查看更多>>摘要：Bi2O2Se is a potential medium-temperature n-type thermoelectric material owing to its lower lattice thermal conductivity and larger Seebeck coefficient. However, very low electrical conductivity of pristine polycrystalline Bi2O2Se hinders further enhancement of its thermoelectric performance. In this work, the thermoelectric properties of Bi2O2Se were investigated by Ti-doping with the shear exfoliation- restacking process. The results show that both the electron content and mobility can be further improved by Ti-doping with the shear exfoliation-restacking process, thus a higher electrical conductivity can be obtained. (e.g., 368 S cm?1 of Bi1.99Ti0.01O2Se at room temperature) On the other hand, the thermal conductivity of Bi1.99Ti0.01O2Se is suppressed to 0.84 Wm?1 K?1 at 772 K. Finally, the ZT peak of Bi1.99Ti0.01O2Se is raised to 0.56, which is 1.2 times of that of un-doped sample. The results show that the thermoelectric properties of Bi2O2Se can be further optimized by Ti doping with the shear exfoliation-restacking process.
查看更多>>摘要：Phase-change materials are among the leading candidates that satisfy the need for in-memory computing or computational memory. Ge2Sb2Te5 (GST) is the representative material among them, but amorphous resistance drift in GST limits its cyclable stability. Here, we optimize the properties and microstructure of a GST material by introducing a BiSb phase. Results reveal that the amorphous resistance of GST decreases after the addition of BiSb and the drift coefficient can be reduced to 0.004 because of the decreased disorder in the amorphous state. Further analysis of microstructural characteristics reveals that the distribution of the Bi-Sb phase restrains the diffusion of Sb/Te element and suppresses the formation of voids in GST phases. These features stabilize the nanostructures and suppress resistance drift to a certain extent because of the dual-phase coexistence. Moreover, the conduction of GST compounds changes from a p-type to an n-type, originating from n-type BiSb precipitations. Notably, resistance drift can be further decreased through liquid nitrogen treatment, which restricts atomic mobility in small volumes, changes electron binding energy, and improves the stability of amorphous phases during structural relaxation. Decrease in resistance drift originates from the narrowing of the band gap from 0.65 eV for GST to 0.33 eV for (BiSb)5.1(GST)94.9. Thus, our present research shows that doping GST with BiSb is one of the effective means to obtain ultralow resistance shift in phase-change neuron synaptic devices.
查看更多>>摘要：Construction of heterostructure engineered to modulate the electronic structure and enhance conductivity is an effective approach to enhance the performance of materials. The construction of heterostructure electrocatalysts with efficient catalytic activity by combining 2D nanosheet metal organic frameworks (MOFs) with other earth-rich transition metal oxide materials is a compelling study. Herein, a novel (Fe2O3)0.36@Ni-MOF heterostructure nanosheets has been synthesized by a rapid one-pot hydrothermal procedure as an efficient OER catalyst. (Fe2O3)0.36@Ni-MOF exhibited prominent OER property with the overpotential of 230 mV at10 mA cm?2, a small Tafel slope of 66.7 mV dec?1 and ignorable activity decay after 20 h long-term test at 10 mA cm?2. The excellent properties of (Fe2O3)0.36@Ni-MOF nanocomposite could be attribute to the vast amounts of active sites exposed by the nanosheets and ultrasmall size nanoparticles, and the electronic interaction between Fe2O3 and Ni-MOF in the heterostructure. This work presents an attractive tactics for the preparation of heterostructure catalysts with good OER catalytic performance.
查看更多>>摘要：In this research, surface modification of the Ti6Al4V titanium alloy, by calcium phosphate/graphene composite coatings, was considered to improve the bioactivity and biocompatibility of Ti6Al4V for biomedical applications. Synthetic biphasic calcium phosphate (BCP), derived from bovine bone, with 1%wt. Graphene (Gr) and without Gr, was coated by electrophoretic deposition on Ti6Al4V substrates to improve the bioactivity of surface and the corrosion resistance of electrophoretic coating. Different methods were conducted to characterize and compare the chemical and biological properties of BCP and BCP/Gr coatings. Results revealed that the presence of graphene in BCP/Gr composite coatings led to enhanced mechanical and corrosion resistance properties while composite coating remained bioactive and hydrophilic. Moreover, MTT assay and cell attachment results indicated that BCP/Gr coatings improved the MG-63 cell viability, which was approximately 87% for 7 days. The BCP/Gr coating is a novel and proper choice to modify Ti6Al4V surface properties for biomedical applications.
查看更多>>摘要：The combination of magnetic nanoparticles and transition metal oxides has attracted much attention in microwave absorption applications. Herein, the MnO2/Mn3O4@Ni-Co/graphite carbon (GC) nanocubes with porous structure and ultrathin nanosheets was constructed by self-template strategy and in-situ synthesis. The composites not only synergize the magnetic loss of magnetic Ni-Co nanoparticles with the dielectric losses of GC and MnO2/Mn3O4, but also enhance the multiple interface polarization and improve impedance matching. As a result, the MnO2/Mn3O4 @Ni-Co/GC nanocubes present outstanding electromagnetic wave (EMW) absorption performances, in which a RLmin of ?26 dB at 6.4 GHz with a thickness of 4 mm and an effective absorption bandwidth covering from 5.3 GHz to 6.4 GHz are achieved. Meanwhile, the widest effective absorption bandwidth with the value of 3.7 GHz can be achieved at a matching thickness of 2.0 mm. More importantly, this work provides a new strategy for the synthesis of EMW absorbing materials.
查看更多>>摘要：In multicomponent alloys, different precipitates always form in association with one other. Compared with the precipitates that form individually, little attention has been given to the crystallography of coprecipitates. In this study, we reported and interpreted the novel crystallography of the ε'-Mg54Ag17 coprecipitates observed in a Mg-7Sn-1Mn-2Ag-1Zn alloy. Two types of coprecipitates, i.e.,ε'-Mg54Ag17/β-Mg2Sn and ε'-Mg54Ag17/ε'-Mg54Ag17 were both observed. The ε'-Mg54Ag17 phase with the orientation relationship of (0 0 2)ε'//(0 0 0 2)α, [2 0 0]ε'//[1 1 ?2 0]α is present in both coprecipitates. It exhibits the same orientation relationship and interfacial orientations as those phases that formed individually, but is characterized by an opposite facet size order and a new interface between the coprecipitates, resulting in a distinctly different morphology. For both ε'/β and ε'/ε' coprecipitates, the interface between the two precipitates exhibits a much better lattice match than the initial ε'/α interface, indicating preferred heterogeneous nucleation sites for the later-formed precipitates in the alloy.
查看更多>>摘要：A near-equiatomic TiTaNbMoZr refractory high entropy alloy (RHEA) was prepared by vacuum arc melting. It consists of two BCC solid solution phases (predominant and minor phase are named as B-major and B-minor, respectively) at room temperature. Structural stability and thermal expansion were investigated using in-situ synchrotron XRD and dilatometry. B-major phase is observed until 1273 K, whereas B-minor phase is present up to 1173 K. Above 1173 K, the formation of B′ phase is observed. The mean lattice coefficient of thermal expansion (αlm) and the mean dilatometric coefficient of thermal expansion (αdilm) are derived in the range of 323–1173 K and 323–1273 K, respectively. αlm increases linearly in the range of (8.1–8.8)× 10?6 K?1 and the mean αdilm varies from 7.5 × 10?6 K?1 to 10.9 × 10?6 K?1. Dilatometric strain and lattice strain are found to be identical up to 1000 K. However, beyond 1000 K, the dilatometric strain increases considerably in comparison to the lattice strain due to the generation of temperature-induced point defects (vacancies). The present work demonstrates that the TiTaNbMoZr RHEA exhibits structural (phase) stability up to 1173 K and thermal stability up to 1000 K.
查看更多>>摘要：Herein, we demonstrate the reasonable design and preparation of yolk-heteroshell Sn@N-doped C@MoS2 nanospheres as anode materials in sodium-ion battery. Through an effective multi-step strategy, Sn nanoparticles are encapsulated in N-doped C nanocage surrounded by ultra-thin MoS2 nanosheets to form Sn@N-doped C@MoS2 nanospheres. In this novel structure, Sn nanoparticles with high theoretical capacity improve the space utilization inside the heteroshell; the N-doped carbon nanocage as the skeleton not only inhibits the mutual accumulation of Sn and MoS2, but also improves conductivity; the outer MoS2 ultra-thin sheets can consolidate C@MoS2 heteroshell, provide numerous active sites and favor the fast diffusion of Na+/e-. Notably, the combination of carbon nanocage and MoS2 sheets in the yolk-heteroshell structure can effectually buffer the volume expansion of Sn nanoyolks and reinforce C@MoS2 heteroshell while reducing the carbon content. Therefore, the yolk-heteroshell structure plays a crucial role in enhanced reversible capacity and cyclic stability of Sn@N-doped C@MoS2 nanospheres, which activates their sodium storage potential. The yolk-heteroshell Sn@N-doped C@MoS2 nanospheres exhibit high reversible capacity of 488.4 mAh g?1 at 0.1 A g?1 after 300 cycles and long-cycle stability of 350.6 mAh g?1 at 0.5 A g?1 after 500 cycles. Moreover, their full cell delivers a stable reversible discharge capacity of about 80.1 mAh g?1 after 30 cycles at 0.5 C. This work provides a feasible yolk-heteroshell strategy for Sn-based composite nanomaterials.
查看更多>>摘要：The ever-growing need for sophisticated chemical compounds drives progress in the field of catalysis. It is essential to devise new inexpensive catalytic systems to reduce reaction time, increase the yield, and put a smaller burden on the environment. The discovery of nanomaterials has breathed fresh air into this area. Extraordinary surface-to-volume ratio and various quantum effects made these materials a promising alternative to the traditional catalysts. Particularly notable results come from implementing metal species arranged in 1D, which are referred to as nanowires (NWs). In this review, we illustrate their potential to catalyze various chemical transformations in organic chemistry. We demonstrate how NWs facilitate processes such as coupling and reduction. Furthermore, we show how these species can be used in electrochemistry and photo-catalysis. Finally, having described the advances in these areas, we envision the next steps which should be taken to bring this concept to the phase of commercial implementation.
查看更多>>摘要：An in-situ one-step hydrothermal method is used to prepare hybrid CuSe@NiSe nanosheets with vertical orientation and interpenetrating structure on the surface of copper foam (S-CuSe@NiSe). The S-CuSe@NiSe has excellent electrochemical performance and outstanding cycling performance. The specific capacitance of the S-CuSe@NiSe is 1478 F g-1 at a current density of 1 A g-1 and stabilizes at 990 F g-1 at 8 A g-1. The specific capacitance retention of S-CuSe@NiSe is 81.7% after 10,000 cycles. The all-solid-state flexible capacitors prepared with S-CuSe@NiSe as electrode (S-CuSe@NiSe-SFCs) also exhibit excellent flexibility, superior electrochemical performance and cycle stability. Its capacitance reaches 333 F g-1 at a current density of 1 A g-1. Capacitance retention of 79.3% has been obtained after 10,000 charge-discharge cycles at 2 A g-1.
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