Doping Elements Research Articles

Constructing oxygen vacancies by selective anion doping in high entropy perovskite oxide for water splitting

High entropy perovskite oxide (HEPO) is a potential electrocatalyst for the oxygen evolution reaction (OER), but insufficient activity remains a problem. Oxygen vacancies can activate the lattice oxygen to induce the lattice oxygen-mediated mechanism (LOM), which can avoid the kinetic limitation present in adsorbate evolution mechanism (AEM), thereby improving the OER activity. Herein, we select the appropriate doping element (S) through analysis of ionic radius, electronegativity, and oxygen vacancy formation energy, and report an effective two-step oxygen vacancy strategy for introducing oxygen vacancies into HEPO through electrospinning and sulfurization treatment. This strategy optimizes the eg orbital filling electron number and significantly increases the active area, oxygen vacancy content and electroconductivity. Furthermore, the apparent pH dependence and the TMA+ inhibition phenomenon suggest the involvement of the LOM. Consequently, the resulting S/LMO-E has a lower overpotential (314 mV at 10 mA cm−2) and faster kinetics, and shows excellent stability. Meanwhile, the water splitting is achieved at 1.59 V to afford 10 mA cm−2 current density for S/LMO-E⎪⎢Pt/C, which is smaller than that of RuO2⎪⎢Pt/C (1.62 V). This work provides an attractive OER electrocatalyst for efficient water splitting to produce renewable hydrogen and opens a new way for the design of effective and stable high entropy material electrocatalysts.

Engineering of g-C3N4 for Photocatalytic Hydrogen Production: A Review.

Graphitic carbon nitride (g-C3N4)-based photocatalysts have garnered significant interest as a promising photocatalyst for hydrogen generation under visible light, to address energy and environmental challenges owing to their favorable electronic structure, affordability, and stability. In spite of that, issues such as high charge carrier recombination rates and low quantum efficiency impede its broader application. To overcome these limitations, structural and morphological modification of the g-C3N4-based photocatalysts is a novel frontline to improve the photocatalytic performance. Therefore, we briefly summarize the current preparation methods of g-C3N4. Importantly, this review highlights recent advancements in crafting high-performance g-C3N4-based photocatalysts, focusing on strategies like elemental doping, nanostructure design, bandgap engineering, and heterostructure construction. Notably, sophisticated doping techniques have propelled hydrogen production rates to a 104-fold increase. Ingenious nanostructure designs have expanded the surface area by a factor of 26, concurrently extending the fluorescence lifetime of charge carriers by 50%. Moreover, the strategic assembly of heterojunctions has not only elevated charge carrier separation efficiency but also preserved formidable redox properties, culminating in a dramatic hundredfold surge in hydrogen generation performance. This work provides a reliable and brief overview of the controlled modification engineering of g-C3N4-based photocatalyst systems, paving the way for more efficient hydrogen production.

Investigation on the Thermal–Mechanical Properties of YbRESiO5 (RE = Yb, Eu, Gd, Ho, Tm, Lu, Y, Sc): First-Principles Calculations and Thermal Performance Experiments

Environmental barrier coatings are critically needed in the future to safeguard SiC-based ceramic matrix composites (SiC CMCs) used in gas turbines. Element doping of rare earth monosilicates could further improve the properties of the coating. The crystal structure, elastic properties, and resistance to water vapor corrosion of Yb2SiO5 and YbRESiO5 (where RE = Sc, Y, Eu, Gd, Ho, Tm, Lu) were examined in this study using first-principles calculations. When RE is Yb, the material is Yb2SiO5. Based on the outcomes of the calculation, we prepared YbRESiO5 (RE = Sc, Yb, Eu) and studied the thermodynamic properties. The findings show that YbReSiO5’s resistance to water vapor corrosion is as follows: YbLuSiO5 < YbEuSiO5 < YbGdSiO5 < YbYSiO5 < Yb2SiO5 < YbTmSiO5 < YbHoSiO5 < YbScSiO5. YbScSiO5 has a lower unit cell volume, average Re-O bond length, and thermal expansion coefficient than Yb2SiO5, while YbEuSiO5 has the reverse pattern. Moreover, of the eight materials, YbScSiO5 has the greatest elastic modulus and lattice distortion. After doping with Eu, YbEuSiO5 exhibits a decrease in thermal conductivity by nearly thirty percent compared to Yb2SiO5, due to the formation of oxygen vacancies. The development of environmental barrier coating materials may benefit from these discoveries.

Construction dual active sites on SnO2 via Fe doping for effective ciprofloxacin photodegradation

Adjusting the electronic structure via doping and enhancing the active sites of photocatalysts are proven strategies for improving the photodegradation of pollutants. However, the photodegradation mechanism involving doping elements and their impact on pollutant adsorption and activation at active sites remain unclear. In this study, Fe-doped SnO2 photocatalysts were synthesized using the hydrothermal method, featuring small particle sizes and highly active sites. It was found that doping SnO2 with 3 mol% Fe3+ significantly enhances its photocatalytic efficiency in degrading Ciprofloxacin, outperforming pure SnO2 by approximately 18.6 times. Spectroscopy methods, combined with density functional theory calculations, revealed that the presence of Lewis acid sites and oxygen vacancies serve as active sites in the Fe-doped SnO2 samples. Furthermore, a detailed photodegradation mechanism for Fe-doped SnO2 was proposed based on the band energy structure and analysis of free radical results. This research provides new insights into the mechanism of photocatalytic degradation of Ciprofloxacin by elucidating the interactions between the active sites of the photocatalyst and Ciprofloxacin molecules.

Study on interface characteristics of WC-Co doped Y rare earth element cemented carbide cutting tool and its influence on material properties

The influence of doping rare earth element Y on the material properties at the W and C interfaces of WC (0001)/Co (111) was studied using first principles calculations, taking into account adhesion work, interface energy, density of states, and Mulliken population. The grain size of WC-Co cemented carbide doped with rare earth element Y was analyzed before and after doping through cellular automata simulation. The microscopic morphology of the cemented carbide materials before and after doping with Y element was observed and analyzed by experiments, and their mechanical properties were tested. The research results have shown that the interface structure doped with Y has smaller interface energy, greater adhesion work, and stronger interface bonding ability. All four interface models exhibit metallic properties, and the addition of Y element enhancing the metallicity of WC-Co. The W-d and Y-p orbitals undergo orbital hybridization and generate covalent bonds, improving the durability and bonding strength of the material. The bond length of C-W at the interface after doping is smaller than that before doping, and the population is greater than that before doping, indicating an enhanced stability of the interface. After the addition of rare earth element Y, the crystals underwent through-crystal fracture, and the fracture showed irregular shapes, which improved the bonding strength of the interface. Through the cellular automata simulation, it was found that the grain size after doping with Y element was significantly smaller than that before doping, and it was experimentally verified that the doping of rare earth element Y played the role of grain refinement. At the same time, it could reduce the coefficient of friction of the material, and improve the overall performance of the cemented carbide material.

Enhanced secondary electron emission properties of sputter-deposited MgO–Au composite film via Cr doping

High and stable secondary electron emission yield (SEY) is essential for thin film materials used for electrical signal amplification in electronic devices. To enhance the secondary electron emission (SEE) capability of MgO–Au composite film, Cr-doped MgO–Au film was prepared by magnetron sputtering and the effect of Cr doping on the SEE properties of MgO–Au film was intensively investigated. It was confirmed that the doped Cr element is distributed through the whole composite film in a form of Cr2O3. Compared to the conventional MgO–Au film, the Cr-doped MgO–Au film with a Cr/(Cr + Mg) atomic ratio of 0.71 % achieves a SEY of 7.1 with a 4.4 % rise at the primary electron energy (Ep) of 300 eV and a maximum SEY of 10.9 with a 10.1 % increase at the Ep of 800 eV, and it also has a reduction of 49.2 % in SEE decay rate under continuous electron bombardment. For this novel composite film, the SEY ascension mainly attributes to the MgO grain enlargement and chemical stability enhancement, and the decreased SEE decay rate is associated with the improvements of resistance to electron bombardment and electric conductivity induced by Cr doping.

Accelerated Exploration of Li-Rich Cathode Materials with High Energy Density for Li-Ion Batteries

Li-rich cathode materials have been widely researched as promising cathode materials for Li-ion batteries due to the abundant numbers of Li+ in their formula units. There are, however, still some problems, such as the fading discharge voltage during cycling, to be overcome before its commercial application can be realized. In recent years, there has been a global expansion of efforts to innovate processes in material development by utilizing data science and materials informatics (hereafter referred to as MI), moving away from the traditional trial-and-error approach based on experiments. These initiatives have been surpassing the limitations of human-designed patterns and the number of feasible experiments, and examples of such endeavors are starting to be reported even in the field of battery materials[1]. In this study, we challenged a MI technology combined with first-principles calculation and database technology to widely search for suitable compositions of Li-rich cathode materials at high speed.Li1.4(Mn0.667Ni0.333)1-x Mx O2.35F0.05 (hereafter referred to as LMNOF, M: a dopant element, 0 ≤ x ≤ 0.01) was fabricated by a conventional method. The cathode was fabricated by mixing powder of the active material, acetylene black as a conducting powder and PTFE as a binder at the ratio of 7:2:1 by weight. The electrochemical performance was investigated using 2032 coin type half cells. The models for predicting battery performance were constructed by machine learning techniques. Composition formula information, synthesis conditions, and cell weight were used as candidate explanatory variables. XenonPy[2] was used for elemental-derived information. Principal component analysis was performed on the candidate explanatory variables, and only the variables determined to be important were used to construct the predictive model. The number of candidate M was narrowed down from approximately 100 to 30 based on the values of the enthalpy change between LMNOF with and without M. The enthalpy was calculated to determine the dopant elements for LMNOF by first-principles calculation. Specific M elements will be reported at the time of the presentation. The oxygen desorption energies of LMNOF with the 30 extracted elements were calculated to evaluate the stability of the LMNOF structure against the reaction in the fully charged state. Ten elements with negative values of the energy were selected as the dopant ones (Ms) for experimental demonstration of this study and the rest were used to predict the performance by using the database of the Materials Project[3]. The battery performance of M-doped LMNOF were predicted by the constructed model based on machine learning techniques with experimental data. This model indicated that the performances of LMNOF with a certain element M1 or M2 tended to be higher than ones with another M dopant elements at the stage where there had been no experimental data for M1 and M2. When the experiment was conducted for M1 and M2, the obtained data was turned out to be close to the predicted values and higher than ones with another M. These experimental demonstrations revealed that the constructed model at the initial stage in this study was suitable to predict the reasonable values for the composition without adequate experimental data. The loop of accumulating the experimental data and constructing the prediction model have been continuously carried out to improve the accuracy of predictions. As the number of experimental trials increased, the performance was gradually improved and the composition including M1 alone, M2 alone, M1 and other multiple Ms together, or M2 and other multiple Ms together, showed relatively higher performance, which, we considered, surpassed the maximum values obtained by the conventional trial-and-error experimental method. As a result, our new MI technology was demonstrated as an effective method to search for an unknown and unexplored composition with high performance due to the prediction accuracy of machine learning. In future, we are going to further improve prediction accuracy to find multiple Ms for even higher performance.

Sulfur-Phosphorus Doped Metal Composites As Superior Catalyst for Electrolytic Hydrogen Production in Real Seawater

In the face of the increasingly severe global energy crisis and challenges posed by climate change, promoting energy transition has become an international consensus. Among various renewable energy sources, hydrogen is considered an ideal energy carrier due to its clean and efficient characteristics. The electrolysis of seawater for hydrogen production has garnered widespread attention for its ability to fully utilize abundant seawater resources and the advantage of zero carbon dioxide emissions. However, achieving efficient, stable, and economically viable hydrogen production in seawater still faces many challenges, with catalyst design and optimization being recognized as key issues.Firstly, NiFe-LDH was synthesized using a simple one-pot solvothermal method. Subsequently, phosphorization, sulfurization, and sulfur-phosphorus co-doping were conducted to obtain samples namely NiFe-P, NiFe-S and NiFe-SP, respectively. Various electrochemical tests, including hydrogen evolution reaction (HER), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were firstly performed in simulated seawater to evaluate the electrochemical performance of the synthesized catalysts. The overall seawater splitting reaction was conducted with the same catalysts for both anode and cathode sides.After comparing the electrochemical activity of four different catalysts, it was found that NiFe-SP performs superior HER activity in alkaline simulated seawater. NiFe-SP required merely -0.143 V to deliver 100 mA cm-2 current density, which was 95 mV lower than NiFe-LDH to achieve the same current density. In EIS tests, NiFe-SP exhibited a smaller charge transfer resistance than NiFe-LDH, and NiFe-SP had the largest double-layer capacitance (Cdl) value in ECSA measurements, indicating that NiFe-SP possessed and lowest reaction resistance and the maximum electrochemically active surface area.X-ray Diffraction (XRD) and Raman spectroscopy analyses indicate that the catalyst, after sulfur-phosphorus doping, does not exhibit a pure-phase LDH structure but transforms into a heterogeneous structure of Ni3S2 and FeS2. Scanning Electron Microscopy (SEM) observations suggest that sulfur-phosphorus co-doping causes the original spherical structure of NiFe-LDH to aggregate, with the appearance of some lamellar structures on the surface. Energy Dispersive Spectroscopy (EDS) also confirms the successful doping of sulfur and phosphorus elements into NiFe-LDH, with uniform distribution on the material's surface.Finally, the catalyst underwent a 2000-hours continuous stability test at a constant current of 100 mA cm-² in real seawater. The results indicate that the potential of NiFe-SP increased by only 5%, demonstrating that the doping of sulfur and phosphorus not only reduces the catalytic overpotential but also significantly sustains potential retention. This suggests that the metal composite structure obtained after sulfur-phosphorus co-doping is well-formed and stable. The systematic electrochemical tests and stability evaluation in this study highlights the potential of sulfur-phosphorus co-doped metal composite NiFe-SP as an efficient and stable catalyst for real seawater electrolysis. This not only contributes to a deeper understanding of the fundamental principles governing catalyst behavior but also opens new possibilities for the practical application of hydrogen production technology. Figure 1

Origin of Stability and Activity Enhancements in Pt-Based Oxygen Reduction Reaction Catalysts Via Defect-Mediated Dopant Adsorption

Platinum alloys are highly efficient electrocatalysts for the oxygen reduction reaction (ORR) in acidic conditions. However, these alloys are susceptible to metal loss through leaching and degradation, leading to reduced catalyst stability and activity. Recently, it has been shown that doping with oxophilic elements can significantly alleviate these problems, with a prominent example being Mo-doped Pt alloys. Here, to achieve atomic scale understanding of the exceptional activity and stability of these alloys, we present a detailed density functional theory description of the dopants’ structures and impact on electrocatalyst properties. Beginning with the Mo/Pt system, we demonstrate that Mo can be stabilized in the form of low-dimensional oxyhydroxide moieties on Pt defects. The resulting structures enhance stability and activity via distinct physical processes, with the Mo moieties both directly inhibiting Pt dissolution at defects and indirectly enhancing ORR activity by generation of strain fields on surrounding Pt terraces. We then generalize these analyses to other metal dopant elements, and we demonstrate that similar low-dimensional oxyhydroxide structures control the electrocatalytic properties through an intricate interplay of the structures’ acid stability, intrinsic activity for the ORR, and ability to induce ORR-promoting strain fields on Pt.Reference:Sawant, K., Zeng, Z. & Greeley, J., Angew. Chem., Int. Ed., 10.1002/anie.202312747

Schottky-Barrier-Free Plasmonic Photocatalysts for Solar-Driven Ammonia Synthesis

Ammonia is not only an indispensable feedstock to produce essential industrial chemicals like fertilizers, but it is also a potential hydrogen energy carrier owing to its high energy density and hydrogen capacity. Currently, most ammonia required for humans comes from the Haber–Bosch process, which contributes more than 90% of the annual global ammonia output. However, the harsh reaction conditions of this process result in serious energy and environmental issues. According to the relevant statistics, the ammonia industry consumes about 2% of the total energy and generates about 1.6% of the total CO2 emission annually in the world.It is therefore crucial to develop a green and sustainable strategy for ammonia synthesis. Among various alternative technologies of the Haber–Bosch process, artificial photosynthesis has attracted wide research interests and has been regarded as a promising, environmentally friendly, and energy-saving process. Photocatalytic ammonia synthesis can utilize renewable solar energy to drive the reaction and operate under mild conditions, which possesses the benefits of the simple reaction system, low cost, and safety. Although numerous photocatalysts have been explored over the past several decades, their activity and efficiency have still been low and far from the practical application requirements. It is therefore a huge challenge to design efficient photocatalysts for ammonia synthesis.Localized surface plasmon resonance (LSPR) has recently drawn enormous attention. LSPR can not only endow plasmonic nanomaterials with large absorption cross-sections and intense local field enhancement but also generate energetic hot electrons and hot holes. Owing to the appealing features of LSPR, plasmonic photocatalysis has shown great potential in ammonia synthesis. Plasmonic photocatalysts are usually composed of noble metals and wide bandgap semiconductors. However, the Schottky barrier will form at the metal–semiconductor interface in such hybrid structures due to the mismatch of the band structures between plasmonic metals and semiconductors. Hence, a large portion of the hot electrons cannot cross the Schottky barrier and get lost in the metal through the recombination with the holes. To overcome the drawbacks caused by the Schottky barrier, it is strongly desirable to develop a new type of plasmonic semiconductor photocatalysts, i.e., Schottky-barrier-free plasmonic photocatalyst.The Schottky-barrier-free plasmonic photocatalysts are usually degenerately doped semiconductors containing lattice oxygen vacancies. They possess high free electron densities and strong plasmon resonance because of the high-level doping, which results in abundant hot charge carriers upon plasmon excitation. Moreover, they also have appropriate surface sites that can adsorb reactant molecules and activate them. The photogenerated plasmonic hot charge carriers can get trapped at the defect sites and thereafter drive redox reactions. Compared with traditional metal–semiconductor hybrid plasmonic photocatalysts, Schottky-barrier-free plasmonic photocatalysts enable hot charge carriers to be transported nearly freely in the material, resulting in high charge utilization and photocatalytic efficiency.We have demonstrated the synthesis of Schottky-barrier-free plasmonic MoO3−x nanospheres (NSs) with remarkably high oxygen vacancy (OV) contents by aerosol-spray. The MoO3−x NSs can achieve efficient ammonia photosynthesis through a “killing two birds with one stone” mechanism. On the one hand, the OVs can serve as chemisorption sites for N2 molecules and participate in their activation. On the other hand, the introduction of OVs generates a large number of free electrons near the conduction band, which induces a broad absorption band from the visible to the NIR region owing to the plasmon resonance. The Schottky-barrier-free nature of this plasmonic semiconductor allows free transportation of the plasmonic hot charge carriers, while the defect states introduced by the OVs can effectively trap the hot electrons to prevent rapid electron–hole recombination. As expected, the as-prepared material exhibits a superior ammonia production rate, with the highest apparent quantum efficiency (AQE) of 1.24% at 808 nm and an appreciable solar-to-ammonia conversion efficiency (SACE) of 0.057% for NH3 production. Besides MoO3−x , WO3−x is also an excellent candidate for Schottky-barrier-free plasmonic photocatalysts. We have synthesized square WO3−x nanoplates hydrothermally. The WO3-x nanoplates possess regular morphology, wide light absorption, and great ammonia production performance. Furthermore, by introducing doping elements (Mo, V, Fe, Bi) into WO3−x nanoplates, the N2 activation and dissociation can be improved by refining the defect states. The Mo-doped WO3−x nanoplates exhibit the highest ammonia production rate of 145.50 μmol g−1 h−1 with SACE of 0.011% since the Mo species can promote the chemisorption and polarization of N2 molecules and significantly reduce the reaction barrier. Notably, Mo-doped WO3−x nanoplates are a dual-function photocatalyst that can oxidize water to hydrogen peroxide in a stoichiometric ratio while synthesizing ammonia. Figure 1

Chalcogen Doping in SnO2: A DFT Investigation of Optical and Electronic Properties for Enhanced Photocatalytic Applications.

Tin dioxide (SnO2) is an important transparent conductive oxide (TCO), highly desirable for its use in various technologies due to its earth abundance and non-toxicity. It is studied for applications such as photocatalysis, energy harvesting, energy storage, LEDs, and photovoltaics as an electron transport layer. Elemental doping has been an established method to tune its band gap, increase conductivity, passivate defects, etc. In this study, we apply density functional theory (DFT) calculations to examine the electronic and optical properties of SnO2 when doped with members of the oxygen family, namely S, Se, and Te. By calculating defect formation energies, we find that S doping is energetically favourable in the oxygen substitutional position, whereas Se and Te prefer the Sn substitutional site. We show that S and Se substitutional doping leads to near gap states and can be an effective way to reduce the band gap, which results in an increased absorbance in the optical part of the spectrum, leading to improved photocatalytic activity, whereas Te doping results in several mid-gap states.

Constructing Metal-Organic Framework Films with Adjustable Electronic Properties on Hematite Photoanode for Boosting Photogenerated Carrier Transport.

Hematite (α-Fe2O3) has become a research hotspot in the field of photoelectrochemical water splitting (PEC-WS), but the low photogenerated carrier separation efficiency limits further application. The electronic structure regulation, such as element doping and organic functional groups with different electrical properties, is applied to alleviate the problems of poor electrical conductivity, interface defects, and band mismatch. Herein, α-Fe2O3 photoanodes are modified to regulate their electric structures and improve photogenerated carrier transport by the bimetallic metal-organic frameworks (MOFs), which are constructed with Fe/Ni and terephthalate (BDC) with 2-substitution of different organic functional groups (─H, ─Br, ─NO2 and ─NH2). The α-Fe2O3 photoanode loaded with FeNi-NH2BDC MOF catalyst exhibits the optimal photocurrent density (2mAcm-2) at 1.23VRHE, which is 2.33 times that of the pure α-Fe2O3 photoanode. The detailed PEC analyses demonstrate that the bimetallic synergistic effect between Fe and Ni can improve the conductivity and inhibit the photogenerated carrier recombination of α-Fe2O3 photoanodes. The ─NH2 group as an electron-donor group can effectively regulate the electron distribution and band structure of α-Fe2O3 photoanodes to prolong the lifetime of photogenerated holes, which facilitates photogenerated carrier transport and further enhances the PEC-WS performance of α-Fe2O3 photoanode.

Enhanced thermoelectric properties of n-type sulfide compound Bi2SeS2 by Cl doping

Sulfides composed of an eco-friendly and low-cost composition have received widespread attention as a substitute for traditional thermoelectric materials. However, n-type sulfides with high performance are rare compared with p-type ones. This work revealed that Bi2SeS2 with n-type conductivity characteristics is a potential thermoelectric material, whose ZT value reaches ∼ 0.70 at 773 K for the Cl doped sample Bi2Se0.98S2Cl0.02. Cl serving as a carrier donor can increase the electrical conductivity by optimizing the carrier concentration. Coupled with a moderate Seebeck coefficient in the range of 100–200 μV/K, a high power factor of ∼6.46 μWcm−1K−2 at 773 K was achieved. In addition, the lattice thermal conductivity reduces because of the formation of precipitates, as well as the induced mass and stress fluctuations due to the doping of heterogeneous Cl element, which effectively suppress the increase in total thermal conductivity. The combination of optimized power factor and low thermal conductivity leads to a final high ZT value, which is relatively higher than or comparable to most other reported n-type sulfide thermoelectric material.

Partially recrystallized heterostructure via Mo-doping endows CoCrNi medium-entropy alloy with exceptional strength and ductility

CoCrNi medium-entropy alloy (MEA) has excellent ductility, but the low strength at room temperature limits its practical usage. This study proposes an effective strategy to enhance the strength of CoCrNi MEA without apparent loss of ductility via partially recrystallized heterostructures resulted from doping of large atomic radius element, which was substantiated in a Mo-doping (CoCrNi)98Mo2 MEA. Compared with CoCrNi, the strength of (CoCrNi)98Mo2 is remarkably improved, maintaining the high uniform elongation of ∼24%. The yield strength and ultimate tensile strength increased from 950 MPa, 1287 MPa to 1131 MPa, 1564 MPa, respectively. The difference in deformation between the soft recrystallized region (SRR) and the hard non-recrystallized region (HNRR) leads to an excellent hetero-deformation induced (HDI) strengthening. Additionally, it is easier to reach the critical stress of twinning caused by high HDI stress at the interface of SRR/HNRR, which contributes to activation of high-density twins and produce dynamic Hall-Petch strengthening effect.

Copper Vanadium Oxide Yolk-Shell Microspheres with Excellent Capacitance and Cycling Performance for Electrochromic Supercapacitor.

Vanadium pentoxide (V2O5) is considered a promising material for electrochromic supercapacitors due to its rich color transitions and excellent electrochemical capacity. However, V2O5 exhibits low electrical conductivity, and its volume changes dramatically during charge-discharge cycles, leading to structural collapse and poor long-term cyclability. These issues have hindered the development and application of V2O5. In this study, copper vanadium oxide yolk-shell microspheres (CVO) were synthesized through a one-step solvent heat treatment with an annealing process. With the doping of copper element, the capacitance, conductivity, and cyclic stability of CVO microspheres were significantly enhanced. Subsequently, the sphere-wire network structure was formed by blending Na2V6O16·3H2O nanowires (NVO), resulting in the formation of CVO/NVO composites. The three-dimensional sphere-wire network efficiently facilitates the acquisition of additional redox sites and strengthens the material-to-substrate bonding. Under the combined influence of these favorable factors, CVO/NVO achieved a high specific capacitance of 39.2 mF cm-2, with a capacitance retention of 84% after 7500 cycles at a current density of 0.7 mA cm-2. The fully inorganic solid-state electrochromic supercapacitor (ECSC), assembled on the basis of CVO/NVO, demonstrates a vivid and clearly distinguishable color change (ΔE* = 37). Even more impressive is the energy storage capacity (18.4 mF·cm-2) and the cycling stability (up to 89% retention after 10,000 cycles) exhibited by the devices. These key performances are superior to those of most of the previously reported V2O5-based ECSCs, opening a promising avenue for the development of V2O5-based electrochromic energy storage devices.

Thermoelectric properties enhancement and optimization of SnTe-based material with single doping: RSM-ANN approach

Tin Telluride (SnTe) stands out among semiconductor materials, drawing attention as an environmentally friendly alternative to conventional Lead Telluride (PbTe). This study explores the novel incorporation of titanium (Ti) and zirconium (Zr) as dopant elements in SnTe-based materials, an approach that has never been previously investigated. Leveraging mathematical modeling and machine learning methodologies, we use Response Surface Methodology (RSM) and Artificial Neural Network-Genetic Algorithm (ANN-GA) to predict thermoelectric properties of SnTe-based materials and find the optimum dopant element addition and operating temperature. Eleven samples featuring varying Ti and Zr concentrations are employed in experimental investigations, with dopant amounts ranging from 0 to 0.05 M. Characterization of each sample is conducted across a temperature spectrum from 50 to 450 °C, yielding a comprehensive dataset of 99 entries for neural network model construction. The generated RSM and ANN models demonstrate remarkable predictive accuracy for the thermoelectric properties of SnTe-based materials, showcasing coefficient of determination (R2) values spanning from 0.986 to 0.998. This study uses RSM and ANN-GA to predict an optimized zT value of 0.558. This value surpasses the highest zT value from the experiment by 3.33 %. In conclusion, this investigation underscores the potency of RSM and ANN as valuable tools for advancing research on SnTe-based thermoelectric materials, exemplifying their capacity to hasten the exhausting process of finding the optimum dopant addition and operating temperature.

Structural evolution mechanism and magnetic properties of soft magnetic composites transformed from FeSiAl/Co3O4 composites

Simultaneous optimization of core loss and saturation magnetization in soft magnetic composites (SMCs) is crucial for the development of high frequency and high power in power electronic devices. In this work, FeSiAl/(Al2O3-Co) and FeSiAlCo/Al2O3 SMCs were prepared by sintering FeSiAl/Co3O4 composite powders at different temperatures. The corresponding structural evolution mechanism and magnetic properties of the prepared SMCs were studied systematically. When the sintering temperature was below 950 ℃, a chemical reaction at the FeSiAl/Co3O4 interface occurred and led to the formation of Al2O3-Co composite coating. The Al2O3 coating, as an isolation band, can effectively hinder the interdiffusion between Co coating and FeSiAl magnetic powder. When the sintering temperature increased to above 1000 ℃, the interdiffusion began to occur and was accelerated by the high temperature and chemical potential educed by concentration gradient, finally resulting in the formation of FeSiAlCo alloy. The prepares SMCs exhibited a low core loss due to the high integrity of Al2O3 coating. Its saturation magnetization and permeability significantly increased with the sintering temperature due to the generation of Co coating with ferromagnetism. This work provides a new strategy for the construction of ceramic oxide coating with high integrity and elemental doping of magnetic powder in SMCs, which is expected to be applied to the preparation of high-performance SMCs.

Study on Ca-doping effects and structural stability in Bi2Sr2-xCaxCuO6+δ (0 ≤ x ≤ 1.2) compounds by Rietveld refinement and high-pressure Raman spectroscopy

The lattice distortion induced by element doping is regarded as an effective approach to improve the superconductivity of Bi-based superconductors. In this study, a series of Bi2Sr2-xCaxCuO6+δ (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 and 1.2) ceramic samples are prepared by Pechini sol-gel method. The Ca-doping effects, structural stability and superconductivity of Bi-2201 phase are studied by electron microscopy, high-pressure Raman spectroscopy, the standard four-probe technique, X-ray diffraction and Rietveld refinements. Results indicate that all samples are constituted by Bi-2201 main phase and Ca8.56Sr5.44Bi16O38 impurity. It can be determined that Ca atoms have entered Bi-2201 orthorhombic lattice and preferentially occupied the Sr-sites. When Ca atoms are introduced and high-pressure is exerted, the Bi-2201 lattice can present a relatively high structural stability. Meanwhile, the correlations between doping amount x, Cu–O–Cu bond angle (θ), carrier concentration of CuO2 planes and superconducting onset transition temperature (Tc,onset) are discussed particularly. It should be noted that the Bi-2201 lattice has the largest θ, the highest carrier concentration and the highest Tc,onset value of 84.98 K when x = 0.8.

Phase structure evolution and its effect on magnetic and mechanical properties of B-doped Sm2Co17-type magnets with high Fe content

Abstract The unique cellular microstructure of Fe-rich Sm2Co17-type permanent magnets is closely associated with the structure of the solid solution precursor. We investigate the phase structure, magnetic properties, and mechanical behavior of B-doped Sm2Co17-type magnets with high Fe content. The doped B atoms can diffuse into the interstitial vacancy, resulting in lattice expansion and promote the homogenization of the phase organizational structure during the solid solution treatment in theory. However, the resulting second phase plays a dominant role to result in more microtwin structures and highly ordered 2 : 17R phases in the solid solution stage, which inhibits the ordering transformation of 1 : 7H phase during aging and affects the generation of the cellular structure, and to result in a decrease in magnetic properties, yet the interface formed between it and the matrix phase hinders the movement of dislocations and enhances the mechanical properties. Hence, the precipitation of high flexural strain grain boundary phase induced by B element doping is also a new and effective way to improve the flexural strain of Sm2Co17-type magnets. Our study provides a new understanding of the phase structure evolution and its effect on the magnetic and mechanical properties of Sm2Co17-type magnets with high Fe content.

DFT study on doping effect of different transition metals on MoS2 for enhancing the formation of S vacancies

MoS2 modification by doping transition metals is an effective way to change the Mo–S bond energy by taking advantage of the electronic variability of the d orbitals of transition metals. Herein, this study investigates the doping effect of different transition metals onto MoS2 edge sites through DFT calculations. To screen out the metal additive effect, different transition metals were doped to the MoS2 edge sites to see the effect on generating S vacancies that were generally regarded as the active sites. DFT simulation results proved that the ability of the valence electrons to populate the orbitals with the greatest overlap with the orientation of the edge Mo–S bond was a major factor in how simple it was to create S vacancies at the Mo-edge and S-edge sites. For the transition metals, the vacancy formation energy increases with the increase of periodic number for the same group, while decreases with the increase of the atomic weight for the same period. This implied that the upper right corner transition metals in the Periodic Table could be selected to modify MoS2 to obtain the minimum vacancy formation energy. Therefore, nickel and cobalt are the best choice as the doping element for modifying MoS2.