Search

The polarized electron source is a critical component in accelerator facilities such as the electron–ion collider, which requires a polarized electron gun with higher voltage and higher bunch charge than existing sources. One challenge we faced was the surface charge limit of the distributed Bragg reflector GaAs/GaAsP superlattice (DBR-SL-GaAs) photocathode. We suppressed this effect by optimizing the surface doping and heat cleaning procedures. We achieved up to 11.6 nC bunch charge of polarized electron beam. In this report, we discuss the performance of tests of a DBR-SL-GaAs photocathode in the high voltage direct current gun. Possible reasons for the observed peak quantum efficiency wavelength shift are analyzed, and we addressed it by using a wavelength tunable laser. In addition, the impact of the DBR layer and laser on the lifetime is investigated in this paper. The optimal DBR-SL-GaAs operating zone has been proposed, which gave us a long lifetime and high polarization at 30 μA operation. The success of this polarized gun will be key to the future of the nuclear sciences. [ABSTRACT FROM AUTHOR]

A Monte Carlo model was developed to simulate electron transport and emission from thin GaAs photocathodes with different active layer thicknesses and dopant concentrations. The simulation accurately predicts expected behavior, namely, quantum efficiency (QE) is enhanced for thicker GaAs photocathodes and for higher dopant concentrations. More significantly, the simulation predicts that electrons excited to the conduction band of the GaAs can be reflected by the band bending regions of the AlGaAs barrier layer, which contributes to enhance QE. The simulation also predicts that electrons in the conduction band suffer more scattering for thicker GaAs photocathodes and for higher dopant concentration, leading to longer emission response time. This Monte Carlo model will improve our understanding and predicting of the performance of more complicated GaAs-based heterojunction structures composed of multiple thin layers. [ABSTRACT FROM AUTHOR]

The simulation and optimization of an electron injector that operates a high-intensity polarized electron beam are presented. The electron injector would provide a single-bunch electron beam at a repetition rate of 1 Hz with a bunch charge of 10 nC, kinetic energy of 400 MeV and an electron spin polarization of 85 %. A direct current (DC) high-voltage photogun was employed to produce the 10 nC polarized electron beam with a kinetic energy of 350 keV, beam diameter of 1.44 cm (Gaussian distribution with σ of 0.36 cm) and full bunch length of 1.3 ns (Gaussian distribution with σ of 0.325 ns). The beam was compressed to 6 ps of RMS bunch length using one 114.24 MHz standing-wave sub-harmonic buncher, two 571.2 MHz standing-wave sub-harmonic bunchers and one 2.856 GHz traveling-wave buncher. The beam was accelerated finally to 400 MeV via eight 2.856 GHz traveling-wave Linacs. We performed the beam simulation, and the simulated results showed that the optimized RMS bunch length was 4.65 ps, RMS relative energy spread was 0.48 % and normalized RMS transverse emittance was 3 0. 1 3 m m ⋅ m r a d at a beam energy of 400 MeV. [ABSTRACT FROM AUTHOR]

• Manufacturing technologies of metallic cellular materials (MCMs) are outlined. • Micromechanical identification approaches of MCMs are compared. • Mesoscale models to define the structural configurations of MCMs are discussed. • Macroscopic constitutive behaviors of MCMs are summarized and commented. • Mechanical responses and applications of MCMs and structures are reviewed. Lightweight metallic cellular materials (MCMs) have been seen in numerous engineering applications to date, primarily due to their excellent mechanical characteristics such as low weight, high specific stiffness/strength, good energy absorption capacity as well as other multifunctional properties. Moving forwards, MCMs configurations and structures are typically built up by sophisticated interconnected topology comprising of various solid struts or plates. Practical applications of cellular materials mainly exploit their homogenized effective properties, which are strongly relied on the mesoscopic and/or microscopic characteristics of unit-cell materials and structures, stimulating significant research interest in this area. In this present review, typical manufacturing technologies and design optimization strategies are briefly outlined for MCMs at first. Then, the advances in the micro‑meso-macro (MMM) multiscale mechanical properties are reviewed. A range of inverse identification approaches are compared for characterizing mechanical properties of MCMs at microscale. Some mesoscale models that are utilized to define the structural configurations of MCMs are discussed. Characterization of macroscale multiaxial mechanical behaviors of MCMs are reviewed in detail, which involves experimental tests, numerical modeling, inverse calculation, and material constitutive models available in commercial codes. Finally, the mechanical responses of representative MCMs-based structures as well as the advanced engineering applications are outlined. This systematic review is expected to highlight the state-of-the-art and shed some light on the prospects for researchers and engineers to realize desirable multiscale mechanical properties and expand more practical applications of MCMs. [Display omitted] [ABSTRACT FROM AUTHOR]

Here, we report a demonstration of electron beam generation in a superconducting radio frequency (SRF) Teraelectronvolt Energy Superconducting Linear Accelerator 1.3 GHz gun equipped with a field emission cathode and operated at 2 K. The cathode is a submicrometer film of nitrogen-incorporated ultrananocrystalline diamond [(N)UNCD] deposited atop a Nb RRR300 cathode plug that is 4 mm in diameter. Measurements of the output current showed that it increased exponentially as a function of the gun gradient. Our results demonstrate a feasible path toward simplified fully cryogenic SRF injector technology. At a maximal gradient of 0.9 MV/m, a current density of 22 μA/cm2 was obtained [calculated as a 2.75 μA current over the total cathode surface area of π(2 mm)2]. One important finding is that the electron emitter made of (N)UNCD, a material long been known as a highly efficient field emission material, demonstrated a record low turn-on gradient of 0.6 MV/m. A hypothesis explaining this behavior is proposed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract 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. Graphical abstract Unlabelled Image Highlights • 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. [ABSTRACT FROM AUTHOR]

• Multiaxial properties of additively manufactured Kelvin foams are characterized. • Initial yield surface can be well fitted using a parabolic or an elliptic function. • The normalized initial yield surface is still relied on the strut diameter. • Effects of SLM defects and EPS foam filler on the yield behaviors are studied. Additively manufactured lattice structures (AMLS) exhibit substantially more freedom in design compared with traditional cellular materials such as honeycombs and stochastic foams. Prior to extensive applications, multiaxial mechanical behaviors of AMLS need to be thoroughly understood. In this study, open-cell Kelvin lattice structures (named as Kelvin foams) are fabricated through the selective laser melting (SLM) process using 316L stainless steel powder. Multi-cell numerical models are developed and validated against the uniaxial compressive results and then adopted to simulate virtual triaxial experiments. An energy dissipation point is adopted to define onset of yielding. Multiaxial yield surface of Kelvin foams is characterized in the von Mises and mean stress plane, which can be well fitted in terms of an elliptical or a parabolic yield function. The normalized yield surface using uniaxial yield strength is still relied on the strut diameter. It is found that the yield surface is gradually shrunk with increasing strut-diameter dimensional tolerance induced by the SLM process, which becomes more pronounced when its stress state is close to a hydrostatic compression. The yield surface is found to expand when the expanded polystyrene (EPS) foam is used as a filler material, but the influence of foam filler becomes weaker when gradually experiencing hydrostatic compression. [ABSTRACT FROM AUTHOR]

• High-temperature and dynamic compressive responses of Al foams are studied. • Initial failure surface of Al foams is identified under high temperature conditions. • A theoretical constitutive model is proposed involving strain-rate effects. • The strain-rate dependent macro-mechanics models are numerically evaluated. Metallic foams exhibit great application prospects in some extreme working conditions such as high temperatures and/or high-velocity impact environments, but predominantly, their mechanical behavior has remained to be fully understood to date. In this study the uniaxial and biaxial tests are conducted on closed-cell aluminum foams at elevated temperatures. It is indicated that both drop stress and initial failure strength exhibit approximately linear relationship with the applied temperature, while the densification strain keeps almost at a constant value. The higher foam density or lower applied temperature, the larger the initial failure surface characterized in the von Mises - mean stress plane. However, the normalized failure surfaces nearly do not depend on foam density or temperature, and can be well fitted in terms of elliptical or parabolic function. Dynamic compressive tests under constant strain-rates reveal that the compressive strength is correlated to strain-rate positively, but the densification strain negatively. A novel rate-dependent constitutive model is proposed to describe the compressive constitutive behavior of Al foams. Finally, the crushable foam model with the tabular input of yield ratio approach can produce satisfactory numerical predictions compared to dynamic experimental results. This study provides new insights into the intrinsic mechanical properties of metallic foams under some extreme conditions. [Display omitted] [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]

As one of widely-used multi-functional materials, metallic foams are often subjected to multiaxial stress states in practical applications; in which the yield behaviors under different stress states need to be better characterized. However, it is difficult to conduct multiaxial mechanical tests on foam materials, especially under arbitrarily proportional triaxial loadings. In this study, numerical modeling of the yield properties of aluminum (Al) foam is performed based upon 3D image-based models. Real structural models of the Al foam are reconstructed using microscopic X-ray computed tomography (micro-CT) technique for multiaxial characterization computationally. Numerical simulation reveals that plastic collapse and fracture of cell-walls first occur in a relatively weak zone under prescribed uni/tri-axial loadings, whereas happen in the central section under biaxial loadings. An initial yield criterion is defined based upon energy dissipation. A constant stress proportion coefficient can be obtained under the stress-controlled triaxial proportional loading and its effectiveness is also validated by comparing the stress-strain responses with those under velocity-controlled uniaxial and hydrostatic compressive loading. It is found that the initial yield points of foam specimens can be obtained in different stress states in the von Mises-mean stress space. The normalized yield surface is approximately independent of relative density and can be well fitted to a parabolic or an elliptic function. Comparisons between the numerical yield surface and three typical theoretical yield criteria suggest that the Deshpande and Fleck's criterion provides more precise predictions than Gibson and Miller yield criteria when a proper plastic Poisson's ratio is adopted. Furthermore, it is shown that the early stage yield surface of metallic foams can be evolved in a geometrically self-similar manner. Image 1 • Multiaxial characterization of closed-cell Al foams based upon 3D image-based models. • The normalized initial yield surface is well fitted with a parabolic or an elliptic function. • Deshpande and Fleck's criterion provides more precise prediction. • The early stage of the yield surface of metallic foams is evolved in a geometrically self-similar manner. [ABSTRACT FROM AUTHOR]

• A novel approach for the hardening parameters identification of cell-wall of closed-cell aluminum foam. • The objective function considers both the indentation curve and the pile-up information. • The optimization process combines 2D with 3D numerical simulations to improve the efficiency. • The material properties of cell-wall of aluminum foam are experimentally verified. This study aims to develop an inverse approach to identifying the cell-wall material properties of closed-cell aluminum (Al) foams, which is based upon indentation tests, numerical simulation and optimization technique. Vickers nano-indentation tests are conducted on the cell-wall of foams, and the residual surface deformation is measured by a high definition confocal microscopy. To enhance identification efficiency, a combined 2D with 3D micromechanics modeling strategy is proposed here, in which the load-depth curve and residual imprint (pile-up) of the indentation tests are considered. In this study, the cell-wall material properties such as the yield strength and strain-hardening exponent are identified using this proposed inverse approach, while the Young's modulus is obtained directly for the unloading part of the indentation load-depth curves. The identification results indicate that the proposed inverse procedure can provide a well-posed solution to the cell-wall material properties by introducing the pile-up information. Microscopic computed tomography (μCT) technique is also utilized to reconstruct accurate 3D image-based representative volume element (RVE) model of foam structure, through which the numerical simulation is conducted for uniaxial compression. The identified cell-wall material parameters are validated by comparing the numerical simulation with the experimental data in terms of the deformation/failure modes and quantitative results. It is noted that the cell-wall of aluminum foams that are commonly made of melt foaming processes exhibits a quite different stress-strain relation when compared with the raw material of cell-wall. This study is expected to provide an effective approach for identifying the material properties that may be not easily determined through conventional testing methods. Image, graphical abstract [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]

• Experimental studies on aluminum foam-core sandwiches with three different facesheet materials namely aluminum alloy, steel, and carbon fiber reinforced plastic (CFRP) subjected to blast impulse. • Analysis of deformation/failure modes of the whole sandwich panels as well as the front facesheet, foam core, and back facesheet. • Influence of facesheet materials and configuration on the blast resistance of sandwich panels. • Effect of core density gradients on the blast resistance as per the permanent deflections of back facesheets. Sandwich panels with an energy-absorbing core material have exhibited great potential in lightweight structures for blast protection. In this study, the deformation/failure modes of sandwich panels against blast impulse were investigated experimentally. The blast tests were conducted on the aluminum foam-core sandwich panels with different facesheet materials, namely aluminum alloy, steel, and carbon fiber reinforced plastics (CFRP); and the cores involve uniform foam and graded foam. The deformation modes of the whole sandwich panels as well as the front facesheet, foam core, and back facesheet were analyzed systematically. It is shown that the deformation patterns are fairly sensitive to the impulse intensity, facesheet material, and foam core gradient. Based upon the measurements, the back facesheet deflection increases linearly with the impulse, apart from the petal-tearing failure of front facesheet. When considering the specific impulse and the same metallic back facesheets, the blast resistance of the sandwich specimen with CFRP front facesheet is superior to these of the metallic front facesheet specimens. Interestingly, the sandwich panels with the aluminum front and steel back facesheet perform better in blast resistance than those with the steel front and aluminum back facesheet. The blast resistance of sandwich panels with a positive gradient of core density (i.e. core density linearly decreased along the blast direction) is superior to those with a negative gradient of core density; and the performance increases with increasing density difference. Compared with the uniform core, the positively-graded foam core with a larger density difference exhibits a stronger blast resistance, while those with a smaller density difference present a weaker blast resistance. The study is expected to provide some fundamental data and design guide for a more efficient sandwich structure with lighter weight and higher capacity of blast protection. Image, graphical abstract [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]

Al is one of the principal alloying elements for Mg anodes. In this study, a series of Mg–Al alloys has been evaluated as anode materials for optimizing the Al addition amount in Mg anodes with the intention of improving the discharge performance in aqueous batteries. The effect of Al content on the discharge potential and corrosion resistance of the Mg anode has been investigated through microstructure characterization, electrochemical measurements in a half‐cell, discharge morphology analysis, and Mg–water battery tests. The results show that the Mg–1Al alloy possesses a larger corrosion resistance during discharge, with significant increase of the anode utilization efficiency at 1 and 5 mA/cm2 compared with pure Mg. However, a further increase of Al content does not continuously improve the discharge performance of the Mg anode with the decline of utilization efficiency due to the influence of the precipitated phase. This study contributes to a better understanding about the effect of Al on anodic dissolution and corrosion kinetics of the Mg anode. [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]

An issue associated with aluminum-based batteries is the drastic parasitic corrosion of aluminum anode, which significantly restricts the utilization of aluminum. An effective approach is to add inhibitors in electrolytes to reduce the anode corrosion rate. In this work, Na 2 SnO 3 and casein are proposed to act as a hybrid inhibitor in alkaline aluminum-air fuel cell. It is demonstrated that 0.05 M Na 2 SnO 3 and 0.6 g L −1 casein offers the strongest corrosion protection, reducing the corrosion rate by approximately one order of magnitude. The corrosion inhibition is mainly attributed to the inhibition of cathodic reaction process. In addition, the analysis on the morphology and composition of the aluminum surface suggests that casein can greatly promote the deposition of tin to form a uniform and stable layer on the aluminum surface, due to the strong adsorption of polar functional groups in casein. Furthermore, the use of the hybrid inhibitor in aluminum-air fuel cell contributes to an increase of discharge capacity by 89.3%. [ABSTRACT FROM AUTHOR]

In this work, a high-specific-energy magnesium/water battery (Mg/H 2 O battery) combining Mg oxidation with hydrogen evolution reaction (HER) is developed for full-depth ocean application. With the optimized platinum loading associated with moderate Ni(OH) 2 on nickel foam, the performance can be increased obviously. Coupled with AZ91 Mg alloy anode, the specific energy of Mg/H 2 O battery reaches a dramatic value of 1003 W h kg −1 . Moreover, ultrahigh pressure of 1100 bar in the deep-sea simulated condition brings negligible effects on the performance of battery and electrodes. The influence of low temperature can be reduced to an acceptable level under the application at low discharge current density. Stable discharge of the battery for 100 days is also obtained. This work provides a new idea to supply power source with high specific energy, excellent environment adaptability, good safety and low cost for underwater application. [ABSTRACT FROM AUTHOR]

Zinc/air batteries have received extensive attention due to their low cost, high safety, and high energy density. However, as the zinc/air battery is operated in the practical environment, water exchange between the battery and the environment occurs and affects the specific capacity and service life of the battery. In this paper, high relative‐humidity water‐vapor‐resistant membrane is prepared based on water‐absorbent polyacrylic acid. Using this membrane, water exchange is effectively reduced due to the decreased humidity gradient through gas diffusion electrode. When the thickness of the PAA wet film is 150 μm, the water vapor transmission rate (WVTR) reduced to 51 % of the blank. The excellent discharge performance of zinc/air battery is also achieved with the discharge voltage plateau of 1.10 V and the specific capacity of 612.5 mAh g−1 under the current density of 20 mA cm−2, which is 33.8 % higher than that without PAA membrane. [ABSTRACT FROM AUTHOR]

Summary: Aqueous zinc batteries (AZBs) hold great promise for advancing applications in next‐generation energy storage devices because of their high safety, high energy density, and low cost. However, zinc metal anodes have greatly impeded the application in AZBs due to their poor cycle performance. Short lifespan, which is caused by dendritic growth, deformation, corrosion, and competing hydrogen evolution, is very tricky. Herein, a stable Sn@Cu foam, prepared by plating tin on copper foam, is reported as the substrate of Zn anodes. We evaluate the quality of plating tin layers, which are prepared by using different tin salt solutions, and Na2SnO3 solution is eventually selected. Electrochemical tests show that Sn@Cu foam can not only inherit the merits of Cu foam but also suppress hydrogen evolution reaction and lower the initial heterogeneous nucleation barrier of deposited Zn. Moreover, in situ observation by optical microscope demonstrates that Zn dendrite growth on Sn layer is suppressed during the plating‐stripping process. As a result, a compact Zn layer on Sn@Cu foam is obtained (Zn/Sn@Cu foam), symmetrical cells display superior cycling life of 1800 h at 1 mA cm−2 for 1 mAh cm−2, and full cells with VO2 cathode deliver remarkably better cycling stability and longer lifespan. [ABSTRACT FROM AUTHOR]

As a class of effective lightweight energy absorption materials, periodic closed-cell foams have been widely applied in engineering, in which the Kelvin and Octet-B foams have demonstrated great value in the research of multiaxial mechanical characteristics. For this reason, this study aims to develop a series of realistic finite element analysis (FEA) models for investigating their uniaxial, compression-shear, and arbitrary triaxial compression performance. Under uniaxial loading conditions, the mechanical responses and deformation modes of the two foams are compared and analyzed with different densities. The influence of different loading angles is also considered under compressive-shear loading. The deformation pattern of foams subject to equal biaxial and hydrostatic loading are compared with uniaxial compression. Based on sufficient simulation data, the initial yield surfaces of the two foams are plotted in the von Mises and mean stress plane, and fitted by three theoretical yield criteria characterized in terms of quadratic functions. It is found that the Miller criterion can better describe the initial yield surface shape of Kelvin foams than the yield models of Deshpande–Fleck and Zhang et al.; while the above yielding models are all of high fitting accuracy for the Octet-B foam. Further, the ability to resist initial yield of the Kelvin foam has proven superior to Octet-B foams by calculating the curve integration. The study is anticipated to provide new insights into novel design and extensive applications of periodic closed-cell foam materials in practice. • The realistic and systematic multiaxial simulation for polymetric foam. • Effect of relative density on mechanical performance of polymetric foam. • Effect of relative density on the initial yield surfaces of polymetric foam. • Identification of macroscopic yield constitutive relationship of polymetric foam. [ABSTRACT FROM AUTHOR]

The Co-Mo-Al and Co-Mo-Ce-Al catalysts were prepared and tested for their activity in the methanation of synthesis gas in the presence of hydrogen sulfide. The results showed that the Co-Mo-Ce-Al series was superior to the Co-Mo-Al system in terms of CO conversion. The former system was used to examine the main factors controlling the methanation behavior. Among these are: HS concentration in the reaction mixture, reaction temperature and pressure, concentrations of CO, CH, and HO, H/CO ratio, and gaseous hourly space velocity. The methanation activity increased with increasing temperature, pressure and H/CO ratio. The reason why adding CO or HO decreases the methanation activity is discussed. [ABSTRACT FROM AUTHOR]

• Temperature is one of the most important indicator to reflect the operating condition of dry-type transformers. • The Sparse Bayesian Learning algorithm is used to establish the temperature model. • The temperature range for the transformer under normal operating conditions is derived. • The temperature residual statistical analysis can distinguish the operating abnormalities from the measurement errors. In the offshore oil platform power system, the replacement of electric equipment is very inconvenient due to the far distance between the platform and the land. Transformer is one of the most important electric equipment in the oil power system, whose reliable operation is of essential importance to the normal oil exploitation. Therefore, the condition of the transformer should be monitored continuously to find out the possible operating abnormality as soon as possible. The transformer temperature is a good indicator to reflect the transformer operating condition. Moreover, there is a large amount of historical operating data provided by the monitoring system in the oil platform power system, which can be used as the basis to distinguish the normal and abnormal operating condition of the transformer. In this paper, an abnormal temperature pre-warning method is proposed for the dry-type transformer in the oil platform power system. Based on the historical operating data, the dry-type transformer temperature model is established by the Sparse Bayesian Learning. The proposed model provides a temperature warning range. By entering the current transformer operating parameters into the model, the temperature range for a normal operating state can be obtained. If the temperature measured by the transformer sensors exceed the expected ranges, an abnormality may occur. The residual statistical analysis is adopted to distinguish the measurement errors and actual transformer abnormal operations. The effectiveness and validity of the proposed method are verified based on the real field data of an oil platform transformer. [ABSTRACT FROM AUTHOR]

Mg is an important alloying element for Al anode in alkaline batteries. In this work, series of Al–Mg alloys have been investigated as anode materials, focusing on optimizing the Mg addition amount in Al anode with the intention of enhancing its discharge performance. The results show that solid-solute Mg improves the discharge potential of Al anode at low current density and inhibits its self-corrosion. However, excess Mg additions accelerate the self-corrosion of Al anode due to the formation of AlMg intermetallic in Al matrix. To reduce the corrosion rate and improve the discharge activity, Mg content in Al anode is optimized to be 0.5% with cooperation of electrolyte additive Na 2 SnO 3. • Effect of different Mg content on discharge performance of Al anode was investigated. • Mg addition in Al anode was optimized to be 0.5% at operating temperature of 50 °C. • Al-0.5 Mg exhibited coulombic efficiency of 96% at 100 mA cm−2, that of 5N Al was 83%. [ABSTRACT FROM AUTHOR]

Zn−Ni secondary battery is a promising candidate as next generation of energy storage battery. However, suffering from the poor cycle performance, its commercialization remains rather challenging. The severe dendrite growth of Zn anode and the rapid capacity decay caused by its uncontrollable dissolution and poor electronic conductivity of ZnO are the main factors. Herein, we report a novel Indium (In) doped ZnO/rGO anode material to inhibit ZnO dissolution through the generated C−O−Zn bond between ZnO and graphene. Meanwhile, the capacity decay decline due to the enhanced electronic conductivity of ZnO by the In doping and combination of graphene. As a result, In doped ZnO/rGO anode material delivers a high specific capacity of 643.4 mAh g−1 (coulombic efficiency 97.63 %) and remains 531.3 mAh g−1 after 125 cycles at 0.5 C, which are significantly higher than bare ZnO. [ABSTRACT FROM AUTHOR]

The 400 MeV LINAC1 of the proposed eRHIC collider1 is the first acceleration stage of the 18 GeV electron accelerator. The second acceleration stage of the electron accelerator is the Rapid Cycling Synchrotron (RCS), which can increase the energy of the electron bunches to 18 GeV and subsequently extract transfer and inject the 18 GeV electron bunches into the 18 GeV electron Storage Ring (SR) to collide with the hadron bunches of the existing (Relativistic Heavy Ion Collider (RHIC)) accelerator. This paper describes the beam optics of the transfer line between the 400 MeV LINAC and the RCS accelerator (LtRCS). The function of the LtRCS line is twofold, first to transfer the electron beam from the exit of the 400 MeV LINAC to the injection point of the RCS1 and second to rotate the stable spin direction of the polarized electrons from the longitudinal direction to the vertical. A detailed description of the constraints to be satisfied by the LtRCS transfer line will be given. A section will also be devoted to discuss the spin rotator2. [ABSTRACT FROM AUTHOR]

This paper introduces a novel hierarchical core structure to sandwich panel for bearing the blast loading, in which each vertex of a regular hexagonal cell was replaced with a smaller hexagonal unit. The finite element (FE) models of such hierarchical honeycomb sandwich panels were established and validated with the experiments under different impulse loads. The hierarchical honeycomb cores were compared with the regular honeycomb counterpart in terms of the peak deflection on the back facesheet, compression and specific energy absorption (SEA) of the core. The results showed that the maximum deflection at the back facesheet of the hierarchical honeycomb sandwich panels were smaller than the regular honeycomb counterpart for a higher level of blast load (specifically, the dimensionless impulse higher than 0.06). It was found that the structural hierarchical parameter γ (i.e. the ratio of the newly-introduced smaller hexagonal edge length (L 1) to the regular hexagon edge length (L 0)), had limited influence on the maximum deflection of back facesheet of the sandwich panel, but had a significant effect on the SEA of the cores. Image 1 • A novel sandwich panel with hierarchical honeycomb core for improving blast resistance was first developed. • Parametric study on blasting resistance of the novel sandwich panel was conducted. • The novel sandwich panel has excellent blasting resistance compared with traditional sandwich panel. [ABSTRACT FROM AUTHOR]

Abstract Aluminum is an attractive anode material for electrochemical energy storage and conversion devices, but the passive film and parasitic corrosion of aluminum anode in aqueous solution limits its development. Herein, we investigated the electrochemical performance of Al-2Mg alloy in alkaline electrolyte containing stannate ion via hydrogen evolution tests, electrochemical measurements and surface analysis. It is found that the solid-solute magnesium in aluminum matrix activates the oxide film and decreases the cathodic sites, which negatively shift the aluminum anode potential. Furthermore, the doping magnesium ion in the oxide film facilitates the tin deposition reaction on the surface of aluminum anode, and the uniformly deposited tin inhibits the parasitic corrosion reaction. As a result, Al-2Mg alloy in 6 M NaOH solution with 0.05 M Na 2 SnO 3 exhibits low hydrogen evolution rate of 0.015 mL·cm−2·min−1 with the inhibition efficiency of 95% at open circuit and negative electrode potential of −1.81 V vs. saturated calomel electrode at 20 mA cm−2. Highlights • The passivating oxide film of aluminum anode is doped with magnesium ion. • Magnesium ion activates the Al-2Mg anode in alkaline solution. • Tin is uniformly deposited on the Al-2Mg anode surface. • Al-2Mg in 6 M NaOH +0.05 M Na 2 SnO 3 exhibits high inhibition efficiency of 95%. • The anode possesses negative electrode potential of −1.81 V vs. SCE at 20 mA cm−2. [ABSTRACT FROM AUTHOR]

The constructed novel RMABs applying 1 M NaOH (aqueous)/"All in one" Mg anode electrolyte system with high reversibility and excellent cycle stability. [Display omitted] • "All in one" Mg anode is designed for RMABs. • 1 M NaOH (aqueous)/"All in one" Mg anode electrolyte system for RMABs is constructed. • High energy efficiency 69.7% and long lifespan of 506 h at 1 mA cm−2 are achieved. Rechargeable Magnesium-Air batteries (RMABs) are attracting significant attention for energy storage due to their uniqueness of high theoretical energy density, inherent safety and low cost. However, the exhibited poor energy efficiency as well as their short lifespan seriously hinder their further development. The main reason is that lacking a suitable electrolyte to balance the different needs of the cathode and anode, which can not only maintain the high reactivity of cathode but also achieving reversible stripping/plating of Mg anode and suppress its side reactions. To this end, we explored a novel "All in one" Mg anode and constructed a 1 M NaOH (aqueous)/"All in one" Mg anode electrolyte system for RMABs with high reversibility and excellent cycle stability. In particular, the unique design of "All in one" Mg anode which integrates Mg alloy layer, solid anolyte layer and ion exchange membrane layer, realizing the efficient reversible charge and discharge cycle of Mg anode in 1 M NaOH solution (catholyte). Thence, the availability of alkaline aqueous catholyte also preserve its high ORR/OER reactivity of air cathode, enabling the designed RMABs owns high energy efficiency 69.7% and long lifespan of 506 h at 1 mA cm−2. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mg anode in NaAc electrolyte exhibits uniform dissolution behavior. • Sufficiently inhibit the anodic hydrogen evolution corrosion of Mg anode. • Enhance the utilization efficiency of Mg anode up to 84% at 10 mA cm−2. • NaAc electrolyte is applied in a commercial Mg air battery. • Verify the anodic corrosion of Mg is related to its localized passive film rupture. Aqueous magnesium air batteries are promising energy conversion devices because of high theoretical energy density, inherent safety and low cost. However, their practical energy density is significantly limited due to the dramatic hydrogen evolution corrosion of Mg anode in conventional sodium chloride (NaCl) electrolyte. Herein, we suppress the hydrogen evolution reaction on the surface of Mg anode using sodium acetate (NaAc) electrolyte, in which Mg anode exhibits uniform anodic dissolution behavior without the notorious localized corrosion. It is demonstrated that acetate ion (Ac-) averts the localized passive film breakdown of Mg anode in virtue of its large diffusion energy barrier within the film. Therefore, the anodic hydrogen evolution phenomenon amid discharge is evidently repressed. This enables Mg anode to achieve a high utilization efficiency of 84 % at 10 mA cm−2 compared with 59 % in NaCl electrolyte. Mg air battery tests manifest that its specific energy based on the anode weight is boosted from 1370 to 1770 Wh kg−1. Finally, the practicality of NaAc electrolyte is confirmed in a commercial Mg air battery. This work provides a simple and scalable solution for high performance Mg air battery. [ABSTRACT FROM AUTHOR]

• The doping of Mn exposes more Co3+ active sites to enhance the ORR/OER activity. • The particle size of Mn-Co 3 O 4 nanoparticles was only about 5.5 nm. • Rechargeable ZAB displays a high-power density and superior cycling stability. High-performance and low-cost bifunctional electrocatalysts for ORR and OER are urgently required for rechargeable Zn-air batteries. Herein, a series of Mn-doped Co 3 O 4 nanoparticles grown on carbon nanotubes (Mn-Co 3 O 4 @CNTs) bifunctional electrocatalysts are designed. Owing to the moderate doped Mn atoms, the Mn-Co 3 O 4 heightens ORR activity via the synergistic effect between Co and Mn atoms, and more Co3+ active sites are exposed on the surface of Mn-Co 3 O 4 to enhance the OER rate. As a result, the 40% Mn-doped Mn-Co 3 O 4 @CNTs electrocatalyst exhibits higher ORR (E 1/2 = 0.84 V) and OER (η 10 = 356 mV at 10 mA cm−2) performance. More significantly, the Mn-Co 3 O 4 @CNTs equipped with rechargeable ZAB displays a high power density of 116 mW cm−2, a low charge-discharge voltage gap of 0.94 V at 10 mA cm−2, and superior cycling stability of over 425 h and 1200 cycles, being much more outperforming than Pt- and Ru-based ZABs. [Display omitted] [ABSTRACT FROM AUTHOR]

• Compared with hard classification method, the soft classification method can improve the performance of transformer diagnosis. • The probabilistic output result of three artificial algorithms is analyzed and compared. • Improved DS evidence theory can help to obtain a more accurate fault diagnosis result by combining mutiple probabilistic output models. Power transformer is one of the most vital equipment in the electric power systems, which serves as the connection of power networks at different voltage levels. However, the power transformers in service are subjected to various stresses like thermal stress and electrical stress, which may lead to several faults such as arching, partial discharge and overheating. In order to detect these incipient faults and ensure the normal operation of power transformers, the diagnostic methods based on Dissolved Gas Analysis (DGA) have been developed. However, the DGA methods suffer from low diagnostic accuracy. On the other hand, with the development of Artificial Intelligence (AI), a lot of intelligent algorithms have been applied in this area. However, most traditional AI algorithms are hard classification, which may cause the wrong diagnosis of faults. To overcome those disadvantages, a method based on the improved DS evidence theory and multiple probabilistic output algorithms is proposed in this paper to improve the performance of fault diagnosis of oil-immersed transformers. Firstly, the performance of the soft and hard classification algorithms is compared and analyzed. After that, three diagnostic models based on the Multiclass Relevance Vector Machine (MRVM), Multiclass Support Vector Machine (MSVM) and Back Propagation Neural Network (BPNN) are established. In order to improve the accuracy of these models, Particle Swarm Optimization (PSO) is used to optimize their hyper-parameters. Finally, the combination of these three probabilistic output models is achieved based on the improved Dempster-Shafer (DS) evidence theory, which can help to obtain a more accurate fault diagnosis result by fusing multiple algorithm results. The case study results show that the proposed method achieves a probabilistic output for the fault diagnosis of oil-immersed transformers and overcomes the deficiency of traditional DGA methods which are difficult to get accurate diagnosis results and can't summarize the fault development rule inductively. [ABSTRACT FROM AUTHOR]

Highlights: [•] The amide-groups are grafted over carbon surface via a simple solvothermal route. [•] Cobalt oxides of 2nm uniformly supporting on the carbon blacks were synthesized. [•] CoO x /XC N shows superior ORR activity than CoO x /XC and CoO x /XC O. [•] The enhanced ORR activity is contributed to the higher content of CoO in composite. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: A series of Ni modified MnO x /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 MnO x /C improves the distribution of the active material MnO x , which contributes to a surface with more MnOOH. The optimal composite is of the Ni/Mn atomic ratio of 1:2 and the MnO x loading of 28 wt.%. The maximum power density of the zinc–air battery with the optimized Ni modified MnO x /C as the cathode catalyst reaches up to 122 mW cm−2, much higher than the one with the MnO x /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. [Copyright &y& Elsevier]

Highlights: [•] The catalysts were prepared using sulfur powder as sulfiding agent. [•] The optimal sulfidation temperature was 450°C. [•] TM-MoS2 was more active because of structural similarity between ATM and MoS2. [•] The catalyst deactivation was due to the MoS2 crystal growth and structure change. [ABSTRACT FROM AUTHOR]

• Porous Ni(OH) 2 membrane resists phosphate but transfers OH− and H 2 • Phosphate ions directly participate in HER as reactant on Pt and Ni electrode • Phosphate ions enhance HER activity of Pt but lower HER activity for Ni electrode Phosphate buffer solution (PBS) is widely used in hydrogen evolution reaction (HER), however, the HER mechanism in PBS is still unclear whether the phosphate directly react with electrode like H 2 O. Herein, the porous and defective Ni(OH) 2 permselective membrane covered Pt and Ni electrode was fabricated by the electrodeposition method to identify the reaction mechanism. By obviously rejecting the phosphate and almost unimpededly transferring the OH−, H 2 O and H 2 , the membrane averts the contact of phosphate with the electrode surface without impeding of the necessary mass transfer of HER. Combining electrochemical analysis and theoretical calculation, the phosphate is found to be the HER reactant of Pt and Ni electrode in PBS. Detailly, the phosphate competes with H 2 O and accelerates the HER for Pt electrode, while poisons Ni electrode to deteriorate the HER performance. The Ni(OH) 2 membrane covered on HER electrode obviously rejects the transfer of phosphate, but almost unimpededly transfer the OH−, H 2 O and H 2 depending on the porous structure. These unique permselective feature helps to identify the HER mechanism in phosphate buffer solution. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

• Hollow carbon (HC) supported NiCo LDHs was synthesized via a solvothermal method. • High nickel concentration induces the uniform growth of a hydrangea-like structure. • Excessive divalent nickel ions contribute to higher pseudocapacitance. • The HC@NiCo LDHs electrode exhibits excellent capacitance of 758 C g−1 at 2 A g−1. Hydrangea-like hollow carbon shell-supported NiCo LDHs (HC@NiCo LDHs) have been readily synthesized via a chemical co-precipitation process without extra alkaline reagent added. Different molar ratios of Ni/Co (1:4, 2:3, 3:2 and 4:1) in the initial reactants were applied to explore its effect on a series of as-synthesized electrode materials. The optimized HC@NiCo LDHs with an actual Ni/Co molar ratio of ∼4.8:1 (reactant ratio of 4:1) exhibited the highest specific capacity of 758 C g−1 at 2 A g−1 and displayed excellent rate performance with 79% capacity retention at 20 A g−1. The much improved supercapacitive performance results from the high Ni concentration, which has induced the uniform growth and intimate contact of NiCo LDHs with weak crystallinity on hollow carbon shells to form a hydrangea-like structure. This unique structure and crystalline phase exposes more active sites and facilitates faster ion diffusion. Meanwhile, the Ni-rich NiCo LDHs increases divalent metal cations to achieve high pseudocapacitance. In addition, the assembled HC@NiCo LDHs//AC asymmetrical supercapacitor maintains 70% capacitance after 4000 cycles and possesses rapid electrokinetics. [Display omitted] [ABSTRACT FROM AUTHOR]