The dynamic responses of sandwich panels with homogeneous and stepwise graded aluminium foam cores subjected to impact loadings were investigated via experimentation and finite element simulation in ...this paper. The low-velocity impact tests were conducted using a drop-weight impact facility at four different velocities, the results of which were compared in terms of force-displacement response, energy absorption and damage status. It was found that the density gradient of graded foam cores had a marked influence on the deformation and failure behaviour of front facesheets. Moreover, different facesheet materials were experimented with a homogeneous foam core, and the results showed that the impact response of a sandwich panel was dominated by its front facesheet. The front facesheets having same materials deformed and failed in the same manner irrespective of the back facesheet materials. The results of finite element analysis indicated that the critical impact energy required to cause failure to the front facesheet increased with the density of first core layer. Besides, the impact performance of sandwich panels could be improved efficiently by increasing the front-to-back thickness ratio while the total thickness of both facesheets remained the same.
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•The density gradient of graded foam cores markedly influenced the deformation and failure behaviour of front facesheet.•The critical impact energy required to cause failure to the front facesheet increased with the density of first core layer.•The perforation resistance of entire sandwich panels was affected slightly by the core density gradient.•The impact performance of sandwich panels was improved by increasing the thickness ratio of front to back facesheet.
The carbon layers wrapped CoFe alloy (C/CoFe-30-650) exhibits high bifunctional catalysis for both ORR and OER, and the rechargeable ZABs with this catalyst has an excellent stability during 20,000 ...charging-discharging cycles.
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Developing high active and stable bifunctional electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential for the development of rechargeable Zn-air batteries. Herein, a facile strategy to synthesize the porous carbon layers wrapped CoFe alloy (C/CoFe) through the pyrolysis of a homogeneous mixture containing Co, Fe ions and N-doped carbon quantum dots (N-doped CQDs) was reported. The prepared carbon layers with multi-level pore structures provides more active sites and optimizes the homogeneity of the electron and mass transport. In addition, the carbon layers, which is doped by Co/Fe/N atoms, is responsible for high ORR activity, while the CoFe alloy plays a vital role in OER performance. The as-synthesized catalyst exhibits an excellent bifunctionality for electrochemical oxygen reactions, which is comparable to the commercial Pt/C and IrO2 benchmarks. Owing to the carbon layers protects CoFe alloy nanoparticles from the harsh environment, the rechargeable Zn–air battery with the C/CoFe catalyst delivers excellent stability during 20,000 charging-discharging cycles.
Ag-MnOx/C composites were prepared using AgNO3 and KMnO4 as the precursors and Vulcan XC-72 as the support. The physical properties of the Ag-MnOx/C composites were investigated via X-ray diffraction ...(XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The activity and the stability of the series of Ag-MnOx/C composites toward the oxygen reduction reaction (ORR) in alkaline media were investigated through the electrochemical techniques. The results show that the main species MnO2 and Ag2O in the fresh sample convert into Mn3O4 and Ag(0), respectively, after the heat treatment in N2 at 300°C (Ag-MnOx/C-300). The Ag-MnOx/C-300 sample shows the highest activity toward the ORR, with the half-wave potential of the ORR shifting negatively only 0.035V compared to that on the commercial 40wt. % Pt/C (JM). The electron transfer number during the ORR on the Ag-MnOx/C composite increases with the value close to four after the heat treatment at 300°C, which is mainly attributed to the formation of Ag(0), rather than Mn3O4. The heat treatment brings about a better catalytic stability of the composite, and no obviously negative shift takes place for the half-wave potential of the ORR on the Ag-MnOx/C-300 composite after 1000 cycles accelerated aging test. The maximum power density of the zinc-air battery with the Ag-MnOx/C-300 air electrode reaches up to 130 mW cm−2, higher than those based on the Pd/C and Pt/C cathode catalysts, which shows that the Ag-MnOx/C-300 composite is a promising candidate as the catalyst for the air electrode.
ABSTRACTMetallic lattice structures based on triply periodic minimum surfaces (TPMS) have attracted extensive attention for their potential application in lightweight and energy absorption. The ...underlying phenomena, mechanisms and modelling under the crushing responses from quasi-static to shock conditions still remain to be revealed. This work systematically investigates the mechanical behaviour of graded additively Schoen-F-RD (FRD) lattice structures under various loading rates. Under dynamic compression, FRD lattices exhibit the ability to withstand larger densification strains at higher plateau strengths, thus, holding enhanced energy absorption capabilities. At medium strain rates, it is the rate-dependence of lattice base material dominates in the strength enhancement, while, at higher strain rates, the role of inertia effect becomes notable. Furthermore, an empirical formula is introduced to predict the shock stress responses. Finally, constitutive models with strain-rates are proposed for the uniform and graded lattices. These findings can provide excellent guidance on the design of energy-absorbing structures.
A series of Ni modified MnOx/C composites were synthesized by introducing NaBH4 to MnO2/C aqueous suspension containing Ni(NO3)2. The physical properties and the activity of the composites toward the ...oxygen reduction reaction (ORR) were investigated via transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and the electrochemical techniques. The results show that the higher activity of the composites toward the ORR is correlated with the higher content of MnOOH species transformed from Mn(II) on the surface of the composite. The main nickel species in the composites is Ni(OH)2, while Ni(OH)2 shows little activity toward the ORR. However, introducing Ni(OH)2 with proper amount into the MnOx/C improves the distribution of the active material MnOx, which contributes to a surface with more MnOOH. The optimal composite is of the Ni/Mn atomic ratio of 1:2 and the MnOx loading of 28 wt.%. The maximum power density of the zinc–air battery with the optimized Ni modified MnOx/C as the cathode catalyst reaches up to 122 mW cm−2, much higher than the one with the MnOx/C as the air cathode catalyst (89 mW cm−2), and slightly higher than those with the Pd/C and Pt/C as the cathode catalysts.
•The higher MnOOH content leads to a better ORR activity.•Proper Ni(OH)2 loading contributes to the uniform distribution of the MnOx.•The optimal Ni/Mn atomic ratio in the composite is 1:2.•The optimal MnOx(Ni/Mn = 1:2) content in the composite is 28 wt.%.•The Pmax for the Zn–air cell with the Ni–MnOx/C cathode is 122 mW cm−2.
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► The catalysts for syngas methanation were studied in the feed containing H2S. ► Mo–Al/25 catalyst calcined at 600°C had the greatest surface and highest activity. ► The saturated ...monolayer coverage was proved to be closet to 25wt.% MoO3. ► Octahedrally coordinated Mo6+ (O) species was not the active catalytic precursor.
The effects of calcination temperature and MoO3 loading on the syngas methanation performance of MoO3/γ-Al2O3 catalyst prepared by the incipient-wetness impregnation method were studied. Mo–Al/25 catalyst (∼4.04Mo/nm2) calcined at 600°C reached maximum activity with 46.45% CO conversion. All of the experimental results demonstrated that the saturated monolayer coverage of MoO3 over a γ-Al2O3 support was closet to 25wt.% MoO3. It was discovered that tetrahedrally coordinated Mo6+ (T), instead of octahedrally coordinated Mo6+ (O), is the active catalytic precursor in its oxidised state. Additionally, it was also confirmed that the presence of crystalline MoO3 and Al2(MoO4)3 species depended on not only the MoO3 loading but also the calcination temperature.
We report novel few-layered ultra-small MoS2 nanosheets, which significantly enhance kinetic performance and structural stability when employed as the cathode in the aluminum-ion battery (AIB). ...During Al3+ insertion, the few-layered structure weakens the electrostatic repulsion and the small size reduces the mechanical stress. Moreover, the high specific surface area exposes more active sites and increases the contact area between the active material and the electrolyte, shortening the ion transport distance.
► A novel palladium coated titanium foam cathode for magnesium–hydrogen peroxide fuel cell (Mg–H2O2 fuel cell) was prepared by electrodepositing palladium onto titanium foam. ► The electrochemical ...measurements demonstrated that titanium foam exhibits excellent corrosion resistance compared to the cathode substrate studied before. ► The performance and stability of Mg–H2O2 fuel cell thus obtained were improved obviously.
The corrosion resistance of several cathode substrates (titanium foam, nickel foam, and silver coated nickel foam) of magnesium–hydrogen peroxide (Mg–H2O2) fuel cells is studied. Titanium foam is found to be the most corrosion-resistant, i.e., the corrosion current density of titanium foam is six orders of magnitude lower than that of nickel or Ag–Ni. Palladium catalyzed titanium foam as a cathode for the Mg–H2O2 fuel cell is prepared by electrodepositing palladium onto the titanium foam substrate. The corrosion resistance of prepared palladium coated titanium is compared with that of titanium foam, nickel foam, and silver coated nickel foam. The structure, morphology and composition of the Pd/Ti are characterized by SEM, EDS, XRD techniques. The influence of the concentration of hydrogen peroxide, sulfuric acid and operation temperature on the performance of Mg–H2O2 fuel cells with the Pd/Ti cathode is studied systematically. The stability of the Mg–H2O2 fuel cell with the Pd/Ti as the cathode is tested and the result shows that Pd/Ti is a promising cathode material for Mg–H2O2 fuel cells.
This paper reports on an enhanced activity of sulfur-resistant methanation catalyst by introducing sulfur powder instead of toxic H2S in catalyst preparation. Ammonium heptamolybdate (AHM) was a ...suitable precursor for this catalyst preparation based on consideration of economy and activity. The effect of S/AHM weight ratio and sulfidation atmosphere on catalyst methanation performance was studied and the optimum S/AHM ratio was 3. Sulfidation atmosphere affected not only methanation activity but also the structure and morphology of the catalysts. The catalyst treated in inert atmosphere exhibited relatively the highest methanation activity with CO conversion as high as 88.2%, which was approaching the thermodynamic equilibrium value. The catalysts characterization results indicated that the as-prepared catalyst at S/AHM ratio as 3 had relatively higher specific surface area and larger pore volume than those with other S/AHM ratio. The MoS2 particles were poorly crystallized with long and straight multi-layered slabs. For the catalyst treated in nitrogen environment, more weakly-bonded sulfur species existed on the surface and more sulfur vacancies resided on the edge planes of MoS2 particles, which are considered to be the active sites for methanation.
► An alternative to prepare highly active unsupported MoS2 catalysts for CO methanation by introducing sulfur powder instead of H2S in catalyst preparation was proposed. The optimum S/AHM weight ratio of as-prepared catalyst for methanation activity was 3. ► Compared with H2S/H2 environment, sulfidation in nitrogen atmosphere yielded catalyst with more surface weakly-bonded sulfur species, which is favorable for active site formation.
GaAs photocathodes are the primary choice for generating spin-polarized electron beam with high brightness, high polarization, and fast polarization reversal. However, it suffers from short lifetime ...due to the highly reactive nature of the emission surface, resulting in substantial operational difficulties. Activating GaAs with a more robust material, such as Cs2Te, shows comparable polarization to that of Cs–O activation and increases the lifetime due to the robustness of the Cs2Te layer. However, previously reported photocathodes based on Cs–Te activation on GaAs suffer from 10× lower quantum efficiency (QE) compared to that activated with conventional Cs–O activation. Herein, we report activation recipes for GaAs photocathodes using Cs, O2, and Te. For Cs–Te activation, the QE was 6.6% at 532 nm. For Cs–O–Te activation, the QE was 8.8% at 532 nm and 4.5% at 780 nm. The negative electron affinity of the activated GaAs was directly measured and confirmed by low energy electron microscopy. We also report the activation layer chemical states and stoichiometry using in situ micro-spot synchrotron radiation x-ray photoelectron spectroscopy.
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