查看更多>>摘要：? 2022 Elsevier B.V.MnO2 has been studied as the catalyst for oxygen reduction reaction (ORR) in neutral due to its considerably good performance and low cost. Although many studies focus on activity enhancement, little attention has been paid to the activity degradation of MnO2. In this study, we first probe the mechanism of ORR activity decay of MnO2 catalyst in neutral. Electrochemical measurements showed the apparent activity degradation of MnO2 in both short-term and long-time stability tests. After chronoamperometry test, surface amorphization was observed on the catalyst, while no significant amorphization occurred for the absence of ORR catalysis. The activity decay and surface amorphization of MnO2 catalyst are due to the disproportionation reaction of Mn3+ ions in neutral. Mn3+ ions involved in ORR catalysis disproportionate to generate soluble Mn2+ ions, resulting in the surface amorphization together with the change of the highly ORR-active Mn3+/Mn4+ redox to the low ORR-active Mn2+/Mn3+ redox. This study clarifies the activity decay mechanism of MnO2 for ORR in neutral media and provides theoretical support for improving and stabilizing the catalytic activity of MnO2 in the future.
查看更多>>摘要：? 2022 Elsevier B.V.Effective grain boundary (GB) reconstruction process has been proposed by introducing Pr-Fe-Al-Ga intergranular additive in the B-lean Nd-La-Ce-Fe-B multi main phase (MMP) magnets. A coercivity of ~2.0 T was yielded in the Nd-Fe-B sintered magnet with 24 wt% Nd substituted by La-Ce. Detailed structural analysis revealed that the RE6Fe13(Ga, Al)1 phase was apparently formed in the triple junction area, triggered by the conducive intergranular composition environment provided by the B-lean composition and the Pr-Fe-Al-Ga addition. Simultaneously, continuous nonferromagnetic GB phases were generated to decouple the intergranular exchange, accompanied by the suppressed fraction of REFe2 and REOx phases. Elemental distribution analysis demonstrated that Pr preferred to enter La/Ce-rich grains to form a Pr-rich shell that enhanced the magnetocrystalline anisotropy field of La/Ce-rich grain surface. Overall, the Pr-rich magnetic hardening shells and the reconstruction GB structure jointly gave rise to the restrained reversion of magnetic domains, thus an extraordinary coercivity was achieved in the Nd-La-Ce-Fe-B magnet. These phenomena may provide a new insight for the development of high-figure-of-merit Nd-La-Ce-Fe-B permanent magnets.
查看更多>>摘要：? 2022 Elsevier B.V.It has been a challenging and urgent task to synthesize high-performance triethylamine (TEA) gas sensors with ppb-level detection. In this paper, Ag-functionalized α-Fe2O3 nanocomposites with internal cavities were synthesized by successfully decorating Ag+ on Fe3+ covered carbonaceous microsphere (CMS) templates followed by a calcination step. The sample Fe-Ag-II had an extremely high response (Ra/Rg = 822), a fast response (2 s), excellent selectivity, and long-term stability for 100 ppm TEA, and a high response to ppb-level TEA gas (Ra/Rg = 9.32–50 ppb) at 200 °C. The effect of relative humidity on TEA gas sensing sensors was investigated, which has rarely been reported before. Gas sensing tests revealed that CMS templates and the noble metal Ag could both improve sensing response while lowering the operating temperature. The mechanism of the enhanced gas sensing properties is discussed in detail. This work provides new strategies for the improvement of α-Fe2O3 microstructure and the development of more practical TEA sensors.
查看更多>>摘要：? 2022 Elsevier B.V.Ag-alloy bonding wire has excellent physical properties and is widely applied in microelectronics, but growing concerns about circuit failure induced by electromigration (EM) have raised doubts about this material. One point of frequent debate is the diffusion mechanism. This study provides a novel perspective by investigating the evolution of the microstructure via electron backscatter diffraction (EBSD) to settle the controversy over the diffusion mechanism of Ag-alloy bonding wire during EM. Particular focuses are the propensity for grain growth, the effects of the coincidence site lattice (CSL) on the grain boundary network, the texture transition, and the influence of thermal energy during EM. A stage-like transition in the dominant diffusion mechanism in different stages of EM is proposed and substantiated from the viewpoint of microstructure evolution.
查看更多>>摘要：? 2022 Elsevier B.V.The effects of superheating and undercooling on the metastable phase separation (MPS) kinetics for glass-fluxed Fe65Cu35 peritectic alloy were investigated by experiments and simulations. MPS occurred in the experimental undercooling range of 175–297 K, and induced the eccentric core-shell macrosegregation (ECSM) structure. It was first demonstrated that the relationship of the phase separation undercooling ΔTPS and the phase separation time tPS with the superheating ΔTH and the undercooling ΔT could be described by curved-surface functions. The increasing ΔTPS was observed under the smaller ΔTH or greater ΔT condition. Both the rising ΔTH and the ΔT contributed to the extension of the tPS, and then resulted in the expansion of Cu-rich zone as well as the microhardness improvement of Fe-rich zone, indicating the more thorough MPS. Numerical simulations showed that the surface segregation, Marangoni convection and Stokes sedimentation mainly pushed the evolution of the ECSM.
查看更多>>摘要：? 2022 Elsevier B.V.AlxCe100?x thin films with a composition range of ~75.0 < x < 99.5 at% (36.5 < x < 97.5 wt%) were synthesized via combinatorial co-sputtering from an Al and an Al50Ce50 target. The crystal structure, phase fraction, film morphology, electrical resistivity, and temperature-dependent coefficients of thermal expansion (CTE) are all correlated to the AlxCe100?x composition. The as-deposited films form a metastable solid-solution, and annealing leads to the formation of the thermodynamically stable two-phase system of Al and the α-Al11Ce3 intermetallic. Temperature dependent x-ray diffraction (XRD) reveals that the two phases expand independently of one another, and the thin film Al temperature-dependent CTE is similar to bulk Al. The thin film Al11Ce3 intermetallic phase has a nearly constant CTE of ~1.5 × 10?5/°C within the temperature range studied (25–550 °C). To confirm the thin film Al11Ce3 results, bulk stoichiometric Al11Ce3 and +/- 1 wt% Ce samples were prepared and the CTE of each was measured with the same conditions. A Rietveld analysis of the bulk data enabled an estimation of the CTE in each of the 3 orthorhombic lattice parameters, which displayed anisotropic behavior. The thin film and bulk CTE measurements were in very good agreement. Estimations of the temperature dependent CTE of the two-phase alloys are made via the Reuss and Voigt models. By demonstrating the efficacy of the approach, more complex multi-component rapid materials discovery of low CTE Al-alloys can be pursued via the combinatorial thin film synthesis and XRD measurement.
查看更多>>摘要：? 2022 Elsevier B.V.As classical BCC structure solid state hydrogen storage materials, vanadium-based solid solution alloys occupied a prominent position in the field of hydrogen storage materials due to their significant advantages such as the ability to absorb and desorb hydrogen with high capacity under moderate conditions. In this paper, RE-containing medium entropy BCC solid solution alloys were designed. The microstructure, phase composition and hydrogen storage properties of the medium entropy alloys were systematically studied. Microstructural analysis showed that nanoscale crystals were found in as-cast medium entropy alloys obtained by arc melting followed by natural cooling inside the furnace. This is different from the vanadium-based alloys that are often regarded as traditional coarse-grained alloys in the past decades. The V47Fe11Ti30Cr10RE2 alloys can be fully activated by one cycle of hydrogen ab/de-sorption after pretreatment. The kinetic test shows that the time required for the as-cast RE-containing medium entropy alloys hydrogen uptake to 90% saturation is less than 100 s at room temperature. The alloys exhibit very excellent hydrogen absorption kinetic properties than reported alloys takes at least about 300 s. This is due to the fact that the present alloys are composed of nanocrystals with numerous interfaces and grain boundaries, and these defects can act as good channels for the diffusion of hydrogen atoms. The V47Fe11Ti30Cr10Y2 alloy exhibits a maximum capacity of 3.41 wt% at 295 K. The thermodynamics of hydrogen ab/de-sorption and the hydrogen desorption under non-isothermal conditions were also studied in detail.
查看更多>>摘要：? 2022 Elsevier B.V.Previous work did not identify occurrence stage and degree of martensitic stabilization in Cu-based shape memory alloys due to lower heating rate. By flash heating into liquid metals, we systematically clarified contribution of static ageing and the ones of dynamic ageing during process of quenching and heating to the martensitic stabilization in directly-quenched CuZnAl alloys. We discovered that the dynamic ageing during the cooling process of quenching could instantaneously stabilize a few already formed martensites totally although it did not stabilize the overwhelming majority of martensites. The dynamic ageing during the process of subsequent slow heating was responsible for the partial and total stabilization of overwhelming majority of martensites. Both the amounts of martensites stabilized totally by the two dynamic ageing positively depended on Ms temperature. The conventional up-quenching into oil or air actually made more martensites stabilized due to the dynamic ageing during the process of slow heating. The increase in As temperature owing to the static ageing also positively depended on the Ms temperature. These dependences cannot be explained by two well-known mechanisms for the martensitic stabilization.
查看更多>>摘要：? 2022 Elsevier B.V.Piezoelectric nanogenerators (PENG), which convert random mechanical energy into electrical energy, have attracted considerable attention due to their application potential in self-powered micro and nano electronics devices, wearable electronics, sensors etc. PENGs based on ZnO nanostructures are particularly important due to their low cost, flexibility and bio-compatibility. Flexible PENGs based on ZnO nanostructures dispersed in Polydimethylsiloxane (PDMS) in ITO/ZnO:PDMS/ITO device configuration were fabricated and characterized for vibration energy harvesting applications. Surfactant free ZnO nanostructures were grown using co-precipitation route and ZnO:PDMS nano-composite films with ZnO content varying in the range of 1.5–7.5 wt% were deposited on ITO/PET substrates for PENG fabrication. The maximum open circuit voltage and short circuit current of ~ 2.5 V and ~ 4 μA respectively were obtained in PENG fabricated with 6 wt% ZnO. The output characteristics were further enhanced to 5 V and 6 μA with flowing oxygen ambient annealing of ZnO nanostructures generating an instantaneous power density of ~9.55 μWcm?2. X-ray photoelectron spectroscopy studies confirmed reduction in oxygen vacancy and enhancement in oxygen interstitial concentrations on oxygen annealing which leads to the suppression of free carrier induced internal screening in ZnO nanostructures. This suppression of internal screening effect is the possible reason for the enhancement in output characteristics of ZnO:PDMS PENG fabricated with oxygen annealed ZnO nanostructures. The electrical energy generated by the ZnO:PDMS PENG was rectified and effectively stored in capacitors and used to power LEDs and LCD display.
查看更多>>摘要：? 2022 Elsevier B.V.Aqueous rechargeable Zn-ion batteries (ARZIB) are promising candidates for next-generation batteries because of their high safety, low cost, and relatively high capacity. In this study, we developed hydrated and potassium-doped manganese dioxide (MO) nanowires mixed with carbon nanotubes (CNT) on a graphene substrate (hydrated KMO-CNT/graphene) for ARZIB. A simple polyol process using poly(ethyl glycol), KMnO4, CNT, and graphene was utilized to fabricate hydrated KMO-CNT/graphene. MnO2 nanowires with diameters of 15–25 nm possess a high specific capacity with a short diffusion path. The intercalated K ions and hydrates in the layered MnO2 nanowires maintained the MO structure during the charge and discharge processes, whereas carbon nanomaterials (CNT and graphene) enhanced the conductivity of the material. Consequently, hydrated KMO-CNT/graphene demonstrated good ARZIB performance. A high capacity of 359.8 mAh g–1 at 0.1 A g–1, and at a high current density of 3.0 A g–1, a capacity of 129 mAh g–1 with 77% retention after 1000 cycles, were achieved.
NSTL
Elsevier