β-Mo2C/MoO2 heterostructures for hydrogen evolution reaction: Morphology and catalytic activity regulated by heteroatom doping

Improving the activity of non-noble metallic electrocatalyst for hydrogen evolution reaction (HER) is an important issue for hydrogen energy utilization. In this work, we reported a new strategy for morphology regulation of β-Mo₂C/MoO₂ heterostructure via heteroatom doping to enhance the electrocatalytic HER activity. Electron microscopy observations found that N and S doping resulted in nanosphere and nanorod morphology, respectively. Amongst the S doping catalyst (denoted as S@β-Mo₂C/MoO₂) exhibited remarkably improved electrocatalytic HER activity and stability as compared to the pristine β-Mo₂C/MoO₂ catalyst, whereas the N doping induced significant degradation of catalytic activity and stability. The mechanism investigations reveal that the nanorod morphology of S@β-Mo₂C/MoO₂ endows it lower charge transfer resistance, higher electrochemical active surface area and lower valence state of Mo species, which contributes positively and importantly to its better electrocatalytic HER activity.     

Macrosegregation and thermosolutal convection-induced freckle formation in dendritic mushy zone of directionally solidified Sn-Ni peritectic alloy

Compared with the growing applications of peritectic alloy,none research on the freckle formation during peritectic solidification has been reported before.Observation on the dendritic mushy zone of Sn-36 at.％Ni peritectic alloy during directional solidification at different growth velocities shows that the freckles are formed in two different regions:region Ⅰ before peritectic reaction and region Ⅱ after peritectic reaction.In addition,more freckles can be observed at lower growth velocities.Examination on the experimental results demonstrates that both the temperature gradient zone melting(TGZM)and Gibbs-Thomson(G-T)effects have obvious influences on the morphology of dendritic network during directional solidification.The current theories onKI Rayleigh number Ra characterizing the thermoso-lutal convection of dendritic mushy zone to predict freckle formation through the maximum of Ra can only explain the existence of region Ⅰ while the appearance of region Ⅱ after peritectic reaction cannot be predicted.Thus,a new Rayleigh number RaP is proposed in consideration of evolution of dendritic mushy zone by both effects and peritectic reaction.Theoretical prediction of RaP also shows a maximum after peritectic reaction in addition to that before peritectic reaction,thus,agreeing well with the freckle formation in region Ⅱ.In addition,more severe thermosolutal convection can be predicted by the new Rayleigh number RaP at lower growth velocities,which further demonstrates the reliability of RaP in describing the dependence of freckle formation on growth velocity.     

Effect of ZIF-67 derivative Co3O4 on Li-rich Mn-based cathode material Li1.2Mn0.54Ni0.13Co0.13O2

The zeolitic imidazolate frameworks 67 (ZIF-67) derivative Co₃O₄ composite lithium-rich manganese-based layered oxide was successfully synthesized by a simple solid-phase sintering method and systematically studied. The introduction of the derivatives does not excessively induce changes in the transition metal layered oxide structure as tested by XRD, SEM, TEM, and XPS. The electrochemical test and analysis show that the high surface area and porous structure of the ZIF-67 derivative Co₃O₄ can promote the contact efficiency of the electrode and the electrolyte, thereby delaying the structural phase change which caused by the long cycle process and suppressing the voltage attenuation. In particular, a composite ratio of 10:1 samples can most effectively improve the first coulomb efficiency, cycling stability, and structural stability of lithium-rich materials. The discharge specific capacity at 0.1 C is 258.9 mAh/g, and the first coulomb efficiency is 74.93%. Especially, the discharge specific capacity at 0.5 C is 234.1 mAh/g, and the capacity retention rate is 86.28% after 100 cycles.     

Research on the preparation technology of polyaniline nanofiber based on high gravity chemical oxidative polymerization

Polyaniline (PANI) nanofibers with higher yield and homogeneous morphology were successfully prepared in larger scale by multi-step oxidation process with high gravity chemical oxidative polymerization (HGCOP) method in a rotating packed bed (RPB) under a higher initial aniline concentration of 0.5 M. The influence of oxidation times and ammonium peroxydisulfate (APS) dosages on the morphology, yield and conductive property of PANI were investigated, the products were characterized by SEM and UV–vis. Moreover, the anti-corrosion property and water dispersity of the as-prepared PANI nanofibers were also studied. The results showed that two-step oxidation process was an efficient way for mass production of PANI nanofibers by HGCOP, in which the optimum molar ratio of APS/aniline in the first and second oxidation stage was 0.5 and 0.25, respectively. PANI nanofibers with yield of 76.1%, diameters of 50–80 nm and average aspect ratio of 9.7 were obtained under the optimized condition. The PANI nanofibers were highly dispersible in water and exhibited an outstanding anti-corrosion effect, which could be applied to the environment-friendly processing and applications.     

Effect of Deposition Temperature on Dynamics and Mechanism of Deposition for Si-B-C Ceramic from BCl3/SiCH3Cl3/H2 Precursor

The deposition rate, phase, chemical composition and microstructure of deposits were determined from 950 to 1100℃. With increasing temperature, the deposition rate increases, and the morphology changes from smooth to coarse, meanwhile, the concentration of silicon increases while that of boron decreases. The deposition process is controlled by chemical reactions, and the activation energy is 271 kJ/mol. At relatively lower temperature (below 1000℃), the deposition process is dominated by formation of B4C. While at higher temperature (above 1000℃), it is governed by formation of SiC. B4C and SiC disperse uniformly in the Si-B-C co-deposition system and form a dense network structure.     

Polymer electrolyte membranes from fluorinated polyisoprene-block-sulfonated polystyrene: Membrane structure and transport properties

With a view to optimizing morphology and ultimately properties, membranes have been cast from relatively inexpensive block copolymer ionomers of fluorinated polyisoprene-block-sulfonated polystyrene (FISS) with various sulfonation levels, in both the acid form and the cesium neutralized form. The morphology of these membranes was characterized by transmission electron microscopy and ultra-small angle X-ray scattering, as well as water uptake, proton conductivity and methanol permeability within the temperature range from 20 to 60 °C. Random phase separated morphologies were obtained for all samples except the cesium sample with 50 mol% sulfonation. The transport properties increased with increasing degree of sulfonation and temperature for all samples. The acid form samples absorbed more water than the cesium samples with a maximum swelling of 595% recorded at 60 °C for the acid sample having 50 mol% sulfonation. Methanol permeability for the latter sample was more than an order of magnitude less than for Nafion 112 but so was the proton conductivity within the plane of the membrane at 20 °C. Across the plane of the membrane this sample had half the conductivity of Nafion 112 at 60 °C.     

Indian water chestnut flour- method optimization for preparation, its physicochemical, morphological, pasting properties and its potential in cookies preparation

Various pre-treatments were given to water chestnut slices before drying in the process of optimizing method for flour preparation. Treatment of water chestnut slices with 0.1 g/100 g KMS (Potassium metabisulphite) and 0.5 g/100 g citric acid for 30 min before drying exhibited best results in terms color of the flour. The calculated mean particle size of water chestnut flour was 268.20 μm. The scanning electron microscopy revealed that the granules present in water chestnut flour were polyhedral, bearing smooth surface having diameter in the range of 5-20 μm. The water chestnut flour prepared by optimized method exhibited higher peak viscosity (PV) at 2611 cP than the water chestnut flour obtained from market at 1912 cP. The breakdown was too higher at 898 cP for water chestnut flour prepared by optimized method against value of 625 cP for market water chestnut flour. Cookies prepared from water chestnut flour exhibited good acceptance and excellent scope in future to be used as a specialized product in Indian market.     

Growth mechanism of house-of-cards aggregates of alumina platelets containing Na2O–B2O3–SiO2 glass flux

Porous alumina bodies, intended for use as heat-insulating refractory materials, were fabricated by a high-temperature evaporation method and characterized. A series of flux systems was used by adding a third component to Na₂O–B₂O₃ glass in addition to boric acid and sodium carbonate. When SiO₂ was added as the third component, the primary alumina particles grew anisotropically, forming a plate-like shape, and the house-of-cards structure was self-organized. The anisotropic growth of alumina platelets was promoted by the solid solution of Si⁴⁺ ions in the flux on the α-Al₂O₃ surface. Furthermore, the bonding between the alumina platelets was strengthened by the high-SiO₂-concentration flux. Our typical alumina body had a porosity of 71.5%, a compressive strength of 3.7 MPa, a shrinkage rate of 2.6% when reheated at 1700 °C, and a thermal conductivity of 0.24 W m⁻¹•K⁻¹ at 1000 °C. Thus, the present alumina bodies are expected to find application as high-performance heat-insulating refractory materials.     

Evolution of TCP Phase During Long Term Thermal Exposure in Several Re-Containing Single Crystal Superalloys

The application and component designs of single crystal superalloys are restricted by the precipitation of topologically closed packed(TCP) phases,which can deteriorate the microstructural stability of the alloys severely.Limited researches concerning the type and morphology evolution of TCP phases under elevated temperature conditions have been reported previously.In the present work,three Re-containing single crystal alloys were designed to investigate TCP phase evolution via long term isothermal exposure tests at 1120℃ while the effects of Re on the microstructural characteristic and elements segregation were also clarified.The results showed that the addition of Re increased the instability of the alloys and the volume fraction of the TCP phases exceeded 5 vol% when the Re content reached 3 wt%.The increasing Re content had also raised the precipitation temperature of TCP phases but it did not change the type of them after long term aging;all the TCP particles were identified as μ phase in this study.Moreover,the elements segregation became considerably serious as Re addition increased constantly,which brought about various morphologies of the μ phase in the experimental alloys.In particular,the rod-like and needle-like μ phases demonstrated the typical orientation within γ matrix while the blocky μphase was dispersedly distributed in the space.No specific orientation relationship could be observed in the μ phase when the addition of Re exceeded certain threshold value.     

Morphology and photocatalytic activity of TiO2/MXene composites by in-situ solvothermal method

In this work, TiO₂/MXene composites were successfully synthesized through an in-situ solvothermal method, where the morphology of TiO₂ nanoparticles (NPs) was modified by different concentrations of agents. Ti₃C₂T_x with electronic storage characteristics was employed as a co-catalyst to enhance the photocatalytic degradation activity by capturing photogenerated electrons. The experimental results reveal that, with the help of C₃H₈O agents, TiO₂ NPs are uniformly distributed on the surface of Ti₃C₂T_x. The TiO₂/Ti₃C₂T_x-C₃H₈O composite showed the highest photocatalytic activity of 90.5% after 75 min under mercury light irradiation, which is 57.9% higher than that of the pure TiO₂ photocatalyst. The photocatalytic activity is promoted due to the high photoelectron transmission performance of the TiO₂/Ti₃C₂T_x composites.