Herein,ionomer-free amorphous iridium oxide(IrO_(x))thin electrodes are first developed as highly active anodes for proton exchange membrane electrolyzer cells(PEMECs)via low-cost,environmentally friendly,and easily s...Herein,ionomer-free amorphous iridium oxide(IrO_(x))thin electrodes are first developed as highly active anodes for proton exchange membrane electrolyzer cells(PEMECs)via low-cost,environmentally friendly,and easily scalable electrodeposition at room temperature.Combined with a Nafion 117 membrane,the IrO_(x)-integrated electrode with an ultralow loading of 0.075 mg cm^(-2)delivers a high cell efficiency of about 90%,achieving more than 96%catalyst savings and 42-fold higher catalyst utilization compared to commercial catalyst-coated membrane(2 mg cm^(-2)).Additionally,the IrO_(x)electrode demonstrates superior performance,higher catalyst utilization and significantly simplified fabrication with easy scalability compared with the most previously reported anodes.Notably,the remarkable performance could be mainly due to the amorphous phase property,sufficient Ir^(3+)content,and rich surface hydroxide groups in catalysts.Overall,due to the high activity,high cell efficiency,an economical,greatly simplified and easily scalable fabrication process,and ultrahigh material utilization,the IrO_(x)electrode shows great potential to be applied in industry and accelerates the commercialization of PEMECs and renewable energy evolution.展开更多
Recent research is summarised with an emphasis on the use of Mg alloys for biodegradable medical applications.Mg melt purification using Zr has been shown to provide the opportunity to produce ultra-high-purity Mg all...Recent research is summarised with an emphasis on the use of Mg alloys for biodegradable medical applications.Mg melt purification using Zr has been shown to provide the opportunity to produce ultra-high-purity Mg alloys,which could lead to stainless Mg.Nor's solution may be a good starting model for the study of Mg for biodegradable medical implant applications.A systematic laboratory investigation is needed to elucidate the details of how the corrosion behaviour is controlled by the various constituents of the body fluids.In the evaluation of the Mg corrosion mechanism there is a critical lack of understanding of(i)the amount of hydrogen dissolved in the Mg metal during corrosion,and during anodic polarisation,and(ii)the size film-free area where corrosion occurs,and how to measure this area.In the evaluation of the apparent valence of Mg using an applied anodic current density,for reliable values,it is important to apply a sufficiently large applied current density.The available data are consistent with the slightly modified uni-positive Mg^(+)ion mechanism,which maintains that(i)the surface of Mg is covered by a partially protective film,and the film-free area increases as the potential becomes more positive(i.e.a catalytic activation process),(ii)corrosion occurs preferentially at breaks in the partial protective film,(iii)corrosion at the breaks in the partially protective film involves the uni-positive Mg ion,(iv)undermining of particles occurs when Mg is severely dissolved,and(v)there may be some self-corrosion not covered by these four processes,which may be associated with crevice-like features on a severely corroded surface or hydride dissolution at relatively negative potentials.Self-corrosion might also be possible under condition of essentially uniform corrosion.Mg^(+)has not been experimentally observed.Its existence is postulated as an extremely-short lifetime intermediate in the reaction sequence between metallic Mg and the equilibrium ion Mg^(++).There has been no direct experimental examination of this sequence,and a key challenge remains to devise an experimental approach to study the details of this reaction sequence and the intermediate steps.The apparent valence of Mg continues to be a critical question.If defendable values of effective valence for Mg less than 1.0 were measured,this would indicate that some phenomena contribute to these low values that are not currently accounted for in the uni-positive Mg^(+)corrosion mechanism.The most likely candidate would be self-corrosion.展开更多
Two-dimensional layers of metal dichalcogenides have attracted much attention because of their ultrathin thickness and potential applications in electronics and optoelectronics. Monolayer SnS2, with a band gap of -2.6...Two-dimensional layers of metal dichalcogenides have attracted much attention because of their ultrathin thickness and potential applications in electronics and optoelectronics. Monolayer SnS2, with a band gap of -2.6 eV, has an octahedral lattice made of two atomic layers of sulfur and one atomic layer of tin. Till date, there have been limited reports on the growth of large-scale and high quality SnS2 atomic layers and the investigation of their properties as a semiconductor. Here, we report the chemical vapor deposition （CVD） growth of atomic-layer SnS2 with a large crystal size and uniformity. In addition, the number of layers can be changed from a monolayer to few layers and to bulk by changing the growth time. Scanning transmission electron microscopy was used to analyze the atomic structure and demonstrate the 2H stacking poly-type of different layers. The resultant SnS2 crystals is used as a photodetector with external quantum efficiency as high as 150%, suggesting promise for optoelectronic applications.展开更多
A sparse-grid method for solving multi-dimensional backward stochastic differential equations （BSDEs） based on a multi-step time discretization scheme [31] is presented. In the multi-dimensional spatial domain, i.e....A sparse-grid method for solving multi-dimensional backward stochastic differential equations （BSDEs） based on a multi-step time discretization scheme [31] is presented. In the multi-dimensional spatial domain, i.e. the Brownian space, the conditional mathe- matical expectations derived from the original equation are approximated using sparse-grid Gauss-Hermite quadrature rule and （adaptive） hierarchical sparse-grid interpolation. Error estimates are proved for the proposed fully-discrete scheme for multi-dimensional BSDEs with certain types of simplified generator functions. Finally, several numerical examples are provided to illustrate the accuracy and efficiency of our scheme.展开更多
Medium-voltage(MV)power electronics equipment has been increasingly applied m distnbution grids,and high-voltage(HV)silicon carbide(SiC)power semiconductors have attracted considerable attention in recent years.This p...Medium-voltage(MV)power electronics equipment has been increasingly applied m distnbution grids,and high-voltage(HV)silicon carbide(SiC)power semiconductors have attracted considerable attention in recent years.This paper first overviews the development and status of HV SiC power semiconductors.Then,MV power-converter applications in distribution grids are summarized and the benefits of HV SiC in these applications are presented.Microgrids,including conventional and asynchronous microgrids,that can fully demonstrate the benefits of HV SiC power semiconductors are selected to investigate the benefits of HV SiC in detail,including converter-level benefits and system-level benefits.Finally,an asynchronous microgrid power-conditioning system(PCS)prototype using a 10 kV SiC MOSFET is presented.展开更多
The transverse emittance of an ion beam describes its transverse size as the particles are transported from a source to a target.It allows for predicting beam losses in limiting apertures and the beam focus size at th...The transverse emittance of an ion beam describes its transverse size as the particles are transported from a source to a target.It allows for predicting beam losses in limiting apertures and the beam focus size at the target.Various definitions and issues are discussed.The most common and emerging measuring techniques are presented,including their advantages.Several methods of emittance data analysis,their accuracy and trustworthiness,are discussed.展开更多
As a visible-light response photocatalyst,BiVO_(4)is widely used in photocatalytic oxygen evolution.In this study,a novel BiVO_(4)-Bi_(6)O_(6)(OH)_(3)(NO_(3))_(3)(BBN)heterostructure fabricates via a simple one-pot hy...As a visible-light response photocatalyst,BiVO_(4)is widely used in photocatalytic oxygen evolution.In this study,a novel BiVO_(4)-Bi_(6)O_(6)(OH)_(3)(NO_(3))_(3)(BBN)heterostructure fabricates via a simple one-pot hydrothermal approach is certified to effectively restrain the recombination of carriers by efficient spatial charge separation.By employing BBN as a reductive-function photocatalyst,a solid-state Z-scheme is constructed to improve the photo-redox capacity of BiVO_(4)and hydrogen production is realized in the BiVO_(4)-BBN heterostructure for the first time.The solid-state Z-scheme introduced in the BiVO_(4)-BBN ensures the photoexcited carriers with the powerful redox capacity to participate in the photocatalytic reaction.展开更多
基金the support from the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Hydrogen and Fuel Cell Technologies Office Awards DE-EE0008426 and DE-EE0008423National Energy Technology Laboratory under Award DEFE0011585.
文摘Herein,ionomer-free amorphous iridium oxide(IrO_(x))thin electrodes are first developed as highly active anodes for proton exchange membrane electrolyzer cells(PEMECs)via low-cost,environmentally friendly,and easily scalable electrodeposition at room temperature.Combined with a Nafion 117 membrane,the IrO_(x)-integrated electrode with an ultralow loading of 0.075 mg cm^(-2)delivers a high cell efficiency of about 90%,achieving more than 96%catalyst savings and 42-fold higher catalyst utilization compared to commercial catalyst-coated membrane(2 mg cm^(-2)).Additionally,the IrO_(x)electrode demonstrates superior performance,higher catalyst utilization and significantly simplified fabrication with easy scalability compared with the most previously reported anodes.Notably,the remarkable performance could be mainly due to the amorphous phase property,sufficient Ir^(3+)content,and rich surface hydroxide groups in catalysts.Overall,due to the high activity,high cell efficiency,an economical,greatly simplified and easily scalable fabrication process,and ultrahigh material utilization,the IrO_(x)electrode shows great potential to be applied in industry and accelerates the commercialization of PEMECs and renewable energy evolution.
基金This research was supported by the Australian Research Council Centre of Excellence Design of Light Alloys.Thanks to the China Scholarship Council to provide a scholarship under the State Scholarship Fund to Fuyong Cao.
文摘Recent research is summarised with an emphasis on the use of Mg alloys for biodegradable medical applications.Mg melt purification using Zr has been shown to provide the opportunity to produce ultra-high-purity Mg alloys,which could lead to stainless Mg.Nor's solution may be a good starting model for the study of Mg for biodegradable medical implant applications.A systematic laboratory investigation is needed to elucidate the details of how the corrosion behaviour is controlled by the various constituents of the body fluids.In the evaluation of the Mg corrosion mechanism there is a critical lack of understanding of(i)the amount of hydrogen dissolved in the Mg metal during corrosion,and during anodic polarisation,and(ii)the size film-free area where corrosion occurs,and how to measure this area.In the evaluation of the apparent valence of Mg using an applied anodic current density,for reliable values,it is important to apply a sufficiently large applied current density.The available data are consistent with the slightly modified uni-positive Mg^(+)ion mechanism,which maintains that(i)the surface of Mg is covered by a partially protective film,and the film-free area increases as the potential becomes more positive(i.e.a catalytic activation process),(ii)corrosion occurs preferentially at breaks in the partial protective film,(iii)corrosion at the breaks in the partially protective film involves the uni-positive Mg ion,(iv)undermining of particles occurs when Mg is severely dissolved,and(v)there may be some self-corrosion not covered by these four processes,which may be associated with crevice-like features on a severely corroded surface or hydride dissolution at relatively negative potentials.Self-corrosion might also be possible under condition of essentially uniform corrosion.Mg^(+)has not been experimentally observed.Its existence is postulated as an extremely-short lifetime intermediate in the reaction sequence between metallic Mg and the equilibrium ion Mg^(++).There has been no direct experimental examination of this sequence,and a key challenge remains to devise an experimental approach to study the details of this reaction sequence and the intermediate steps.The apparent valence of Mg continues to be a critical question.If defendable values of effective valence for Mg less than 1.0 were measured,this would indicate that some phenomena contribute to these low values that are not currently accounted for in the uni-positive Mg^(+)corrosion mechanism.The most likely candidate would be self-corrosion.
文摘Two-dimensional layers of metal dichalcogenides have attracted much attention because of their ultrathin thickness and potential applications in electronics and optoelectronics. Monolayer SnS2, with a band gap of -2.6 eV, has an octahedral lattice made of two atomic layers of sulfur and one atomic layer of tin. Till date, there have been limited reports on the growth of large-scale and high quality SnS2 atomic layers and the investigation of their properties as a semiconductor. Here, we report the chemical vapor deposition （CVD） growth of atomic-layer SnS2 with a large crystal size and uniformity. In addition, the number of layers can be changed from a monolayer to few layers and to bulk by changing the growth time. Scanning transmission electron microscopy was used to analyze the atomic structure and demonstrate the 2H stacking poly-type of different layers. The resultant SnS2 crystals is used as a photodetector with external quantum efficiency as high as 150%, suggesting promise for optoelectronic applications.
基金Acknowledgments. The first author was supported by the US Air Force Office of Scientific Research under grant FA9550-11-1-0149. The first author was also supported by the Advanced Simulation Computing Research （ASCR）, Department of Energy, through the Householder Fellowship at ORNL. The ORNL is operated by UT-Battelle, LLC, for the United States Depart-ment of Energy under Contract DE-AC05-00OR22725. The second author was supported by the US Air Force Office of Scientific Research under grant FA9550-11-1-0149. The third author was supported by the Natural Science Foundation of China under grant 11171189. The third author was also supported by the Natural Science Foundation of China under grant 91130003. The thrid author was also supported by Shandong Province Natural Science Foundation under grant ZR2001AZ002.
文摘A sparse-grid method for solving multi-dimensional backward stochastic differential equations （BSDEs） based on a multi-step time discretization scheme [31] is presented. In the multi-dimensional spatial domain, i.e. the Brownian space, the conditional mathe- matical expectations derived from the original equation are approximated using sparse-grid Gauss-Hermite quadrature rule and （adaptive） hierarchical sparse-grid interpolation. Error estimates are proved for the proposed fully-discrete scheme for multi-dimensional BSDEs with certain types of simplified generator functions. Finally, several numerical examples are provided to illustrate the accuracy and efficiency of our scheme.
基金Supported by the DOE through Oak Ridge National Lab and the Power America Program,the Engineering Research Center Program of the National Science Foundation,and the CURENT Industry Partnership Program.
文摘Medium-voltage(MV)power electronics equipment has been increasingly applied m distnbution grids,and high-voltage(HV)silicon carbide(SiC)power semiconductors have attracted considerable attention in recent years.This paper first overviews the development and status of HV SiC power semiconductors.Then,MV power-converter applications in distribution grids are summarized and the benefits of HV SiC in these applications are presented.Microgrids,including conventional and asynchronous microgrids,that can fully demonstrate the benefits of HV SiC power semiconductors are selected to investigate the benefits of HV SiC in detail,including converter-level benefits and system-level benefits.Finally,an asynchronous microgrid power-conditioning system(PCS)prototype using a 10 kV SiC MOSFET is presented.
基金ORNL/SNS is managed by UT-Battelle,LLC,for the U.S.Department of Energy under contract DE-AC05-00OR22725
文摘The transverse emittance of an ion beam describes its transverse size as the particles are transported from a source to a target.It allows for predicting beam losses in limiting apertures and the beam focus size at the target.Various definitions and issues are discussed.The most common and emerging measuring techniques are presented,including their advantages.Several methods of emittance data analysis,their accuracy and trustworthiness,are discussed.
基金the National Natural Science Foundation of China(Nos.51862023,51662030 and 21868016)the Natural Science Foundation of Jiangxi Province(No.20171BAB206014)。
文摘As a visible-light response photocatalyst,BiVO_(4)is widely used in photocatalytic oxygen evolution.In this study,a novel BiVO_(4)-Bi_(6)O_(6)(OH)_(3)(NO_(3))_(3)(BBN)heterostructure fabricates via a simple one-pot hydrothermal approach is certified to effectively restrain the recombination of carriers by efficient spatial charge separation.By employing BBN as a reductive-function photocatalyst,a solid-state Z-scheme is constructed to improve the photo-redox capacity of BiVO_(4)and hydrogen production is realized in the BiVO_(4)-BBN heterostructure for the first time.The solid-state Z-scheme introduced in the BiVO_(4)-BBN ensures the photoexcited carriers with the powerful redox capacity to participate in the photocatalytic reaction.
