查看更多>>摘要：Nanocrystalline materials are well known for their beneficial mechanical and physical properties. However, it is of utmost importance to stabilize the microstructure at elevated temperatures to broaden the window of application e.g. by pinning grain boundaries through impurities or oxides. CuCo alloys, severe plastically deformed using high-pressure torsion, were used to investigate the evolution of oxides upon annealing. These investigations were performed using electron microscopy, synchrotron high-energy X-ray scattering and atom probe tomography. Monitoring the evolution of oxides by in-situ small angle scattering investigations indicates the growth of primary oxides as well as the formation of another species of oxide at elevated temperatures. Slightly different coarsening can be observed in heat-treated samples, which can be traced back to the influence of different oxide amounts. The initially supersaturated CuCo matrix changes by the decomposition process as well as Co- and Cu-based oxides formation and growth. It has been found that the major number of oxides which are present after annealing, can already be found in the starting materials.
查看更多>>摘要：Rare earth group elements have gained the renewed interest in applications of energy storage and conversion. Apparently, supercapacitive performances of electrodes based on yttrium (Y+3) element are still left uncovered for exploration as energy storage device. In this study, the binder free yttrium hydroxide (Y(OH)3) electrodes have been prepared through easy, economical and industry applicable successive ion layer adsorption and reaction (SILAR) method. The Y(OH)3 has been deposited over the stainless steel (SS) substrate for 10 (Y_10), 20 (Y_20) and 30 (Y_30) SILAR cycles. The prepared electrodes have been characterized by using X‐ray diffraction (XRD), fourier‐transform infrared spectroscopy (FTIR), high resolution scanning electron microscopy (HRSEM) and transmission electron microscopy (TEM). The electrochemical performances of the prepared electrodes have been studied in presence of 1 M Na2SO4 electrolyte. The Y_20 shows the superior electrochemical performance than others. The highest specific capacity of 237 C g?1 has been observed for Y_20 at 1 mA current rate along with good cycle stability. Thus, by observing our results, one can say that the prepared electrode has a great potential in area of energy harvesting, power back up, portable devices, etc.
查看更多>>摘要：Carbon materials were regarded as promising anode materials for sodium-ion batteries (SIBs) due to impressive structural integrity and stability upon cycling. However, the moderate discharge capacity and unsatisfactory rate capability had significantly hindered their practical applications. Herein, we reported a Mo2C/N, S co-doped porous carbon composite, in which the Mo2C nanoparticles were uniformly dispersed in the microstructure of porous carbon, result in providing more reaction interfaces and additional pseudocapacitance. On the other hand, the etching and the N, S doping in porous carbon further reveal more defects and active centers, reducing diffusion pathways and effectively providing buffer space for volume expansion. All above merits remarkably boosted the electrochemical performances. When the as-obtained composites were used as the anode materials for SIBs, which presented a high reversible capacity (600 mAh/g at 0.1 A/g after 500 cycles) and good rate performance (510 mAh/g at 2 A/g after 300 cycles).
查看更多>>摘要：The effect of multicomponent Tb70?xPrxCu10Al10Zn10 (x = 0–30) film diffusion on microstructure and magnetic properties of sintered Nd-Fe-B magnets was investigated in this paper through magnetron sputtering system. The coercivity increased significantly from 11.5 kOe to 17.5 kOe, 18.8 kOe, 19.8 kOe, and 17.8 kOe for the processed samples by Tb40Pr30Cu10Al10Zn10, Tb60Pr10Cu10Al10Zn10, Tb70Cu10Al10Zn10 and Tb, respectively. The remanence and the maximum magnetic energy product of multicomponent film diffused magnets were all higher than those of Tb diffused magnet. Particularly, compared with Tb diffused magnet, the ΔHcj/wt%Tb (the coercivity enhancement per wt% Tb usage) of Tb40Pr30Cu10Al10Zn10, Tb60Pr10Cu10Al10Zn10 and Tb70Cu10Al10Zn10 diffused samples increased by 105%, 63.4% and 57.5%, respectively. It is obviously that the Tb utilization in multicomponent diffusion sources has a higher efficiency in coercivity enhancement. The quantitative analysis of Tb distribution was characterized for comparison. The extra addition of Cu/Al/Zn elements in Tb70Cu10Al10Zn10 diffusion source would enter into the rare earth-rich (RE-rich) grain boundary phases, and an easy diffusion channel was formed to promote the infiltration of Tb element. The results show that improved distribution uniformity of the Tb-rich shell, deeper shell-core structure and the increased local grain boundary phases are the key factors for the significant enhancement of coercivity in multicomponent diffusion magnet. In addition, on one hand, the easily combination of Tb and Cu/Al/Zn elements effectively prevented Tb from entering the main phases. On the other hand, the thinner shell-core structure was observed due to the uniform distribution of Tb in Tb70Cu10Al10Zn10 diffused magnet. These two factors jointly lead to the increase of remanence. This work puts forward that using multicomponent alloy as diffusion sources provides a composition diversity and cost-effective way to enhance the magnetic properties of sintered Nd-Fe-B magnets, while reducing the consumption of Tb.
查看更多>>摘要：Ti-V-Nb-Cr alloys have been reported as potential candidates for hydrogen storage applications. Investigating the processes of absorption and desorption is paramount to understand the hydrogen storage properties of these novel alloys and to develop more efficient hydrogen storage materials. In this work, we investigated the hydrogen absorption/desorption reactions of the (TiVNb)85Cr15 BCC multicomponent alloy by laboratory and synchrotron X-ray diffraction, Pair Distribution Function (PDF) analyses, Transmission Electron Microscopy (TEM) and thermo-desorption analyses (TDS). Hydrogen absorption behavior was studied by pressure-composition-isotherm (PCI) at room temperature, which demonstrated levels of absorption around 2 H/M (H/M = hydrogen-to-metal ratio) with low equilibrium pressure. The results showed a multi-step hydrogenation process: alloy ? BCC solid solution ? BCC intermediate hydride ? FCC dihydride. PDF analyses showed that the partially hydrogenated alloy at different levels of H/M and the fully hydrogenated alloy can be reasonably described by models with phases presenting random atomic distribution in the metal crystallographic sites. Moreover, the partially hydrogenated sample prior to the complete formation of the intermediate hydride showed evidence of two co-existing BCC phases.
查看更多>>摘要：Groping for catalysts with outstanding activity and durability is of significance toward oxygen evolution reaction (OER). We have fabricated a self-supporting electrode by decorating CeO2 on Co-Mn-S nanosheets grown on nickel foam (CeO2/Co-Mn-S/NF). As-prepared material shows preeminent electrocatalytic activity toward OER, with minor overpotential (239 mV at 10 mA cm?2) and Tafel slope (93.2 mV dec?1). Particularly, CeO2/Co-Mn-S/NF exhibits small charge transfer resistance, revealing quick Faradic process and favorable OER kinetics. Moreover, during uninterrupted water oxidation process, CeO2/Co-Mn-S/NF remains long-term stability. The strategy of decorating CeO2 on Co-Mn-S nanosheets opens a new perspective for designing highly efficient electrocatalysts toward OER.
查看更多>>摘要：Morphology of secondary grain boundary α phase (αGB) has great influence on grain boundary Widmanst?tten α phase (αWGB) cluster and further fracture toughness and ductility of the titanium alloys. In this paper, the bifurcation behavior and morphology of secondary αGB in TC18 titanium alloy were investigated through high and low temperature two-step heat treat experiment (910 °C/30 min→800 °C/45 min/WQ) combined with a three-dimensional reconstruction experiment. It was found that αGB showed flat, equiaxed, zig-zag morphologies, and αGB bifurcated to reduce the energy of the system and maintained the stability of structure by interfacial instability nucleation. There exist two types of bifurcation behaviors, bi-direction bifurcation and tri-direction one. The significant difference between them is nucleation positions, β/β grain boundary or the triple junction (TJ) of β grain boundary. The bifurcation behavior of α phase at TJ is related to its original morphology. Bi-direction bifurcation occurs mostly in the flat αGB, but is not observed in the zig-zag αGB. The present results provide new information on αGB of TC18 titanium alloy.
查看更多>>摘要：Suffering from a relatively low energy density, carbon-based supercapacitors are restricted in the practical applications for green energy. However, heteroatom-doped hierarchically porous carbon materials (HPCs) can deliver prominent electrochemical performance as an electrode material. Herein, we report a simple two-step method for the synthesis of oxide-doped HPC with an ultra-high specific surface area of 3043.3 m2 g?1. In a three-electrode system, the specific capacitance of the oxide-doped HPC is as high as 375 F g?1 at 1 A g?1. Also, an aqueous symmetric supercapacitor (AS) assembled with the oxide-doped HPC achieves a high specific capacitance of 353 F g?1 at 1 A g?1 and excellent rate performance of 84.9% capacitance retention with current density up to10 A g?1. Most importantly, the energy density of the AS in the 3 M KOH solution can reach up to 17.7 Wh kg?1 at a power density of 600 W kg?1. In 1 M Na2SO4 solution, the specific capacitance of the AS shows no decay after 5000 cycles at 5 A g?1. These results reveal that the as-prepared oxide-doped HPC has great potential as an electrode material to realize remarkable electrochemical performance in supercapacitors.
查看更多>>摘要：The poor cycle stability and low volumetric energy density of lithium-sulfur (Li-S) batteries caused by the shuttle effect of polysulfides and low density of sulfur cathode restrict their practical application. Composite materials of ultra-light carbon and polar metal compounds are usually used as sulfur host materials, but they can lead to the low volumetric energy density of resulting Li-S batteries. Herein a lightweight 3D free-standing aerogel consisting of N-doped reduced graphene oxide modified by Co4N nanoparticles (3DNG-Co4N) are designed and synthesized, making full use of the superior electrical conductivity of the 3D network structure and the excellent adsorption capacity and catalytic activity of Co4N nanoparticles on polysulfides. The 3DNG-Co4N/S cathodes with ultrahigh sulfur loading of 24.0 mg cm?2 pressed at 20 MPa achieves a high areal capacity of 21.8 mAh cm?2 and volumetric energy density of 2678.1 Wh L?1 at 2.0 mA cm?2 with an electrolyte/sulfur ratio as low as 3.3 μL mg?1, which are among the best results in Li-S batteries. This work provides an effective strategy to design high volumetric energy density Li-S batteries with high sulfur loading.
查看更多>>摘要：The crystal structure with different cationic sites and the superiority of allowing doping make TTB (tetragonal tungsten bronze) structures very interesting in terms of exhibiting different physical properties. The new spectroscopic and structural results of MTa2O6:Eu3+ (M = Sr, Ba, Pb) phosphors were presented in the study. The incorporation of europium activator into the different cationic (Sr, Ba, Pb) tunnel structures of TTB crystal with TaO6 octahedral exhibited interesting structural and optical properties. The relationship between coordination number and CTB showed that the highly coordinated A and B sites of TTB crystal caused the CTB to shift to low energy or over 300 nm. The spectral properties of TTB-MTa2O6:Eu3+ (M = Sr, Ba, Pb) phosphors were compared by determining the Judd-Ofelt (JO) intensity parameters from PL emission spectrum. The (decreasing trend of the Ω2 parameter and asymmetry ratio is SrTa2O6:Eu3+>BaTa2O6:Eu3+>PbTa2O6:Eu3+, and the Eu–O bonds of PbTa2O6:Eu3+ compared to other matrices indicated a more ionic character and a relatively high symmetry environment around Eu3+. The deviation of the experimental (βexp) and Judd-Ofelt (βcal) branching ratios for transition 5D0→7F2 are well below 10%, indicating good consistency. All the 5D0 decay profiles of the phosphors are exponential, and slightly reductions occurred in the luminescence lifetimes for SrTa2O6:Eu3+ and BaTa2O6:Eu3+. XRD results of Eu3+ doped SrTa2O6 series of the high-temperature TTB polymorph reported in this study confirmed the single-phase up to 10 mol%. SEM examinations revealed the change of size and shape of SrTa2O6 samples depending on Eu3+ concentration.
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