisse, Int. J. Hydrogen Energy, 38, 15887 (2013).Tsoga, A. Naoumidis, and D. Stöver, Solid State Ionics, 135, 403 (2000). Figure 1

Chemically Stabilized Nasicon-Na1.5V0.5Nb1.5(PO4)3 Anode for Long-Life Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are considered as a potential solution for low cost and grid storage applications due to the more abundance of Na precursors compared to their Li analogues. For SIBs, several attractive candidates are available as cathodes such as layered oxides, Prussian blue analogues and polyanionic compounds but for the anodes hard is used as the primary choice for the fabrication of full SIBs.1-3 The NASICON (Natrium Super-Ionic CONductor) framework can be an efficient electrode material for SIBs due to its high structural and thermal stability along with superior sodium ion mobility. Recently, NASICON compounds are widely explored as cathode and solid-state electrolyte for SIBs and largely ignored as anodes due to their low capacity and high voltage. The general molecular formula for NASICON structure is NaxM2(PO4)3, where a maximum of four sodium can accommodate into the structure, which is built by lantern units, consisting of two MO6 and three PO4 corner shared with each other. We have studied the electrochemical (de)intercalation of sodium in empty NASION-Nb2(PO4)3 for the first time and showed its potential application in the anodes for SIBs.4 Nb2(PO4)3 is attracts lot of attention due to its high capacity (150 mAh g-1) and low voltage (1.4 V vs. Na+/Na0) which make it suitable candidate for SIBs anode. However, it suffers from rapid capacity decay due to the structural degradation, which is triggered by a lack of sufficient sodium ions at the Na (1) site (39% capacity retention after 200 cycles).To overcome this issue, we introduce extra sodium ions at Na(1) site via V3+ substitution gives the composition of Na1.5V0.5Nb1.5(PO4)3, which can act as the stabilizing agent to hold lantern units together during cycling.6 The Na-filled anode delivers reversible capacity of ~140 mAh g-1 at 1.2 V vs. Na+/Na0 through Nb5+/Nb4+/Nb3+ and V3+/V2+ redox activities, as predicted by density functional theory (DFT) calculations and confirmed by X-ray absorption spectroscopy (XAS). Additionally, the Na (de)intercalation mechanism changes from the multiple two-phase reactions (observed in the Nb2(PO4)3) to complete solid-solution formation in the sodium filled anode demonstrates the critical role of Na(1) site in the NASICON framework, in-line with DFT calculations, and enhances sodium diffusivity (≈ 10-9 cm2s-1), as deduced from in-situ X-ray diffraction (XRD) and galvanostatic intermittent titration technique (GITT) experiments. The anode retains 89% of its initial capacity retention at 5C after 500 cycles and extraordinary rate performances (105 mAh g-1 at 5C). When the NASICON-Na3V2(PO4)3 (NVP) cathode paired with the sodium filled anode, the full Na-ion cell delivers a remarkable energy density of 98 Wh kg-1 (based on the mass of anode and cathode) compared to the state-of-the-art NASICON-based Na-ion full cells and provides 80% capacity retention at 5C rate over 1000 long cycles. This work creates new opportunities for chemical and structural modifications that improve the electrochemical performance of NASICON anodes.

The thermodynamics of multicomponent high-entropy materials

AbstractHuman development has been based for millennia on manufacturing materials using a conventional alloying strategy of selecting a principal component for the primary property requirement of the material and then adding one or two minor alloying components at relatively low concentrations, either to enhance the primary property or to provide additional secondary properties. We have discovered relatively recently that, with sufficiently large numbers of alloying elements added in sufficiently large concentrations, the configurational entropy of mixing can often become large enough to suppress the formation of brittle compound phases, leading instead to the formation of multicomponent high-entropy solid solutions. In fact, there are literally billions of multicomponent high-entropy single-phase solid-solution materials, with a wide range of exciting new properties, in most cases relatively straightforward to manufacture by conventional processing methods. There seems, however, to be an upper limit to these effects, so that, beyond about ten or twelve alloying components, the inevitable increase in chemical diversity prevents the configurational entropy of mixing from suppressing the increasingly strong chemical reactions between them. This paper discusses in more detail the thermodynamic balance between: (1) increasing configurational entropy and promoting high-entropy solid solutions; and (2) increasing chemical diversity and promoting the formation of brittle compound phases. This is discussed on the basis of regular solution thermodynamics, without the need for more complex, semi-empirical Calphad calculations that can sometimes obscure the underlying key physical and chemical principles. The results show: (1) why large single-phase solid-solution regions are relatively common in multicomponent phase space; (2) why single-phase solid solutions are often favoured over stoichiometric compounds for large numbers of chemically similar components, in concentrated rather than dilute proportions, at high temperatures, and after quenching to room temperature; and (3) the difficulty of detailed thermodynamic analysis in multicomponent materials because of the large numbers of thermodynamic parameters that need to be known and the corresponding lack of underlying thermodynamic measurements.

Highly porous Ni/MgO-ZrO2 catalysts for dry reforming of methane and the effects of MgO addition on the mechanisms

Dry reforming of methane (DRM) is a promising pathway to convert greenhouse gas into syngas. However, the commonly used Ni based catalysts suffer deactivation due to severe sintering and coking. In this paper, a series of porous Ni/MgO-ZrO2 catalysts (5Ni/xM(1-x)Z, x = 0, 20, 40, 60, 80 wt%, respectively) with high specific surface area were synthesized by a facile combustion method followed by incipient impregnation. It is found that the appropriate amount of MgO (40 %) addition in ZrO2 favors high porosity and high specific area. More MgO enhances the basicity of the catalyst as well as the metal-support interaction (MSI) by the formation of NiO-MgO solid solution, thus improving DRM activity and coking resistance. However, excessive MgO addition leads to over-strong MSI and lower porosity, resulting in lower DRM activity. The catalyst with 40 % MgO addition (5Ni/40M60Z) exhibits the best activity (conversions of CH4 ∼ 76 %, CO2 ∼ 83 %) and stability (>50 h) at high GHSV = 96000 ml/gcat·h and 750 °C. in situ DRIFTS reveals the mechanism that MgO addition improves DRM activity and stability. Compared with ZrO2 where CO2 adsorbs as monodentate carbonate, CO2 tends to adsorb on 40 %MgO-60 %ZrO2 as bidentate carbonate and then easily transfer to more stable intermediate bidentate formate, thus improving DRM activity and coking resistance. This study provides new insights on the role of Mg addition in Ni/MgO-ZrO2 DRM catalysts.

Formation and Segregation of the Ru- and Rh-MgO Solid Solutions.

Structural changes in Ru- and Rh-loaded magnesium oxide (MgO) subjected to thermal treatment were investigated by using X-ray absorption spectroscopy. The thermal treatment of the MgO-loaded Ru and Rh nanoparticles led to the formation of Ru-MgO and Rh-MgO solid solutions, respectively. The valences of Ru and Rh in the solutions were 4+ and 3+, respectively, as determined by the Ru and Rh K-edge X-ray absorption near-edge structure (XANES). The degree of solid solution formation was the highest at 873 and 1073 K in Ru-MgO and Rh-MgO, respectively, as observed in the extended X-ray absorption fine structure and XANES analyses. The nearest neighboring Ru-O and Rh-O bond distances were shorter than the Mg-O bond in MgO. The dispersion of Ru and Rh on the MgO surface, measured by CO adsorption, increased for samples thermally heated at 1273 K, suggesting that the segregation of Ru or Rh from the solid solutions occurred at this temperature. Consequently, a relatively high dispersion was realized in the sample thermally heated to 1273 K. A good correlation was found between the dispersion value of Ru in Ru/MgO and the NH3 decomposition activity.

Investigation of the Influence of Bonding Parameters on the Homogenous Diffusion Bonding of Copper

Solid-state diffusion bonding (DB) of Copper-Copper (Cu/Cu) was carried out under varying bonding parameters (time and temperature) in argon shielding gas environment. Initially, the bonding was performed at bonding temperatures of 800, 850, and 900 °C for 60 minutes. Secondly, the bonding was carried out at holding times of 90, 120, and 150 minutes at 900 °C. The microstructural and mechanical properties of the bonding interface were evaluated via lap shear and micro hardness tests, X-ray diffraction, and Optical microscopy. It was found that the optimal bonding parameters for the joint interface was 950 °C for 150 minutes, resulting in maximum shear strength of 133 MPa. The X-ray diffraction also shows the formation of solid solution of Cu without the formation of any intermetallic compounds (IMC). The micro hardness test revealed a maximum hardness of 89 HV at the joint interface. Optical microscopy shows the formation of voids at the joint interface take place due to the Kirkendall effect, which increased with higher temperatures for longer time, and cause a wide diffusion-affected zone (DAZ).

Ti1-xAlxN or TiN + AlN: An investigation about Al influence on titanium aluminum nitride thin films structural organization

Ti1-xAlxN thin films with different Al contents (Ti0.8Al0.2N, Ti0.6Al0.4N and Ti0.4Al0.6N) were deposited by reactive magnetron sputtering in order to determine the real structure formed in these coatings: a single ternary nitride, with a substitutional solid solution formation, or the presence of two binary nitrides, TiN + AlN. The elementary composition, morphology homogeneity, chemical elements distribution, crystalline structure, grain size evaluation, modification on coatings structure and formed compounds were determined. GAXRD analyses evinced a grain size growth for all Ti1-xAlxN samples, suggesting that aluminum atoms are not present as a single AlN phase, but as a ternary nitride. In XPS analyses, N 1s spectrum for all samples exhibited a shift toward lower binding energies in Ti-N component, attesting the Ti-Al-N bond presence. Moreover, signatures of Al 3p and Ti 3d band shift were detected in the valence band region, confirming the Ti1-xAlxN solid solution formation for all deposited samples.

Enhancement of CO2 adsorption and oxygen transfer properties on γ-Al2O3 support through surface modification with MgO-ZrO2 for coke suppression over Ni catalyst in CO2 reforming of methane

This work focuses on employing commercial γ-Al2O3 for surface modification with MgO-ZrO2 mixed oxide to enhance the potential of CO2 adsorption and oxygen mobility. This enhancement facilitates its application as a support in catalysts for CO2 utilization such as CO2 reforming of methane (CRM). To achieve this perspective, γ-Al2O3 was modified with 10 wt.% of various MgO and ZrO2 contents (MgO:ZrO2= 10:0, 9:1,7:3, 5:5, 3:7, 1:9 and 0:10) using the impregnation method. All samples including unmodified γ-Al2O3 (Al) were characterized. Due to the increase in basicity and oxygen transfer around the surface, the improvement of the CO2 adsorption was observed on γ-Al2O3 modified with 9 wt.% MgO-1 wt.% ZrO2 (9Mg1ZrAl) and 10 wt.% MgO (10MgAl), respectively. An application of these two superior samples as a support of 10 wt.% Ni (10Ni) catalysts for CRM was investigated and compared with an unmodified γ-Al2O3. Characterization results suggest the formation of NiO-MgO solid solution at the surface due to the decrease in metal-support interaction and the increase in metal dispersion. The Ni catalysts with the surface-modified support show higher CO2 activity that raises carbon deposition resistance. The greatest coke prevention was observed on 10Ni/9Mg1ZrAl that lowers the coke deposition by 42 % compared to 10Ni/Al. It indicates that the composition of this modification allowed very low ZrO2 portion to merge with MgO and MgO to form solid solution with NiO. This enables the 10Ni/9Mg1ZrAl catalyst to generate labile oxygens which can be conveyed to the Ni metal sites on the catalyst.