Ferroelectric ceramics generate a strain property in electric field due to the inverse piezoelectric effect and ferroelectric domain swiching, and these ceramics can be made as key components of actuators. Lead-based ferroelectric ceramics are widely used in actuators, but their high lead level is harmful to human-being health and environment. (K_1-xNa_x)NbO₃-based ceramics replace lead-based ceramics for actuators applications. (K_1-xNa_x)NbO₃-based ceramics with a multi-phase coexistence structure at room temperature have a high strain due to the possible increasing polarization direction. The classical (1-x)(K_1-yNa_y)(Nb_1-zSb_z)O₃-xBi_0.5(Na_1-wK_w)_0.5ZrO₃ (0≤x≤0.05, 0.40≤y≤0.68, 0≤z≤0.08, 0≤w≤1) (KNNS-BNKZ) system can be adjusted to have rhombohedral-tetragonal (R-T), rhombohedral-orthogonal-tetragonal (R-O-T), orthogonal-tetragonal (O-T) phases coexisted structures to increase the strain property. When the system is used to construct the coexistence structure, the composition and process need to be finely regulated, especially the raw material calcination or pre-firing process. Pre-firing is a solid-phase reaction of various raw materials at a certain temperature, and the purpose is to synthesize the crystal structure of the target component without raw material components. The activity, particle size and uniformity of the pre-fired powder have a great influence on the difficulty of green sintering and the electrical properties of ceramics. The pre-firing temperature affects the phase coexist structures of 0.96(K_0.5Na_0.5)(Nb_0.96Sb_0.04)O₃-0.04Bi_0.5(Na_0.5K_0.5)_0.5ZrO₃ ceramic coming from KNNS-BNKZ system, but the effect of the strain properties of ceramics is not reported yet. In this paper, 0.97(K_0.48Na_0.52)(Nb_0.97Sb_0.03)O₃-0.03Bi_0.5(K_0.48Na_0.52)_0.5ZrO₃ (0.97KNNS-0.03BNKZ) with R-T was designed according to KNNS-BNKZ system. KNN-based ceramics with multi-phase coexistence for improving their strain properties were constructed via adjusting the pre-firing temperature. In addition, the effect of pre-firing temperature on the phase structure, dielectric properties, ferroelectric properties and strain properties of 0.97KNNS-0.03BNKZ ferroelectric ceramics was investigated.

For the preparation of 0.97KNNS-0.03BNKZ ferroelectric ceramics by a solid-phase sintering method, the ingredients were made according to the chemical formula, and various raw materials were mixed and ground with absolute ethanol in a ball mill with zirconia balls. After 12_h milling, the slurry was dried. The mixture of 0.97KNNS-0.03BNKZ components of 20.0 g in a crucible was calcined at 600-950 ℃ for 3 h. After milling and drying, the powder was pressed into green discs with the diameter of 13 mm. The upper and lower surfaces of the green discs were buried with the same calcination powder, covered with alumina crucible then sealed with alumina powder. Finally, the green discs were sintered in a high-temperature furnace at 1 180 ℃ for 3 h. The ceramic samples were obtained after cooling in the furnace.

The samples were not polished and thermally corroded. The surface morphology of the ceramics was determined by a model Smartlab 3 kW scanning electron microscope after direct cleaning and drying. The density of the samples was analyzed by the Archimedes drainage method. After grinding the surface of samples, the phase structure of the ceramics was characterized by X-ray diffracometer (XRD). Their ferroelectric and strain properties were determined at 10 Hz by a model Precision Premier II ferroelectric system. Their permittivity was measured at 10 kHz by a model TZDM permittivity instrument.

The effect of calcination temperature (i.e., 600-950 ℃) on the diameter shrinkage, density, relative density, microstructure, crystal structure, dielectric properties, ferroelectric properties and strain properties of 0.97KNNS-0.03BNKZ ceramics was analyzed. The results show that the diameter shrinkage density and relative density of these ceramics firstly increase and then decrease with the increase of the calcination temperature. The ceramics calcinated at 800 ℃ have the maximum relative density (i.e., 94.9%), while the ceramics calcinated at 600 ℃ and 950 ℃ have the minimum relative density (i.e., 80.3% and 80.4%). All of the ceramics have the same distorted orthogonal crystal structure based on the XRD patterns and temperature-dependence of dielectric constant. Their Curie temperature increases from 280 ℃ to 320 ℃, while their dielectric constant increases from 4 520 to 7 769. The maximum polarization strength (P_max) of the ceramics at 600, 800 ℃ and 950 ℃ is obtained due to the easy domain swiching for the high or small relative density of ceramics. At 950 ℃, the bipolar strain of the ceramics reaches 0.5% at 60 kV/cm because the ferroelectric domain is easy to swiching, and the interacts between defect dipoles and domain swiching. At 600-900 ℃, the strain properties of the ceramics change slightly (i.e., 0.2%-0.3% strain). The unipolar strain properties of ceramics calcinated at different temperatures are similar.

The pre-firing had little effect on the crystal structure of 0.97KNNS-0.03BNKZ ceramics, but had a great effect on the density and strain performance of the ceramics. When the calcination temperature was 950 ℃, the bipolar strain of the ceramics reached 0.5% at 60 kV/cm, because the ferroelectric domain was easy to swiching and the interacts between defect dipoles and domain swiching.

The development of PEM water electrolysis for hydrogen production is currently flourishing, yet achieving a large-scale commercialization still requires overcoming several technical challenges. The extensive research on Ir- and Ru-based materials notably advances the development of highly active and stable OER catalysts, playing a crucial role in designing commercially viable PEM water electrolysis technology. Despite significant advancements in the research of such OER catalysts, there are still some issues that need to be addressed. The challenge of Ir-based catalysts remains in reducing the Ir content in catalysts and the Ir loading in membrane electrodes, while ensuring high activity and stability. Developing low-cost metal-supported catalysts with high stability and conductivity is an effective approach to reduce Ir usage. Metal oxides of specific elements (i.e., Ti, Ta, Nb, W, and Mo) can stably exist under strong acidic and oxidizing conditions, demonstrating a good corrosion resistance, which is the potential candidates for substrates. Furthermore, enhancing the continuity of Ir-based catalysts and forming a dense conductive layer can improve the conductivity of these metal oxide supports. Enhancing the stability of Ru-based catalysts is a challenge to commercial application. Reducing the proportion of unstable Ru elements through supported or solid solution-type Ru-based catalysts can stabilize catalysts under acidic OER conditions. Suppressing the lattice oxygen participation in OER can prevent the structural collapse of Ru-based catalysts, and the mechanisms of Ru self-deposition phenomenon are required a further exploration. Finally, it is important to establish a unified and comprehensive testing standard system for assessing the activity of catalysts in the PEM water electrolysis, particularly under high current density conditions.

Micron-sized SiO₂ hollow microspheres were prepared by a hard template encapsulation method and an ethyl acetate etching process with polystyrene (PS) as a template, hexadecyltrimethylammonium bromide (CTAB) as a surface modifier, and tetraethyl orthosilicate (TEOS) as a silicon source, and vertically deposited self-assembled into micron-sized SiO₂ hollow microsphere photonic crystals. The effects of TEOS content and etching conditions on the morphology of hollow microspheres, as well as the effect of vertical deposition self-assembly solution concentration on the infrared properties of micrometer sized SiO₂ hollow microsphere photonic crystals were investigated.

For the preparation of micron-sized PS@SiO₂ microspheres, 0.15 g of polystyrene microspheres with the size of 1.5 μm were dissolved in 160 mL of deionized water and 80 mL of anhydrous ethanol. After ultrasonic dispersion, 0.03 g of CTAB was added to modify the surface of the polystyrene template under stirring. After 30 min, 3 mL of 25% ammonia water was added to prepare solution A. 0.2 mL of ethyl orthosilicate was dissolved in 5 mL of anhydrous ethanol to prepare solution B. Solution B was mixed with solution A under stirring at room temperature for 24 h. The reacted solution was filtered and washed with anhydrous ethanol and deionized water for three times. PS@SiO₂ material was obtained after drying.

For the preparation of micron-sized SiO₂ hollow microspheres, 0.5 g of PS@SiO₂ microspheres were dispersed in 20 mL of ethyl acetate, and heated at 60 ℃ for 10 min after ultrasonic dispersion. The PS template was etched off by ethyl acetate. Subsequently, the slurry was filtered and washeda with anhydrous ethanol and deionized water for three times to obtain micron-sized SiO₂ hollow microspheres.

For the preparation of micron-sized SiO₂ hollow microsphere photonic crystals, a microsphere suspension was dispersed for a certain time, and then a cleaned hydrophilic glass substrate was vertically immersed into the microsphere suspension, and dried at 60 ℃. As the mixed solvent evaporates, the microspheres self-assemble on the surface of the substrate into a photonic crystal thin film with an opal structure.

Micron-sized SiO₂ hollow microspheres with a low damage rate, a good dispersibility, and a high sphericity were prepared with PS spheres as a template, CTAB as a surfactant, and TEOS as silicon source. PS template was removed via ethyl acetate etching. At TEOS content of 0.2 mL, PS@SiO₂ microspheres are tightly coated, and there are no secondary microspheres. When ethyl acetate is used for etching for 10 min, the hollow SiO₂ microspheres with the diameter of 1 570 nm and thickness of 65 nm are prepared. Moreover, micron-sized SiO₂ hollow microspheres are self-assembled into photonic crystal materials by a vertical deposition method. As the concentration of self-assembly solution increases, the arrangement of SiO₂ hollow microspheres is tightly ordered without obvious vacancies and with a hexagonal periodic structure. The number of layers increases from 6 to 16, and the reflectivity gradually increases. When the solubility of the self-assembled solution is 0.005 g/mL, the maximum reflectivity is 85%.

The micron-sized SiO₂ hollow microspheres with a good dispersion, a high uniformity, a less damage, and a high sphericity were prepared by a template encapsulation method and an ethyl acetate etching process. Also, micron-sized SiO₂ hollow microsphere photonic crystals with a good thermal insulation performance, a low density, and a reflectivity of 85% as infrared band hollow microsphere photonic crystals were prepared by a vertical deposition self-assembly method.

Ti-Mn hydrogen storage alloys are practically applied in the field of compressed hydrogen storage due to their advantages of low cost, satisfying dynamics, high hydrogen storage capacity and cycling stability. It is necessary for the further development and application of Ti-Mn hydrogen storage alloys to specifically investigate the bonding of hydrogen atoms with metal atoms as well as the distribution of hydrogen atoms. However, it is difficult to utilize the micro-scale analysis of X-ray diffraction and transmission electron microscopy to achieve this goal. Therefore, some cutting-edge characterization tools, such as differential phase contrast (DPC) imaging, can be used to accurately characterize the positions of interstitial hydrogen atoms as well as the hydrogen binding energies at different positions, which is a key to understanding the hydrogen storage mechanism and chemical properties of metal hydrides. It should not be ignored that the cost issues also need to be considered in the application. At present, the commonly used methods are vacuum self-consuming electrode or induction melting followed by heat treatment to achieve the homogenization of the sample composition. Hence, there is an urgent need to further explore the methods for low-cost and large-scale preparation of Ti-Mn system hydrogen storage alloys in the future.

Hydrogen energy, as an environmentally friendly and clean energy source, is expected to optimize the energy structure and alleviate energy consumption due to its high energy density, good combustion characteristics and abundant reserves. Hydrogen production from photolyzed water is considered as the most ideal way to obtain hydrogen source in the future. However, the disadvantages of weak visible light response, low catalytic activity, and poor chemical stability are one of the main factors limiting the application of traditional photocatalytic materials in photolytic water hydrogenation to real life. Zinc indium sulfide (ZIS) is proved to be an ideal semiconductor photocatalyst due to its good chemical stability, moderate forbidden bandwidth (2.2-2.5 eV), suitable conduction band position (-0.79 eV), and good visible light absorption (absorption edge about 540 nm). However, ZIS suffers from a high photogenerated carrier complex rate and a weak photostability. Scholars optimized the ZIS energy band structure, expanded the spectral absorption range, improved the photoelectron dynamics behavior, and enhanced the photostability of ZIS by different approaches like morphology regulation, elemental doping, co-catalysis, and heterojunction. S-type heterojunctions have attracted recent attention due to their excellent photogenerated carrier dynamics and highly efficient photodissociation of hydrogen from water. In this paper, CWO/ZIS composite nanomaterials were synthesized by a two-step hydrothermal/water-bath method, and the photocatalytic mechanism of CWO/ZIS heterojunctions was discussed via constructing S-type heterojunctions, using the built-in electric field to enhance the photogenerated electron/hole separation efficiency and the migration rate.

Cobalt tungstate (CWO) nanoparticles were firstly prepared by a hydrothermal method, and then S-type CWO/ZIS heterojunctions were prepared by a water bath method. The composite samples named as CWO/xZIS were prepared at different molar ratios of Co²⁺ to Zn²⁺ (i.e., x = 0, 1%, 2%, 3%, 4%, 5%, 6%, and 10%). The properties of the samples (i.e., physical phase components, morphology, crystal structure, elemental distribution, chemical state, photocatalytic hydrolysis performance, photogenerated carrier separation efficiency, photogenerated charge transport rate, and photogenerated electron/hole pair recombination rate) were characterized.

The photocatalytic hydrogen production performance of the samples was tested by a 30 mL customized photoreactor and a Timex GC7900 gas chromatograph. A 300 W Xenon lamp was equipped with a cut 420 nm filter (wavelength range: 420-780 nm) and an all-reflector was used as a visible light source. 5 mg of the sample was added to a mixed solution containing 9 mL of deionized water and 1 mL of triethanolamine (TEOA) and transferred to a 30 mL photoreactor sealed well. The air in the reactor was removed via charging the reactor with argon gas for 10 min. Afterwards, the reactor was mounted on the reaction platform, the circulating cooling water was turned on, the temperature of the reaction system was controlled at 10 ℃, and a stirrer was used for continuous stirring. A Xenon lamp 10 cm away from the reactor was turned on for illumination, and 100 μL of gas was extracted from the reactor for each 30 min and injected into the gas chromatograph for gas analysis for 3 h. The cyclic experiments were repeated under the same conditions for several times.

According to the experimental results by X-ray diffraction (XRD), pure ZIS and pure CWO samples can be prepared. The characteristic peaks of ZIS and CWO both appear in the XRD patterns of the CWO/xZIS sample, indicating that CWO and ZIS are compounded. The surface morphology and microstructure of pure ZIS, pure CWO nanomaterials and their composite samples are determined by field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). Based on the FESEM images, pure ZIS appears a typical two-dimensional nanosheet structure, and the size of pure CWO nanoparticles is approximately 50 nm. The FESEM images of CWO/3%ZIS samples show that CWO nanoparticles are attached to ZIS nanosheets. The HRTEM images show that the coexistence of lamellar and granular forms on the CWO/3%ZIS sample occur, confirming that the product contains both CWO and ZIS. Two sets of different lattice stripes corresponding to different crystalline surfaces of pure ZIS and CWO appear in the product, which further confirms that CWO and ZIS are composited. The X-ray photoelectron spectra indicate that CWO/3%ZIS samples contain ZIS and there is astrong intense interaction between CWO and ZIS.

From the results of hydrogen production tests on CWO/xZIS samples, the samples of CWO/3%ZIS show the maximum hydrogen production activity with a photocatalytic hydrogen production rate, which is twice greater than that of pure ZIS. The reproducibility test proves that the samples of CWO/3%ZIS have a good photochemical stability. From the results of electrochemical performance tests on different samples, CWO/3%ZIS sample has the maximum photocurrent density and the minimum electrochemical impedance, thus indicating that it has the maximum photogenerated carrier separation efficiency and transport rate, which is also consistent with the photocatalytic hydrolysis to production hydrogen performance.

Pure CWO nanoparticles were synthesized by a hydrothermal method and S-type CWO/ZIS heterojunctions were prepared via loading CWO nanoparticles onto ZIS nanosheets by a water bath method. The results of XRD, FESEM, HRTEM, and XPS confirmed the formation of a close contact between CWO and ZIS and the construction of a good heterogeneous interface. The results of visible-light water splitting hydrogen production tests showed that the hydrogen production performance of the CWO/xZIS composite samples was improved, compared with that of pure ZIS, in which the hydrogen production rate of the CWO/3%ZIS samples reached 4 296.8 μmol·g^-1·h^-1, which is twice greater than that of pure ZIS (i.e., 2 178.2 μmol·g^-1·h^-1). The electrochemical performance test results showed that the S-type heterojunction photogenerated carrier transport channel was constructed due to the well-matched energy band structures of CWO and ZIS, resulting in the composite samples with a higher separation efficiency of the photogenerated electron/hole pairs, a faster photogenerated charge transport rate, and a smaller electron/hole recombination rate, thus leading to the enhancement of the photocatalytic hydrolysis into hydrogen generation efficiency of the CWO/xZIS heterojunction.

In recent years, 5G communication and smart devices become popular, but the electromagnetic pollution that they produce affects human-being health and the normal operation of electronic devices. Therefore, electromagnetic wave strong attenuation materials have attracted much attention, especially polymer-derived ceramics (PDCs) due to their tunable microstructure and superior high-temperature performance. The amorphous structure of the ceramics has a high-temperature stability, but the dielectric constants are low, making them weak to electromagnetic wave dissipation. To address this problem, catalysts for increasing heat treatment temperature or direct addition of high conductive loss phases (CNTs, RGO, etc.) are usually used to improve the attenuation ability of the ceramics to electromagnetic waves. Rare-earth element metals can modulate the electronic energy band structure of the materials due to the presence of empty d-orbitals, thus modulating their optical, electrical, and magnetic properties. In this paper, the effect of samarium doping on the microstructure and dielectric properties of SiBCN ceramics was thus investigated via introducing the transition metal Sm into polyborosilazane as a catalyst.

Based on the 'Schlenk' technology, 20 mL THF, 21 mL DCMVS and 24 mL borane dimethyl sulfide complex were slowly added to a reaction bottle in an ice bath, and the reaction was carried out in argon atmosphere for 24 h to obtain dichlorodimethylsilylethylborane (TDSB). Afterwards, 11 mL DCMS and 72 mL HMDZ were stirred in a three-neck flask at room temperature for 24 h. The reaction bottle was heated at 110 ℃ for 4 h to remove THF, trichloromethylsilane and other by-products, and was further heated at 170 ℃ for 3 h. After three cycles of filtration, a yellow viscous precursor was obtained. To obtain Sm-containing polyborosilazane, PBSZ was weighed and dissolved in THF before SmCl₃ dissolving in DMF was added. The precursors without and with different SmCl₃ mass fractions of 0, 1% and 3% were named as samples PS0, PS1 and PS3. The PBSZ was slowly heated in a tube furnace (TL1700, Nanjing Boyuntong Co., Ltd., China), in argon atmosphere at 180 ℃ for 1 h, and then further heated at 400 ℃ for 3 h to obtain a cured PBSZ. The cured PBSZ was ground and cold-pressed into φ20×2 mm wafers at 80 MPa. SiBCN ceramics were acquired via heating the wafers in argon atmosphere at 1 000 ℃ for 1 h in, and then further heated at 1 600 ℃ for 2 h.

The physical phase composition of the ceramics was determined by a model X'Pert MPD Pro X-ray diffractometer (XRD, The Netherlands) with Cu target at a tube voltage of 40 kV and a tube current of 30 mA. The elemental species, atomic valence states, and binding states of SiBCN ceramics were analyzed by a model AXIS SUPRA+ X-ray photoelectron spectroscope (XPS, Shimadzu Co., Japan). The microstructure and morphology were determined by a FEI NOVA 400 scanning electron microscope (SEM, USA). The microstructure and distribution pattern of the ceramics were characterized by a model JEM-F200 transmission electron microscope (TEM, Japan). The oxidation resistance of SiBCN ceramics was determined by a model STA 449F3 thermogravimetric analyzer (TG, Netzsch Co., Germany) in air at a heating rate of 10 ℃/min. The electromagnetic parameters of the ceramics were determined by a model Keysight E5071C vector network analyzer (Malaysia).

Sm doping promotes the increase of dielectric crystals such as SiC and SiCN in the ceramics. This is due to the better promotion of polymer ceramic crystallization by transition metals. The optimum oxidation resistance of the ceramics is obtained at Sm doping of 1%. The BN phase generates a great mass of B₂O₃ during high temperature oxidation due to the massive crystals generated, which is closer to the oxidative weight loss of free carbon. Also, B₂O₃ forms a liquid-phase protective layer that covers the ceramic surface and prevents a further diffusion of air into the interior of the material, improving the material antioxidant properties.

The superior impedance matching is obtained and the absorption performance of the ceramics for electromagnetic waves is enhanced due to the generation of dielectric crystals such as SiC and SiCN. At Sm doping of 1%, the ceramics have the optimum attenuation performance for electromagnetic waves due to the presence of conductivity loss and polarization loss in SiBCN ceramics, and the maximum attenuation constant α. When the thickness is 2 mm, the ceramic achieves the RA_min of -40.00 dB at 17.36 GHz and the effective absorption bandwidth (EAB) of 5.12 GHz.

The generation of SiC, SiCN and Si₃N₄ crystals was promoted by Sm doping, and the intensity of diffraction peaks of each crystal phase increased with the increase of Sm doping. The generation of SiC and SiCN dielectric crystals and their heterogeneous interfaces enhanced the attenuation performance of SiBCN ceramics against electromagnetic waves. The RAmin of the ceramics reached -40.00 dB at 17.36 GHz with an EAB of 5.12 GHz at a thickness of 2 mm.

The existing research on hydrogen electrode materials for SOEC involved the systematic theoretical and experimental studies. To commercialize hydrogen production through SOEC, it is still necessary to further investigate hydrogen electrode materials. At the mechanistic level, advanced characterization techniques, such as in-situ transmission electron microscopy and X-ray photoelectron spectroscopy, combined with first-principles calculation and distribution of relaxation time method, can be employed to investigate the reaction mechanisms of SOEC hydrogen electrodes. This approach guides subsequent development and application of electrode materials. The degradation of hydrogen electrode materials is a primary obstacle to the current commercialization of SOEC. The existing research predominantly focused on Ni-based metal ceramic hydrogen electrodes. For Ni-based metal ceramics, the main issues involve the oxidation, migration, and coarsening of nickel. Based on the fundamental mechanisms of electrode reactions, a comprehensive exploration of material degradation phenomena and their mechanisms is conducted. The severity of the impact of the mentioned changes on the elementary reactions of the electrode is assessed, and the corresponding improvement strategies are proposed. At the material level, it is essential to conduct in-depth studies based on the actual requirements of the electrodes. Combining theoretical predictions with experimental data, some performance-enhancing novel hydrogen electrode materials can be obtained through ion doping and in-situ exsolution for the regulation of electronic structure, charge carrier migration capability, and surface oxygen vacancy formation energy. At the application level, improvements in large-scale cell manufacturing process, optimization of the microstructure of Ni-YSZ electrodes, and the incorporation of high-performance catalytic materials such as perovskites using methods like ion liquid injection are crucial for advancing the practical application of SOEC.

Underground coal gasification (UCG) technology is critical to coal development in China, which has attracted recent attention. UCG technology can directly convert coal into syngas rich in CH₄, H₂, CO₂, and CO beneath the earth surface, which is appropriate for the employment of coal resources with a low value (i.e., coal resources in large depths or with restricted thickness). UCG technology significantly reduces the economic cost and safety risks of coal mining and improves the overall efficiency of coal utilization. Syngas obtained from UCG technology is used to produce higher-value-added chemicals, such as methanol, ammonia, ethylene, and Fischer-Tropsch synthesis products, and the fuel for heating and power generation. Using syngas produced by UCG technology for power generation is mainly carried out through internal combustion engines. The energy conversion efficiency is limited by the Carnot cycle, usually about 30%, which diverges from the goal of clean and efficient use. Solid oxide fuel cells (SOFCs) convert the chemical energy in syngas fuel directly into electrical energy through electrochemical reactions. The conversion efficiency is considerably high and is not limited by the Carnot cycle. Power generation efficiency of > 60% and combined heat and power (CHP) efficiency of > 90% can be achieved. Therefore, SOFCs can efficiently employ the syngas from UCG, which is important for the clean and efficient development and utilization of coal. Flat-tube SOFCs exhibit high thermal shock resistance and stability under the redox cycle and are capable of being used in harsh environments. This paper was to investigate power generation using flat-tube SOFCs fed with carbon-containing fuels. In addition, the performance and durability of anode-supported flat-tube SOFCs with direct internal reforming of syngas from UCG were also analyzed.

The flat-tube Ni/yttria-stabilized zirconia (YSZ) anode-supported cell contains a porous NiO-3YSZ (3% yttria-stabilized zirconia, in mole fraction, ~1 mm thick) anode support, a NiO-8YSZ (8% yttria-stabilized zirconia, in mole fraction, 15-20 μm thick) anode functional layer, a dense 8YSZ electrolyte layer (15-20 μm thick), a gadolinia-doped ceria (GDC) barrier layer (~3 μm thick), and a porous (La_0.6, Sr_0.4)(Co_0.2, Fe_0.8)O₃) (LSCF)-GDC cathode layer (15-20 μm thick). The cell was indicated as NiO-3YSZ|NiO-8YSZ 8YSZ|GDC|LSCF-GDC. The cell dimensions were 155 mm × 65 mm × 5.5 mm with an active cathode area of 60 cm². The cell was heated in air at 750 ℃ after assembly. The anode was reduced under 0.3 L·min^-1 H₂ prior to the electrochemical tests. H₂ or syngas was fed to the anode to evaluate the cell performance. To evaluate the electrochemical cell performance, the open-circuit voltage (OCV), current-voltage (I-V) characteristics, and electrochemical impedance under different conditions were measured by a model VMP3B-20 electrochemical workstation (BioLogic Co., France). The electrochemical impedance spectra (EIS) were recorded under OCV condition in the frequency range of 30 mHz to 30 kHz at an alternating current of 10 mV.

The increasing temperature reduces a carbon deposition in SOFC fueled with different syngas. Especially at 750 ℃, the carbon deposition is not favorable for most types of UCG syngas. When the flow rates of H₂, CO, CH₄, and CO₂ are fixed, the composition of N₂ does not affect the carbon deposition. Increasing the composition of CO₂ mitigates the carbon deposition. The power density of SOFC with H₂ at 750 ℃ is 260.3 mW·cm^-2 at 0.8 V, and the maximum power density is 395.1 mW·cm^-2. The power density of a cell fueled with syngas (Swan Hills) at 0.8 V is 240.1 mW·cm^-2, and the maximum power density is 361.9 mW·cm^-2, reaching 91.6% of that with H₂. The power densities of SOFC fueled with other types of UCG syngas are lower than those fueled with syngas (Swan Hills). The stability test of the flat-tube SOFCs fed with syngas (Swan Hills) is conducted at 750 ℃ under 300 mA·cm^-2. During the test, the composition of CO₂ is changed. The flat-tube SOFC can discharge stably for 960 h. When the CO₂ content is higher than or equal to 20% (in volume fraction), the degradation rate is less than 2.7% every 100 h in each stage. No sudden performance degradation emerges, indicating that the flat-tube SOFCs can run stably under such conditions. Since the original composition of syngas (Swan Hills) is similar to that of stage 2 (for 112-214 h), a stable power generation from flat-tube SOFCs directly using UCG syngas (Swan Hills) is viable. The CO₂ content reduces to 10% at approximately 460 h. The voltage fluctuates sharply at 520 h. Subsequently, when CO₂ further decreases to 0, the cell operates stably for another 144 h. However, when N₂ flow is stopped at 750 h, the performance deteriorates significantly. After the long-term test, two characteristic peaks of carbon deposition appear in the Raman spectrum, i.e., the D peak (at 1 335-1 350 cm^-1) and the G peak (at 1 580-1 600 cm^-1). The result indicates that the carbon deposition is formed on the surfaces of the fuel channels. The SEM images show that after the test at 960 h, a significant Ni particle agglomeration occurs in the active anode layer of the cell fed with syngas (Swan Hills), and the average Ni particle size is increased by 17.0%. The Ni content loss in the active anode layer appears. Especially, the Ni content near the electrolyte layer (0-5μm) decreases from 30.0% (pixel, same below) to 19.2%. Carbon deposition, nickel agglomeration, and nickel particle loss result in a performance degradation.

The cell performance and durability of flat-tube solid oxide fuel cells by direct internal reforming of syngas from underground coal gasification were investigated. The peak power density of the cell with syngas (Swan Hills) from underground coal gasification was 361.9 mW·cm^-2 at 750 ℃ (Note: Swan Hills is a coal mine in Canada), which was approximately 91.6% of that with H₂. Astable operation with a constant current of 300 mA·cm^-2 at > 960 h was realized. The ohmic resistance and polarization resistance increased from 0.108 Ωcm² and 0.485 Ω·cm² to 0.190 Ω·cm² and 0.494 Ω·cm², respectively. The increased rates of the ohmic resistance and polarization were 0.085 Ω·cm²·kh^-1 and 0.009 Ω·cm²·kh^-1, respectively. The main degradation mechanisms were the carbon deposition on the anode, Ni percolation loss, and Ni particle agglomeration, detected by Raman spectroscopy and scanning electron microscopy. Elevating CO₂ concentration suppressed the carbon deposition, improving the cell stability.

As a positive material with a low cost, a high energy density and a good power performance, spinel lithium manganese nickel oxide (LiNi_0.5Mn_1.5O₄) has attracted much attention in the industry of lithium ion battery. Reducing the surface oxygen release behavior and the resolution of Ni or Mn during charging and discharging is a main method to improve the electrochemical performance. The conventional coating technique is to construct a coating layer on the surface of the material particles, which can isolate the electrolyte and reduce side reactions at the interface. Since the solid-phase coating method cannot form the uniform and compact coating layer, the improvement of the electrochemical performance is limited. In this paper, a precursor with Li₃PO₄ layer that was produced by a wet coating method was sintered at 850 ℃. In addition, the impact of coating method was also analyzed by the first-principles calculation and characterizations.

According to a molar ratio of LiNi_0.5Mn_1.5O₄, a certain amount of Ni_0.25Mn_0.75(OH)₂ precursor and Li₂CO₃ were weighed and mixed. The mixed material was ground in a mortar evenly. Afterwards, the ground material was sintered in a muffle furnace at 950 ℃ for 10 h, finally obtaining a LNMO positive electrode material (i.e., sample P0) after cooling in the furnace.

According to the designed coating amount of 3% Li₃PO₄, NH₄H₂PO₄ and LiOH·H₂O were weighed and sequentially added to alcohol solution with LNMO particles. After stirring and evaporation, the collected products were sintered in a muffle furnace to obtain conventional coating LNMO@Li₃PO₄ material (i.e., sample P1).

Also, Ni_0.25Mn_0.75(OH)₂ precursor was mixed with deionized water in a mass ratio of 1∶5. LiOH·H₂O was added to the coating at 3% under stirring until fully dissolved. Also, NH₄H₂PO₄ was added in another beaker and mixed with deionized water in a mass ratio of 1∶20 until fully dissolved. The above two solutions were mixed thoroughly and filtered. The obtained filtered product was dried in a blast drying oven at 90 ℃ for 24 h to obtain Ni_0.25Mn_0.75(OH)₂ precursor pre-coated with Li₃PO₄. Li₂CO₃ in a ratio of Li:(Ni+Mn) of 1∶2 was mixed evenly with the pre-coated precursor, and heated in a furnace at 950 ℃ for 10 h to obtain a wet coated LNMO cathode material with Li₃PO₄ after cooling (i.e., sample P2).

The morphologies and structures of the cathode materials were examined by a model S-4800 scanning electron microscope (SEM, Hitachi Co., Japan) a model F20 aberration-corrected transmission electron microscope (TEM) with a cold field emission gun at 200 kV (TECNAI), and a model Panalytical X'Pert X-ray diffractometer (XRD) in the 2θ range of 10°-75° with Cu K_α radiation (λ=1.540 5 Å). The compositions of TMs in materials were measured by a model IRIS IntrepidⅡinductively coupled plasma atomic emission spectroscope (ICP-AES, XSP).

Density functional theory (DFT) calculations were carried out through a named Vienna ab initio package (VASP), in which the cut-off energy was set to 520 eV for an accurate test, and the projector augmented wave (PAW) was used to describe the interaction between ions and electrons. For the optimization of crystal structures, the exchange correlation function was used as the Perdew-BurkesEmzerhof (PBE) form of generalized gradient approximation (GGA). The lattice vector and the atomic position were sufficiently optimized until the resultant force was less than 0.01 eV/(Å·atom^-1). The Brillouin zone was adopted with a 4×4×4 k-mesh.

Each material was mixed with carbon black and polyvinylidene fluoride binder in N-methyl-2-pyrrolidone with a mass ratio of 90∶5∶5 to prepare the electrode slurry. Subsequently, the slurry was casted on the Al foil and dried in vacuum at 100 ℃. Pouch cells were assembled with graphite as an anode, and 1 mol/L LiPF6 solution in EC/EMC/DEC (3∶5∶2 by volume) as an electrolyte. Pouch cells were tested at 3.50-4.95 V and 0.1 C (1 C=150 mA·h·g^-1) for the first cycle on a model Maccor S4000 battery testing system. The cycling performance, EIS, and rate capability at 25 ℃ were tested at 3.5-4.9 V.

Based on the powder XRD patterns of samples P0, P1, and P2, all the samples have a typical spinel structure, since the Li₃PO₄ coating layer has no impact on the LNMO's crystal structure. The SEM images of samples reveal that the coating process has a slight effect on the surface appearance and particle size distribution. Based on the TEM and SEM-EDS analysis, the coating layer of sample P2 has higher homogeneity than that of sample P1, which can provide a better protective effect and reduce the corrosion of the electrolyte. According to the cycling data, the capacity retention is 90.47%, which is obvious improvement from sample P0 after running 300 cycles, and the superior cycling performance indicates an outstanding structural stability of sample P2, which can be proved by the Mn dissolution data. The capacity retention of 92.45% at 2C discharging can verify that sample P2 has a uniform coating layer. As a result, the precursor pre-coating Li₃PO₄ technique affects the phase structure and morphology of spinel LNMO slightly, and improves the electrical properties effectively.

The main phase structure and micromorphology of spinel LNMO remained unchanged after Li₃PO₄ coating, and the characteristic peak of Li₃PO₄ appeared. The rate discharging and cycling performance was significantly improved, and the charge transfer impedance was reduced by Li₃PO₄ layer. This study indicated that precursor pre-coating Li₃PO₄ technique could be an effective approach to reduce the dissolution of transition metal and could be thus a potential method to improve the electrochemical performance of lithium manganese nickel oxide.

In recent years, heat accumulation occurs with the emergence of the "heat island effect". The high temperature can affects human living environment, and increases the energy consumption of refrigeration equipment. It is thus necessary to develop color thermal insulation materials with a high near-infrared reflectance. The existing components used for insulation coatings are mostly rare-earth transition metal composite oxides. However, a higher cost of using rare earth materials restricts the large-scale application to some extent. Transition metal high-entropy ceramic inorganic powder can be used as cheap raw materials, which has the advantages of multi-component characteristics (i.e., great component adjustment space, unique entropy effect, and adjustable material properties. However, little work on the use as high reflective pigments has been reported yet. In this paper, high-entropy ceramic carbonate powders were prepared and the color of the powders was innovatively adjusted via changing the transition metal components. In addition, the phase, color and optical reflection properties of the prepared high-entropy ceramic carbonate powders with different element combinations were also analyzed.

For the hydrothermal preparation of high-entropy carbonate powders (i.e., (Mg_0.2Co_0.2Ni_0.2Zn_0.2Cu_0.2)CO₃, (Mg_0.2Co_0.2Ni_0.2Zn_0.2Fe_0.2)CO₃, and (Mg_0.2Co_0.2Ni_0.2Zn_0.2Mn_0.2)CO₃), pure MgSO₄, CoSO₄, NiSO₄, ZnSO₄, FeSO₄, MnSO₄, CuSO₄ and Na₂CO₃ were used as raw materials according to a stoichiometric coefficient ratio. Firstly, a certain proportion of five metal sulfate solids was mixed with deionized water in a beaker under stirring until fully dissolved. The sulfate solution was put into a sodium carbonate solution, and mixed under stirring. Afterwards, the mixture in a high-pressure reactor with a PTFE lining was heated at 160 ℃ for 12 h for hydrothermal treatment. A high-entropy carbonate powder was obtained after centrifugation, washing, and drying.

The phase composition of the powder was determined by a model Empyrean X-ray diffractometer (XRD, PANalytical Co., The Netherlands). The microstructure of the powder was analyzed by a model SUPRA 55 field emission scanning electron microscope (FESEM, Carl Zeiss Co., Germany). The UV visible near-infrared diffuse reflectance of the powder was characterized by a model LAMBDA 750 ultraviolet-visible-near infra-red spectrometer (UV-VIS-NIR, PerkinElmer Co., USA). The near-infrared solar reflectance R* in the wavelength range of 780-2 500 nm was calculated according to the national standard ASTMG159-98. The L*a*b* color parameters of the powder were determined by a model CS-5960GX spectrophotometer.

Three types of five-component equimolar high-entropy carbonate solid solutions were prepared by a hydrothermal method. Based on the morphology characterizations, three high-entropy carbonates synthesized have the same crystal structure and the same spatial group as . The diffraction peak gradually shifts towards a lower diffraction angle with the order of the components Cu, Fe, and Mn. This is because the radius of the element ions gradually increases, resulting in a corresponding increase in the crystal plane spacing. Moreover, there are significant differences in the morphology characteristics of three high-entropy carbonates, which are the result of the multiple effects of factors such as the number of extranuclear electrons, the Jahn Teller distortion, magnetism, and bond length of Cu, Fe, and Mn ions. The Jahn Teller distortion and para-magnetism of Cu lead to the formation of irregular spherical particles with surface density and particle aggregation in the MgCoNiZnCu carbonate solid solution. The ferromagnetism of Fe causes MgCoNiZnFe carbonate solid solution to form the spheres with dense and regular surface morphology. The combination of ion bonding bond length and antiferromagnetism of Mn results in the formation of loose aggregates of MgCoNiZnMn carbonate solid solutions. In addition, the colorimetric characterization indicates that the color of three high-entropy powders is different (i.e., grayish green for MgCoNiZnCu, orange red for MgCoNiZnFe, and light purple for MgCoNiZnMn). The band gap value Eg gradually increases with the order of the component Fe, Cu, and Mn, and the absorption wavelength of the sample gradually decreases (i.e., the absorption wavelengths are 497.14, 393.99 nm and 242.71 nm, respectively), and the absorption edge gradually shifts blue. Three types of high-entropy carbonate solid solutions have a high near-infrared solar reflectance in the near-infrared band, with a maximum of 78.64%, which can be used as thermal insulation materials.

Three high-entropy carbonate powders with different elemental compositions were prepared by a hydrothermal method, and the phase composition, reflectance, and color properties of the synthesized powders were comprehensively investigated. The results showed that changing a single element in the compositions could change the color of the powder (i.e., grayish green for MgCoNiZnCu, orange red for MgCoNiZnFe, and light purple for MgCoNiZnMn), and the color coordinate L*a*b*c* value also changed accordingly. Meanwhile, the bandgap width of the powder gradually increased from 3.11 eV to 3.40 eV and 5.49 eV with the order of the component Fe, Cu, and Mn. The three compositions of high-entropy carbonate powders had three different shades in the visible light region, and a high near-infrared solar reflectance (R*) of 78.64%. Therefore, the high-entropy carbonate powders prepared via changing the component element had the characteristics of stable structure, tunable color, and high near-infrared reflectance, having broad application prospects in architecture, automotive, and chemical engineering.