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Abstract: Insights into the relationship between the crystal planes of metal oxides and the catalytic activity of the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER) are essential for developing efficient renewable energy technologies. Herein, spinel Co3O4 nanomaterials were synthesized controllably with the specified morphologies of nanocubes, nanosheets, and nanoplates with different exposed planes of {100}, {110}, and {111}, respectively. The effects of the crystal planes of Co3O4 on the activity for the OER, ORR, and HER were subsequently investigated in alkaline media. Different electrocatalytic performances are possibly attributed to the abundance ratios of Co3+/Co2+ over the different exposed planes. The surface Co3+ ions exhibit higher activity for the OER and HER, whereas the surface Co2+ ions exhibit better performance for the ORR; moreover, higher electroconductivity enhances the polarization current for ORR and HER except OER. [ABSTRACT FROM AUTHOR]

Abstract: With the increasing demand of energy storage towards increasing the use of renewable energy technologies, electrochemical systems with low cost, high safety levels, and low environmental impact are critically needed. Zinc–air/oxygen batteries, which were always considered to be cheap, are losing their competitive advantages due to poor cyclic performance and energy efficiency. Herein, an effective strategy for oxygen recycling, which reduces the cost of oxygen to as low as ¢ 0.2 kWh−1 per cycle, is reported. With the use of oxygen, the performance of zinc–oxygen batteries is largely increased, with a maximum power density of 290 mW cm−2, stable cycling for more than 1500 cycles, an average energy density of 60 %, and elimination of carbonates. A 1 kW/1 kWh zinc–oxygen battery system is also integrated and exhibits a satisfactory energy efficiency of 58 % and a high working power density of 75 mW cm−2. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: A series of carbon fiber felt/PTFE based gas diffusion layers (GDL) for Mg-air fuel cells were prepared by a simple method of immersing carbon fiber felt in PTFE suspension. Critical properties of the as-prepared GDL, including the surface morphology, electronic resistivity, porosity and gas permeability, have been characterized to investigate the effect of PTFE suspension concentration and PTFE content on the properties of the GDL. The micrographs indicated that the PTFE was homogenously dispersed on the carbon fiber felts and showed structure with a microporous layer. The as-prepared GDL exhibited good mechanical property, high electronic conductivity, sufficient water repellency and high gas permeability. Compared with the Mg-air fuel cell with a traditional carbon powder based cathode, the performance and the stability of Mg-air fuel cell with the carbon fiber felt based GDL are improved significantly. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Metal foams are commonly used to withstand impact loading from different directions in real life applications attributable to their superior performance of energy absorption to weight. It has been of special interest to explore the complex yield/failure behavior of metal foams under dynamic impact recently. However, existing studies have mainly focused on crushing behavior under simple quasi-static loading conditions. Hence, this study aims to explore the multiaxial dynamic failure behavior of closed-cell aluminium foams. First, the uniaxial failure behavior of foams with three different apparent densities is experimentally investigated at varying strain rates (10−3-150 s−1) through quasi-static compression and drop weight tests, respectively. It is found that the initial failure strength exhibits evident strain-rate dependency. An empirical relation is established to associate the initial failure strength with relative density and nominal strain rate. Second, the multi-axial failure behavior is characterized based upon the developed microscopic computed tomography (micro-CT) image foam models. It is revealed that at low and medium strain rates, the hardening of the uniaxial failure strength is rate-dependent on the foam cell-wall base material. Under compression-shear and triaxial compression loadings, the initial failure surface in the von Mises - mean stress plane significantly expands with increasing strain rates. After normalized by the uniaxial failure strength at the corresponding strain rates, the failure surface is almost independent of loading or strain rates. The normalized failure surface can be well depicted by an elliptic or a parabolic function. Moreover, with use of suitable plastic Poisson's ratio, the normalized failure surface could be well characterized by Deshpande and Fleck (D&F) model and Miller model. The modified rate-dependent constitutive models are suggested for foam materials subject to quasi-static and dynamic loadings. Image 1 • Multiaxial properties of closed-cell Al foams are characterized based upon micro-CT based models. • Rate dependence of foam cell-wall leads to strain-rate sensitivity of the initial failure strength. • The normalized failure surface is independent of strain rate. • The modified Miller and D&F models are proposed with consideration of strain-rate effects. [ABSTRACT FROM AUTHOR]

Structural responses, deformation modes, blast resistance and energy absorption of foam core signify some major functional characteristics for design of sandwich panels. This study aimed to address these issues by investigating uniform and graded foam core configurations. First, an experimental study was performed and the testing results of blast-loaded sandwich panels were analyzed. Second, a numerical model was developed and validated by comparing the simulation results with the experimental results in terms of deformation modes and back facesheet deflection. Third, the blast resistance of sandwich panels was comprehensively studied based upon the developed numerical models. Due to the high attenuation ability of the shock induced stress wave, the foam core with descending gradient of layer density across the thickness direction provided the highest blast resistance of all the core configurations considered here and its advantage could be further improved by enlarging the density difference of the core layer. While keeping total facesheet thickness unchanged, a relatively thick back facesheet is beneficial to enhance the blast resistance under relative low blast intensity. Finally, an optimization study was performed to improve the blast resistance of graded core sandwich panels. For the single objective optimization, the maximum back facesheet deflection of the optimum design decreased by 24.58% in comparison with that for the initial baseline design. For the multiobjective optimization, the optimal designs obtained from the Pareto solution can significantly enhance weight efficiency without compromising the resistance. Image 1 • A numerical model of sandwich panel against blast resistance was developed and experimentally validated. • The foam core with descending gradient of layer density across the thickness direction provided the highest blast resistance. • A relatively thick back facesheet is beneficial to enhance the blast resistance under low blast intensity. • Single/multi-objective optimization design is conducted to improve the blast resistance of sandwich panel. [ABSTRACT FROM AUTHOR]

Design and synthesis of a low-cost, high-durable, and conductive membrane are paramount in reducing energy losses for alkaline water electrolysis (AWE), which has emerged as a promising technology for green hydrogen production. In this study, we utilize Mg(OH) 2 particles to fill the pores of a low-cost polypropylene/polyethylene (PP/PE) membrane, thereby reducing gas crossover and enhancing conductivity. This leads to the preparation of a Mg(OH) 2 -PP/PE composite membrane. When equipped in a flow-type AWE electrolyzer, this composite membrane exhibits a voltage of 1.93 V at a current density of 0.5 A cm−2 over a 100 h measurement period, which is superior to the commercial polyphenylene sulfide (PPS) membrane's voltage of 2.69 V. Furthermore, the 5000 h stability test, without any conductivity loss in the membrane, further confirms its high stability. The successful design of this composite membrane provides a new approach for high-performance AWE. Mg(OH) 2 -PP/PE composite membrane reduce the gas crossover and enhance the conductivity. The composite membrane equipped flow-type AWE electrolyzer displays a voltage of 1.93 V at a current density of 0.5 A cm−2 for over 100 h which is better than the commercial PPS membrane with 2.69 V. [Display omitted] • A low-cost Mg(OH) 2 -PP/PE composite membrane was fabricated via a simple chemical deposition method. • The Mg(OH) 2 -PP/PE composite membrane displays low gas-permeability, high conductive and hydrophily. • The Mg(OH) 2 -PP/PE composite membrane exhibits excellent alkali-resistant and mechanical strength after 5000 h test. [ABSTRACT FROM AUTHOR]

Spin polarized photocathodes are key to the future operation of electron accelerators such as the ones at Thomas Jefferson National Accelerator Facility and Brookhaven National Laboratory. Currently, these photocathodes come in short supply due to limited production by molecular beam epitaxy. By developing a process to implement similar structures using metal organic chemical vapor deposition, the availability of these devices can be increased. In this paper, we detail the implementation of recent photocathode advancements via metal organic chemical vapor deposition process and show an improvement in both polarization and quantum efficiency of our devices compared to those fabricated via molecular beam epitaxy, with devices reaching 82% polarization and 2.9% quantum efficiency. [ABSTRACT FROM AUTHOR]

Photocathodes based on GaAs and other III–V semiconductors are capable of producing highly spin-polarized electron beams. GaAs/GaAsP superlattice photocathodes exhibit high spin polarization; however, the quantum efficiency (QE) is limited to 1% or less. To increase the QE, we fabricated a GaAs/GaAsP superlattice photocathode with a Distributed Bragg Reflector (DBR) underneath. This configuration creates a Fabry–Pérot cavity between the DBR and GaAs surface, which enhances the absorption of incident light and, consequently, the QE. These photocathode structures were grown using molecular beam epitaxy and achieved record quantum efficiencies exceeding 15% and electron spin polarization of about 75% when illuminated with near-bandgap photon energies. [ABSTRACT FROM AUTHOR]

The lifetime of GaAs photocathodes in polarized electron guns is limited due to the delicate activation layer. An atomically clean and smooth GaAs surface is needed to deposit a robust activation layer, such as Cs 2 Te , with longer lifetime compared to traditional (Cs,O) activation. A previous experiment with Cs 2 Te activation on GaAs used heat cleaning temperatures around 400 ° C to avoid an increase in surface roughness [Bae et al., Appl. Phys. Lett. 112, 154101 (2018)]. High-temperature heat cleaning around 580 ° C , which results in a relatively contamination-free surface, could be one possible way to improve quantum efficiency. However, one should be cautious about surface roughness degradation during high-temperature heat cleaning. In this paper, we report results of surface roughness measurements on native, heat cleaned, and (Cs,O) activated GaAs photocathodes under vacuum. The results, measured by ultrahigh vacuum scanning tunneling microscopy, show that the surface roughness improves as the heat cleaning temperature is increased, by at least a factor of three for 580 ° C heat cleaning, compared to the native sample. Activation with (Cs,O) is shown to increase surface roughness by a factor of four compared to a 580 ° C heat cleaned sample. This confirms that high-temperature heat cleaning can be useful for depositing good quality robust activation layers on GaAs. We also report chemical analysis for each step of preparation for p-doped GaAs photocathodes using X-ray photoelectron spectroscopy (XPS), angle-resolved XPS, and ultraviolet photoelectron spectroscopy. Our results indicate that the (Cs,O) activation layer forms a sandwich structure consists of Cs and oxygen. We found no formation of any specific compound such as Cs 2 O or Cs 11 O 3. [ABSTRACT FROM AUTHOR]

Studying the electrode activity and stability changes caused by the increasing ion concentration during the alkaline seawater electrolysis is crucial to exploit industrial-level seawater electrolyser. Herein, the concentration of hydroxide ion (OH−), chlorine ion (Cl−), and the other ions in alkaline seawater (OIAS) is investigated to understand the activity and stability for nickel foam (NF) electrodes as both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrodes. As a whole, the activity of HER electrode is mainly dropped with the increasing concentration of OH−, while the OER electrode is enhanced with the increasing concentration of OH− and Cl−. However, the all (OH−, Cl− and OIAS) increasing ion concentrations decrease the HER electrode stability, while the Cl− reduces, the OH− and OIAS enhances the stability of OER electrode. Moreover, the chloride evolution reaction (ClER) in 6 M NaOH with seawater can be ignored even though the concentration of salts in alkaline seawater reach to saturation. • The trends of activity and stability of HER and OER electrode changed with ion concentrations increasing. • The reasons for activity and stability changes with the increasing ion concentration. • The suggestions for alkaline seawater electrolysis operation. [ABSTRACT FROM AUTHOR]