In Situ Electrochemical Mn(Ⅲ)/Mn(Ⅳ) Generation of Mn(Ⅱ)O Electrocatalysts for High-Performance Oxygen Reduction

Among various earth-abundant and noble metal-free catalysts for oxygen reduction reaction(ORR),manganese-based oxides are promising candidates owing to the rich variety of manganese valence.Herein,an extremely facile method for the synthesis of cubic and orthorhombic phase coexisting Mn(Ⅱ)O electrocatalyst as an efficient ORR catalyst was explored.The obtained MnO electrocatalyst with oxygen vacancies shows a significantly elevated ORR catalytic activity with a half-wave potential(E1/2) of as high as 0.895 V,in comparison with that of commercial Pt/C(E1/2=0.877 V).More impressively,the MnO electrocatalyst exhibits a marked activity enhancement after test under a constant applied potential for 1000 s thanks to the in situ generation and stable presence of high-valence manganese species(Mn^3+ and Mn^4+) during the electrochemical process,initiating a synergetic catalytic effect with oxygen vacancies,which is proved to largely accelerate the adsorption and reduction of O_2 molecules favoring the ORR activity elevation.Such an excellent ORR catalytic performance of this MnO electrocatalyst is applied in Zn-air battery,which shows an extra-high peak power density of 63.2 mW cm^-2 in comparison with that(47.4 m W cm^-2) of commercial Pt/C under identical test conditions.

Synthesis of High Surface Area and Well Crystallized Mesoporous WC at Low Temperature with a Pore Structure Collapsed Replication Route

An approach named ＂pore structure collapsed replication route＂ has been developed to prepare mesoporous WC materials with a high surface area （105 m2/g） and crystallized framework at a temperature as low as 700 ℃. The XRD, TEM, EDS, and BET characterizations were conducted to analyze the effects of the synthesis parameters and the template types on the structure of mesoporous WC. The compaction on the templates is the key to form mesoporous structure of WC while the templates help to control the size of crystalline. At a content of 7 wt% for the precursor of WC, the mesoporous WC could be formed with well ordered structure.

Defects Formation and Morphology in Large-sized MoSi_2 Rod Prepared by Continuous Extrusion

Incidence of defects in MoSi2 rods prepared by con- tinuous extrusion is dependent on the viscosity of binder. Generally, low viscosity results in surface defects while high viscosity is responsible for inner defects. Cross-section observations indicated that the typical inner defects in sintered MoSi2 rods were large fissure cavity, multiple small holes and single small cavity, of which the characteristic ultrasonic reflection patterns have been experimentally established. Formation of the inner defects is attributed to the inhomogeneous feedstock moving behav- ior in die, which is aggravated with increasing viscosity of binder. Defect free MoSi2 rods were prepared successfully via con. tinuous extrusion by carefully controlling the viscosity of binder.

Preparation and Luminescence Properties of Gadolinium Aluminate Phosphor Material Chip

The combinatorial material chip approach is an excellent innovation for inorganic functional material research, and it can discover and screen new materials efficiently. In the present work, the approach was used to find quickly and improve gadolinium aluminate phosphors (Gd_ 1-xAl_yO_z∶RE_x). Under UV lamp excited (λ_ ex=254 nm) the Gd_ 1-xAl_yO_z∶RE_x phosphor material chip evaluation shows that the suitable n(Al)∶n(Gd) in host materials is 1∶1 for Eu and Tb ion activators. The luminescence character coherence between combinatorial material chip and parallelism powder samples produced by nitric-citric process was also confirmed.

Luminescence Spectra of YGG：RE^3＋, Bi^3＋ （RE = Eu and Tb） and Energy Transfer from Bi^3＋ to RE^3＋

We investigate the luminescence properties of Bi^3＋ and RE^3＋ （RE = Tb or Eu） in a Y3Ga5O12 （YGG） host system. The additional doping of Bi^3＋ can enhance the luminescence of Th^3＋ or Eu^3＋ in this host. Energy transfer from Bi^3＋ to Tb^3＋ and Eu^3＋ is observed and the mechanism of energy transfer is investigated. Mechanism of energy transfer can be explained as electric multipole interaction since the Bi^3＋ emission band and Tb^3＋ or Eu^3＋ excitation band overlaps and the Bi^3＋ emission intensity decreases while the intensity of Tb^3＋ or Eu^3＋ increases with the increase of Tb^3＋ or Eu^3＋ concentration. Therefore, Bi^3＋ ion is a kind of efficient sensitizer to the Tb^3＋ and Eu^3＋ activators in the Y3Ga5O12 host.

Effect of melt pulse electric current and thermal treatment on A356 alloy

Effects of the melt pulse electric current and thermal treatment on solidification structures of A356 alloy were investigated. In the experiments, the low temperature melt(953 K and 903 K) treated by pulse electric current was mixed with high temperature melt(1 223 K). By the control experiments, the results show that the solidification structure of A356 alloy is refined apparently by the pulse electric current together with melt thermal treatment process, and the mechanical properties, especially the elongation ratio of the specimen treated is improved greatly. The structure change of the melt by pulse electric current and melt thermal treatment is the main reason for the refinement of the solidification structure of A356 alloy.

Thermodynamics of some ZrO_2-containing ceramics

Thermodynamic assessment in the ternary systems ZrO2 -CeO2 -Y2 O3, ZrO2 -CeO2 -Ce2 03 and the limiting binaries ZrO2 -Y2 O3, ZrO2 -CeO2, CeO2 -Y2 03, ZrO2 -Ce2O3, CeO2 -Ce2O3 as well as the modeling for oxides are reviewed comprehensively. Based on the recent estimations on the YO1.5-CeO2, ZrO2-CeO2 and ZrO2 -YO1.6 systems, isothermal sections at 1273 and 1 973 K of the ternary CeO2- ZrO2-YO1.5system are calculated. In the system of ZrO2-CeO2-Ce2O3, the complex relation between the nonstoichiometry （y） in CeO2-x, the composition of the ZrO2 -CeO2 solid solution and the oxygen partial pressure （Po2 ） for different ZrO2 containing solid solutions CexZr1-xO2-x. are evaluated from 1 473 to 1 773 K. The relation between the degree of Ce^＋4 reduction to Ce.3 under different Po2 in the fluorite CeO2-xy and CexZr1-xOz-x solid solutions at different temperatures can be used as a guide in the development of functional ceramics.

Synthesis, Crystal Structure, Fluorescent and Thermal Properties of Sodium Tridecafluorodizirconate Na_5Zr_2F_(13) Compound

Crystals of sodium tridecafluorodizirconate Na5Zr2F13 were synthesized under mild hydrothermal conditions, and the structure was refined by single-crystal X-ray diffraction. The compound crystallizes in monoclinic with crystallographic data： Mr = 544.39, C2/m （No. 12）, a = 11.5600（9）, b = 5.4759（4）, c = 8.3989（6） A°, β = 97.361（10）°, V= 527.28（7） A°^3, Z= 2, Dc = 3.429 g/cm^3, 2 = 0.71073A° ,μ = 23.48 cm^-1, F（000） = 504, T= 295 K, Ri = 0.0173 and wR2 = 0.0449 for 55 variables and 682 contributing uniqUe reflections. The crystal structure is constituted with sixand eight-fold sodium atoms, forming irregular trigonal prisms and irregular cubes, respectively. Here, the zirconium atoms are connected with seven fluorine atoms to form a mono-capped trigonal prism. [Zr2F13]^5- complex ions formed by comer-shared [ZrF7]^3- are comer- and edgeshared to [Na4F22] and [Na3F8] cages, leading to the network structure. Thermal analysis, X-ray excited luminescence and photoluminescence under UV light measurements were conducted on Na5Zr2F13 crystals.

Improvement in Dielectric Tunability of Ba0.6Sr0.4TiO4-Mg2TiO4 Composite Ceramics via Heterogeneous Nucleation Processing

Dielectric tunable composite ceramics Ba0.6Sr0.4 TiO4-Mg2 TiO4 （BST-MT） are prepared with a heterogeneous nucleation sol-gel approach. The Mg2 TiO4 powders are synthesized by the conventionM solid-state reaction method. The micro-sized MT powders with dispersant Ciba-4010 are introduced into Ba-Sr-Ti sol to obtain uniform and homogeneous mixture compounds with nano-sized BST particles synthesized via heterogeneous nucleation （HN） in the sol-gel process. Thus, the mierostructural and dielectric properties can be tailored. The dielectric constants of BST-MT composite ceramics can be adjusted in a larg＇e range from 294 to 1790, and the dielectric tunability can be adjusted from 29.4% to 37.0% with different MT contents from 60wt% to 20wt%. Compared to the samples prepared by the conventional solid-state （SS） process, the BST-MT composite ceramics by the heterogeneous nucleation sol-gel process exhibit a more uniform microstructure, and improve dielectric properties.

Observation of Ferroelastic and Ferroelectric Domains in AgNbO_(3) Single Crystal

Compared to AgNbO_(3) based ceramics, the experimental investigations on the single crystalline AgNbO_(3), especially the ground state and ferroic domain structures, are not on the same level. Here, based on successfully synthesized AgNbO_(3) single crystal using a flux method, we observed the coexistence of ferroelastic and ferroelectric domain structures by a combination study of polarized light microscopy and piezoresponse force microscopy.This finding may provide a new aspect for studying AgNbO_(3). The result also suggests a weak electromechanical response from the ferroelectric phase of AgNbO_(3), which is also supported by the transmission electron microscope characterization. Our results reveal that the AgNbO_(3) single crystal is in a polar ferroelectric phase at room temperature, clarifying its ground state which is controversial from the AgNbO_(3) ceramic materials.

Hydrogen-assisted scalable preparation of ultrathin Pt shells onto surfactant-free and uniform Pd nanoparticles for highly efficient oxygen reduction reaction in practical fuel cells

Concentrating active Pt atoms in the outer layers of electrocatalysts is a very effective approach to greatly reduce the Pt loading without compromising the electrocatalytic performance and the total electrochemically active surface area(ECSA)for the oxygen reduction reaction(ORR)in hydrogen-based proton-exchange membrane fuel cells.Accordingly,a facile,low-cost,and hydrogen-assisted two-step method is developed in this work,to massively prepare carbon-supported uniform,small-sized,and surfactant-free Pd nanoparticles(NPs)with ultrathin~3-atomic-layer Pt shells(Pd@Pt_(3L) NPs/C).Comprehensive physicochemical characterizations,electrochemical analyses,fuel cell tests,and density functional theory calculations reveal that,benefiting from the ultrathin Pt-shell nanostructure as well as the resulting ligand and geometric effects,Pd@Pt_(3L) NPs/C exhibits not only significantly enhanced ECSA,electrocatalytic activity,and noble-metal(NM)utilization compared to commercial Pt/C,showing 81.24 m^(2)/gPt,0.710 mA/cm^(2),and 352/577 mA/mgNM/Pt in ECSA,area-,and NM-/Pt-mass-specific activity,respectively;but also a much better electrochemical stability during the 10,000-cycle accelerated degradation test.More importantly,the corresponding 25-cm^(2) H2-air/O_(2) fuel cell with the low cathodic Pt loading of~0.152 mgPt/cm^(2)geo achieves the high power density of 0.962/1.261 W/cm^(2)geo at the current density of only 1,600 mA/cm^(2)geo,which is much higher than that for the commercial Pt/C.This work not only develops a high-performance and practical Pt-based ORR electrocatalyst,but also provides a scalable preparation method for fabricating the ultrathin Pt-shell nanostructure,which can be further expanded to other metal shells for other energy-conversion applications.

Size effects of platinum particles@CNT on HER and ORR performance

Platinum(Pt)is an efficient catalyst for hydrogen evolution reaction(HER)and oxygen reduction reaction(ORR),but the debate of the relevance between the Pt particle size and its electrocatalytic activity still exist.The strong metal–support interaction(SMSI)between the metal and carrier causes the charge transfer and mass transport from the support to the metal.Herein,Pt species(0.5 wt.%)with various particle sizes supported on carbon nanotubes(CNTs)have been synthesized by a photo-reduction method.The^1.5 nm-sized Pt catalyst shows much higher HER performance than the counterparts in all pH solutions,and the mass activity of it is even 23–36 times that of Pt/C.While for ORR,the^3 nm-sized Pt catalyst exhibits the optimal performance,and the mass activity is 3 times and even 16 times that of Pt/C in acidic and alkaline media,respectively.The high HER and ORR performances of the^1.5 nm-and^3 nm-sized Pt catalysts benefit from the SMSI between Pt and the CNTs matrix and the higher ratio of face sites to edge sites,which is meaningful for the design of efficient electrocatalysts for renewable energy application.

Acoustic Imaging Frequency Dynamics of Ferroelectric Domains by Atomic Force Microscopy

We report the acoustic imaging frequency dynamics of ferroelectric domains by low-frequency acoustic probe microscopy based on the commercial atomic force microscopy. It is found that ferroelectric domain could be firstly visualized at lower frequency down to 0.5 kHz by AFM-based acoustic microscopy. The frequency-dependent acoustic signal revealed a strong acoustic response in the frequency range from 7kHz to 10 kHz, and reached maximum at 8.1 kHz. The acoustic contrast mechanism can be ascribed to the different elastic response of ferroelectric microstructures to local elastic stress fields, which is induced by the acoustic wave transmitting in the sample when the piezoelectric transducer is vibrating and exciting acoustic wave under ac electric fields due to normal piezoelectric effects.

Suppressing the donor-like effect via fast extrusion engineering for high thermoelectric performance of polycrystalline Bi_(2)Te_(2.79)Se_(0.21)

Bi2Te3-based alloys are the most mature commercial thermoelectric(TE)materials for the cooling application near room temperature.However,the poor mechanical properties of the commercial zone melting(ZM)ingot severely limits the further application.Meanwhile,due to the donor-like effect,the robust polycrystalline n-type bulks usually have low TE performance near room temperature.Herein,based on the commercial ZM ingots,a high figure of merit(zT)of 1.0 at 320 K and good mechanical properties are achieved via the hot extrusion.The dynamic recrystallization in the hot-extrusion process can suppress the donor-like effect and refine the large ZM grains into fine-equiaxed grains.Moreover,the obtained polycrystalline Bi2Te2.79Se0.21 has good preferential orientation and high carrier mobility(m).The high m and the weaken donor-like effect maintain the high power factor(PF)of 43.1 mW cm^(-1)K^(-2)in the hot-extruded ZM sample.Due to the enhanced phonon scattering,the total thermal conductivity ktot decreased to 1.35 W·m^(-1)·K^(-1).To demonstrate the good mechanical properties of the extruded ZM sample,micro TE dices with the cross sections of 300μm×300 mm and 200μm×200 mm are successfully cut from the extrusion sample.This study provided a fast and low-cost extrusion technique to improve the TE and mechanical properties of the commercial ZM ingot at room temperature.

Copper nanowire-TiO2-polyacrylate composite electrodes with high conductivity and smoothness for flexible polymer solar cells

Copper nanowire （Cu NW） transparent electrodes have attracted considerable attention due to their outstanding electrical properties, flexibility and low cost. However, complicated post-treatment techniques are needed to obtain good electrical conductivity, because of the organic residues and oxide layers on the surface of the Cu NWs. In addition, commonly used methods such as thermal annealing and acid treatment often lead to nanowire damage. Herein, a TiO2 sol treatment was introduced to obtain Cu NW transparent electrodes with superb performance （13 Ω/sq @ 82% T） at room temperature within one minute. Polymer solar ceils with excellent flexibility were then fabricated on the copper nanowire- TiO2-polyacrylate composite electrode. The power conversion efficiency （PCE） of the cells based on a blend of poly（3-hexylthiophene） （P3HT） and phenyl-C61- butyric acid methyl ester （PC61BM） reached 3.11%, which was better than the control devices that used indium tin oxide （ITO）-PET electrodes, and outperforms other Cu NW based organic solar cells previously reported. The PCE of the solar cells based on Cu NW electrodes remained at 90% after 500 cycles of bending, while the PET/ITO solar cells failed after 20 and 200 cycles, with sheet resistance of 35 and 15 Ω/sq, respectively.

Bacterial Metabolism-Initiated Nanocatalytic Tumor Immunotherapy

The low immunogenicity of tumors remains one of the major limitations of cancer immunotherapy.Herein,we report a bacterial metabolisminitiated and photothermal-enhanced nanocatalytic therapy strategy to completely eradicate primary tumor by triggering highly effective antitumor immune responses.Briefly,a microbiotic nanomedicine,designated as Cu_(2)O@ΔSt,has been constructed by conjugating PEGylated Cu_(2)O nanoparticles on the surface of an engineered Salmonella typhimurium strain(ΔSt).Owing to the natural hypoxia tropism ofΔSt,Cu_(2)O@ΔSt could selectively colonize hypoxic solid tumors,thus minimizing the adverse effects of the bacteria on normal tis-sues.Upon bacterial metabolism within the tumor,Cu_(2)O@ΔSt generates H_(2)S gas and other acidic substances in the tumor microenvironment(TME),which will in situ trigger the sulfidation of Cu_(2)O to form CuS facilitating tumor-specific photothermal therapy(PTT)under local NIR laser irradiation on the one hand.Meanwhile,the dissolved Cu+ions from Cu_(2)O into the acidified TME enables the nanocatalytic tumor therapy by catalyzing the Fenton-like reaction of decom-posing endogenous H_(2)O_(2) into cytotoxic hydroxyl radicals(·OH)on the other hand.Such a bacterial metabolism-triggered PTT-enhanced nanocatalytic treatment could effectively destroy tumor cells and induce a massive release of tumor antigens and damage-associated molecular patterns,thereby sensitizing tumors to checkpoint blockade(ICB)therapy.The combined nanocatalytic and ICB therapy results in the much-inhibited growth of distant and metastatic tumors,and more importantly,induces a powerful immunological memory effect after the primary tumor ablation.

Nanoscale Thermal Response in ZnO Varistors by Atomic Force Microscopy

We report the application of customer-built scanning thermal microscopy （SThM） based on a commercial atomic force microscope to investigate local thermal inhomogeneity of ZnO varistors. The so-called 3ω method, generally used for measuring macroscale thermal conductivity, is set up and integrated with an atomic force microscope to probe the nanoseale thermal property. Remarkably, thermal contrasts of ZnO varistors are firstly imaged by the SThM, indicating the uniform distribution of spinel phases at triple points. The frequency-dependent thermal signal of ZnO varistors is also studied to present quantitative evaluation of local thermal conductivity of the sample.

Influence of average radii of RE3+ ions on phase structures and thermal expansion coefficients of high-entropy pyrosilicates

High-entropy pyrosilicate element selection is relatively blind, and the thermal expansion coefficient (CTE) of traditional β-type pyrosilicate is not adjustable, making it difficult to meet the requirements of various types of ceramic matrix composites (CMCs). The following study aimed to develop a universal rule for high-entropy pyrosilicate element selection and to achieve directional control of the thermal expansion coefficient of high-entropy pyrosilicate. The current study investigates a high-entropy design method for obtaining pyrosilicates with stable β-phase and γ-phase by introducing various rare-earth (RE) cations. The solid-phase method was used to create 12 different types of high-entropy pyrosilicates with 4–6 components. The high-entropy pyrosilicates gradually transformed from β-phase to γ-phase with an increase in the average radius of RE^(3+) ions ( r¯(RE^(3+))). The nine pyrosilicates with a small r¯(RE^(3+)) preserve β-phase or γ-phase stability at room temperature to the maximum of 1400 ℃. The intrinsic relationship between the thermal expansion coefficient, phase structure, and RE–O bond length has also been found. This study provides the theoretical background for designing high-entropy pyrosilicates from the perspective of r¯(RE^(3+)). The theoretical guidance makes it easier to synthesize high-entropy pyrosilicates with stable β-phase or γ-phase for the use in environmental barrier coatings (EBCs). The thermal expansion coefficient of γ-type high-entropy pyrosilicate can be altered through component design to match various types of CMCs.

Elevating the comprehensive thermal properties of rare-earth cerates through high-entropy design

In the rapidly evolving aerospace sector,the quest for sophisticated thermal barrier coating(TBC)materials has intensified.These materials are primarily sought for their superior comprehensive thermal characteristics,which include a low thermal conductivity coupled with a high coefficient of thermal expansion(CTE)that synergizes with the substrate.In our study,we adopt a solid-state method to synthesize a series of high-entropy rare-earth cerates:La_(2)Ce_(2)O_(7)(1RC),(La_(1/2)Nd_(1/2))2Ce_(2)O_(7)(2RC),(La_(1/3)Nd_(1/3)Sm_(1/3))_(2)Ce_(2)O_(7)(3RC),(La_(1/4)Nd_(1/4)Sm_(1/4)Eu_(1/4))_(2)Ce_(2)O_(7)(4RC),and(La_(1/5)Nd_(1/5)Sm_(1/5)Eu_(1/5)Gd_(1/5))_(2)Ce_(2)O_(7)(5RC),all sintered at 1,600℃ for 10 h.We thoroughly examine their phase structure,morphology,elemental distribution,and thermal properties.Our in-depth analysis of the phonon scattering mechanisms reveals that 4RC and 5RC exhibit exceptional thermal properties:high CTEs of 13.00×10^(−6) K^(−1) and 12.77×10^(−6) K^(−1) at 1,400℃,and low thermal conductivities of 1.55 W/(m·K)and 1.68 W/(m·K)at 1,000℃,respectively.Compared to other TBC systems,4RC and 5RC stand out for their excellent thermal characteristics.This study significantly contributes to the development of high-entropy oxides for TBC applications.

Simultaneous Al2O3 Doping and Sulfation in Hierarchically Porous ZrO2 Solid Acids by an One-pot Synthesis for Enhanced Recycling Catalytic Performances

Alumina doping and sulfation in hierarchically porous zirconia solid acids have been achieved simultaneously via one-pot and bi-surfactant-assisted self-assembly process, using aluminum sulfate as both Al and SO^2- sources. The prepared composite solid acids showed much enhanced acidity and recycling catalytic activity for an esterification reaction compared with sulfated zirconia without alumina doping and Al-doped sulfated zirconia without hierarchically porous structure.