查看更多>>摘要：The influence of an electric field on the phase transition parameters and the electrocaloric response in ferrielectric (NH4)2SO4 was studied using a universal multifunctional adiabatic calorimeter. The very low sensitivity of the phase transition temperature to the electric field, dT0/dE ≈ 5·10-3 K/(kV/cm), was shown to be the reason for the low maximum value of the intensive electrocaloric effect, ΔTAD, at E = 11 kV/cm: direct and indirect measurements gave the values of 0.01 K and 0.05 K, respectively. However, the extensive electrocaloric response revealed by an analysis of the entropy–temperature–electric field phase diagram was relatively large, with a value of ΔSECE ≈ ? 19 J/kg K, due to the significant contribution of a jump in the excess entropy to the total value, δS0/ΔS0 ~ 0.37. An additional irreversible increase in temperature under the electric field was associated with the Joule effect and indicated a significant electrical conductivity of ammonium sulphate.
查看更多>>摘要：Multilayer structure is an effective approach for reducing driving voltages or increasing output electric signal for piezoelectric devices. However, it is a challenge to achieve high piezoelectric coefficient at low sintering temperature. In this work, we fabricated Li2CO3 (LC) doped Pb(Ni1/3Nb2/3)-Pb(Zr,Ti)O3 (PNN-PZT) ceramics via solid state reaction method. Piezoelectric coefficient at low quasi-static signal d33 and effective piezoelectric coefficient under high electric field d33* are 692 pC/N, 1114 pm/V for PNN-PZT+0.2 wt% LC sintered at 950 °C, which is comparable to high temperature sintered commercial Pb(Zr,Ti)O3 (PZT) based ceramics. Detailed piezoelectric, ferroelectric, dielectric properties, temperature stability and material structure were investigated. The planar electromechanical coupling factor Kp, relative dielectric constant εr and dielectric loss tan δ at 1 kHz, Curie temperature Tc, coercive electric field Ec are measured to be 0.557, 4280, 0.025, 113 °C, 4.34 kV/cm. It shows great potential for applications in multilayer structured cofired piezoelectric actuators and transducers.
查看更多>>摘要：Compared with single metal modification, bimetal modification shows good gas sensing properties, but it should be further improved in terms of detection limit. In this work, the hexagonal WO3 (h-WO3) nanorods with Pt and Pd co-modification were synthesized via a simple method. The PtPd@h-WO3 sensor has better gas sensitivity and selectivity to H2S gas. The response is 196.188 to 10 ppm H2S at 120 °C, which is 49.47 times that of the original h-WO3 (3.966). And the detection limit of the PtPd@WO3 sensor can reach the ppt level (as low as 506 ppt). The morphology of the composite material is characterized by SEM, TEM and HRTEM. The gas-sensing mechanism is carefully researched through XPS analysis. Compared with the pure h-WO3, the enhanced gas sensitivity of PtPd@h-WO3 sensor is mainly ascribed to the synergistic effect between Pt and Pd.
查看更多>>摘要：Bio-inspired materials have received broad attention for energy-storage systems owing to their special properties and low cost. Here, a cost-effective and general strategy is developed for preparing nanocluster arrays on leaves as three-dimensional free-standing Li-ion battery anodes. As a demonstrating case study, an FeCo2O4 nanocluster array is constructed on lotus leaf, which displays a high areal capacity of 2.4 mAh cm?2 after cycling 100 times, and a stable Coulombic efficiency of 99.9%. After long-term 900 cycles at [sbnd]10 oC, capacity remains 1.15 mAh cm?2. At a high temperature of 45 oC, capacity keeps 1.95 mAh cm?2 after cycling 150 times. A recoverable rate-performance after three-rounds measurements is also achieved, enabling the anode to be potentially used at different conditions. In addition, the preparation approach is successfully used for making many other composites including ZnCo2O4, NiCo2O4, CuCo2O4 nanocluster arrays on lotus leaves, and ZnCo2O4, NiCo2O4, CuCo2O4, FeCo2O4 nanocluster arrays on bamboo leaves, displaying a good applicability.
查看更多>>摘要：To solve the critical issues like high polarization and unstable cycle ability, it is vital to design low-cost, stable and efficient catalytic cathode material for nonaqueous Li-O2 batteries (LOBs). Herein, a hollow urchin-like hollandite Ag2Mn8O16 electrocatalyst is fabricated by one-step hydrothermal method. The mixed bimetallic oxide with diverse valences (Mn3+ and Mn4+) and active oxygen defects provide sufficient active sites, and Ag[sbnd]Mn[sbnd]O bonds accelerate charge transformation. LOBs with the well-designed porous Ag2Mn8O16 cathode show superior electrochemical performances in LOBs, including ultrahigh specific capacity (7912 mAh gc?1 at 100 mA gc?1), good rate performance (5076 mAh gc?1 at 250 mA gc?1, 64.16%) and long-term cycle stability (320 cycles at 100 mA gc?1 within a limited capacity of 250 mAh gc?1 and 133 cycles at 200 mA gc?1 within a limited capacity of 500 mAh gc?1). This work provides a positive effect on designing better catalytic cathode materials for LOBs and push forward the commercialization progress.
查看更多>>摘要：In this study, the mechanical and processing properties of nanoimprinted nickel-cobalt-chromium medium-entropy alloy (NiCoCr MEA) are investigated using molecular dynamics (MD) simulation. The effects of microstructure, loading velocity, the taper angle of mould, and processing temperature are analyzed by loading force, deformation characteristic, crystal evolution, dislocation distribution, displacement vector, and radial distribution function. Based on the results, both stacking faults and twinning structures appear in NiCoCr MEA during the imprinting process. The formation of stacking fault is affected by grain size, and it always propagates in large grains (grain size = 8.5 nm). Besides, the maximum loading force and the residual stress increase with an increase in loading velocity (200 m/s), caused by the shorter relaxation time for the atoms in NiCoCr MEA specimen with higher loading velocity. Moreover, the temperature is found to affect the microstructure, phase transformation, and dislocation evolutions of NiCoCr MEA specimen. Most of the atoms transform into HCP or amorphous phase at a temperature of 900 K during the equilibrium process. The maximum loading force decreases with an increase in temperature, and atoms strongly adhesion on the bottom of the mould at the higher temperature (900 K). By contrast, the taper angle of mould gives little effect to the mechanical characteristics. There is no obvious trend in the deformation behaviors of the specimens with different taper angles.
查看更多>>摘要：Controllable multilevel resistive switching (RS) and neuromorphic characteristics emerges as a promising paradigm to build power-efficient computing hardware for high density data storage memory and artificial intelligence. Nevertheless, the current nonvolatile memory still endures from reliability and variability of the memristors. In this work, Pt/Al2O3/HfO2/HfAlOx/TiN multilayer memristor was prepared by using atomic layer deposition (ALD) to examine the well-regulated multilevel RS and neuromorphic properties. The memristor was found to demonstrate admirable RS properties, including forming-free, low operating voltage (Set/Reset), high switching ratio (>100), multi-level retention time (104 s), and good durability (1000 switching cycles). Furthermore, seven and four resistance states can be accomplished by modulating CC through set-operation and stop-voltage during the reset-operation. By modulating the multi-level resistance state, the electronic synapse can simulate synaptic plasticity, such as potentiation/depression, paired pulse facilitation (PPF) and spike-timing-dependent plasticity (STDP). Results show that a multilayer memristor has potential in the application of multilevel data storage memory and bionic portable electronic devices.
查看更多>>摘要：In this work manganese oxide films were obtained by electrodeposition and their electrochemical and mass transfer processes in aqueous zinc-ion battery electrolyte were studied by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). Cyclic voltammograms and corresponding mass variation curves of manganese oxide during charge-discharge processes were examined simultaneously on Au-coated quartz crystal electrodes. The investigations were conducted in aqueous electrolytes of different composition (2 M ZnSO4 and 2 M ZnSO4 + 0.1 M MnSO4). Monitoring of electrode mass variation during potential cycling provides direct evidence that redox processes in MnO2 electrodes co-occur with intercalation of protons and zinc ions. Combined CV and EQCM studies reveal that electrodeposited films of MnO2 are unstable in 2 M ZnSO4 electrolyte. The repeated potential cycling in Zn-containing electrolytes leads to rapid deterioration of electrode capacity in the few initial cycles due to the Zn2+ insertion into subsurface structures of MnO2 and blocking of electroactivity of MnO2 film on Au substrate. On the other hand, reversible processes of intercalation of protons and zinc ions occur in 2 M ZnSO4 + 0.1 M MnSO4 electrolyte. Two main steps of mass increase during the discharging process, taking place at 1.4 V (vs. Zn/Zn2+) and in the potential range (1.3–1.0) V were demonstrated by EQCM. The first step of mass increase is mainly related to the intercalation of H+ (as H3O+), whereas the second step of mass increase is mainly associated with formation of surface compounds like zinc sulfate hydroxide salts.
查看更多>>摘要：Sodium-ion batteries (SIBs) have been a promising potential alternative for sustainable electrochemical energy-storage devices. Bismuth-based materials can reserve substantial Na ions through alloying reaction and conversion reaction, leading to superior theoretical capacity. However, the alloying reaction is always accompanied by huge volume change during sodiation/desodiation processes. Herein, a flower-like Bi2Se3/Bi2O3 heterostructure is designed to address the structural degeneration problem of Bi-based materials. Diverse Bi2Se3/Bi2O3 heterostructures are produced via a facile hydrothermal reaction and subsequent annealing process, presenting apparently improved rate capability and cycling stability. Such excellent Na ion storage performance attributes to the charge redistribution around heterointerfaces caused by the unmatched band structure of two building blocks. The redistributed charges induce a dissimilar charged space nearby the phase boundaries, which not only enhance the structural integrity via coulombian force but also accelerate the diffusion of Na ions traversing heterointerfaces through electric field force. Meanwhile, the unique surface conducting states of Bi2Se3 can facilitate charge transport effectively. The initial discharge capacity of electrode reached 571 mAh/g at the current density of 0.1 A/g and maintained 310 mAh/g after 100 cycles. This work may provide a new route to enhance the structural stability of the serious volume expansion electrode materials.
查看更多>>摘要：Moderate operating temperatures and inert heat transfer medium are necessary for improving the safety of thermal hydrogen compression applications. In this work, the structural characteristics and hydrogen storage properties of Ti0.85Zr0.17Cr1.7-xMn0.2FexV0.1 (x = 0.7, 0.8, 0.9) and Ti0.82+yZr0.20-yCr0.9Mn0.2Fe0.8V0.1 (y = 0, 0.03, 0.06) alloys for hydrogen compression under moderate thermal conditions of water bath were systematically investigated. The results show that all the alloys have a single C14 Laves phase. With increasing the Fe content in Ti0.85Zr0.17Cr1.7-xMn0.2FexV0.1 (x = 0.7–0.9) or Ti content in Ti0.82+yZr0.20-yCr0.9Mn0.2Fe0.8V0.1 (y = 0–0.06) alloys, the hydrogen plateau pressure is obviously raised, however, the hydrogen storage capacity declines slightly. Flattened hydrogen plateau is also achieved when the Ti content increases. Therein, Ti0.88Zr0.14Cr0.9Mn0.2Fe0.8V0.1 alloy, with achievement of hydrogen compression from 6.13 MPa at 293 K up to 23.73 MPa at 353 K and hydrogen capacity of 1.64 wt%, outperforms the others for the proposed thermal hydrogen compressor.
NSTL
Elsevier