The growth of crystals of the high T c oxide superconductors has been hampe red by the complexities of the materials and their phase diagrams.The most common crys tal growth technique adopted for these oxides is the ...The growth of crystals of the high T c oxide superconductors has been hampe red by the complexities of the materials and their phase diagrams.The most common crys tal growth technique adopted for these oxides is the “flux”method,where the st arting materials are solved in a melt,which is usually formed by excess CuO and BaO or a KCl/NaCl mixture.The crystals are produced by slow cooling of the heate d solvent.This method,however,suffers from several disadvantages: (1) the crystals are contaminated with the crucible material, (2) the crystals are difficult to remove from the crucible, (3) the crystals contain flux inclusions.展开更多
Hydrogen evolution reaction is a critical reaction in water splitting for hydrogen production.However,developing effective and stable non‐noble‐metal electrocatalysts which work well at high current densities demand...Hydrogen evolution reaction is a critical reaction in water splitting for hydrogen production.However,developing effective and stable non‐noble‐metal electrocatalysts which work well at high current densities demanded by industry still remain great challenge.Herein,taking advantage of the highly tunable metal‐organic framework(MOF)templates,nitrogen doped binary transition metal phosphides electrocatalysts(N‐CoP_(x)/Ni_(2)P)with three‐dimensional(3D)conductive network structure were successfully synthesized.The 3D open porous channels could expose more catalytically active sites;nitrogen doping and the synergistic effect between CoP and Ni_(2)P can increase the electron density of Co atoms at active sites,further optimizing the Gibbs free energy of hydrogen(ΔGH*)and water(ΔG_(H_(2)O*)).As a result,the obtained N‐CoP_(x)/Ni_(2)P catalyst exhibits extraordinary electrocatalytic activity in a wide pH range.Especially,it requires an extremely low overpotential of 152 mV to deliver a high current density of 650 mA cm^(–2) in alkaline media.This work may shed some light on the rational design of cheap electrocatalysts and electrode materials that work well at high current densities.展开更多
The mechanical anisotropy,structural properties,electronic band structures and thermal properties of C2N2(CH2),Si2N2(SiH2)and Ge2N2(GeH2)are detailed and investigated in this work.The novel silicon nitride phase Si2N2...The mechanical anisotropy,structural properties,electronic band structures and thermal properties of C2N2(CH2),Si2N2(SiH2)and Ge2N2(GeH2)are detailed and investigated in this work.The novel silicon nitride phase Si2N2(SiH2)and germanium nitride phase Ge2N2(GeH2)in the Cmc21 structure are proposed in this work.The novel proposed Si2N2(SiH2)and Ge2N2(GeH2)are both mechanically and dynamically stable.The electronic band calculation of the HSE06 hybrid functional shows that C2N2(CH2),Si2N2(SiH2)and Ge2N2(GeH2)are all wide band gap semiconductor materials,and C2N2(CH2)and Si2N2(SiH2)are direct band gap semiconductor materials,while Ge2N2(GeH2)is a quasi-direct band gap semiconductor material,the band gap of C2N2(CH2),Si2N2(SiH2)and Ge2N2(GeH2)are 5.634 eV,3.013 eV,and2.377 eV,respectively.The three-dimensional and plane distributions of Young’s modulus,shear modulus and Poisson’s ratio of C2N2(CH2),Si2N2(SiH2)and Ge2N2(GeH2)show that these materials have different degrees of mechanical anisotropy.The order of Young’s modulus of Si2N2(SiH2)and Ge2N2(GeH2)in different directions is different from that of C2N2(CH2).When the tensile axis is in a particular direction,the order of the Young’s modulus of Si2N2(SiH2):E[110]<E[120]<E[111]<E[101]<E[010]=E[100]<E[011]<E[001],and the order of the Young’s modulus of Ge2N2(GeH2):E[110]<E[111]<E[101]<E[120]<E[100]<E[010]<E[011]<E[001].展开更多
文摘The growth of crystals of the high T c oxide superconductors has been hampe red by the complexities of the materials and their phase diagrams.The most common crys tal growth technique adopted for these oxides is the “flux”method,where the st arting materials are solved in a melt,which is usually formed by excess CuO and BaO or a KCl/NaCl mixture.The crystals are produced by slow cooling of the heate d solvent.This method,however,suffers from several disadvantages: (1) the crystals are contaminated with the crucible material, (2) the crystals are difficult to remove from the crucible, (3) the crystals contain flux inclusions.
文摘Hydrogen evolution reaction is a critical reaction in water splitting for hydrogen production.However,developing effective and stable non‐noble‐metal electrocatalysts which work well at high current densities demanded by industry still remain great challenge.Herein,taking advantage of the highly tunable metal‐organic framework(MOF)templates,nitrogen doped binary transition metal phosphides electrocatalysts(N‐CoP_(x)/Ni_(2)P)with three‐dimensional(3D)conductive network structure were successfully synthesized.The 3D open porous channels could expose more catalytically active sites;nitrogen doping and the synergistic effect between CoP and Ni_(2)P can increase the electron density of Co atoms at active sites,further optimizing the Gibbs free energy of hydrogen(ΔGH*)and water(ΔG_(H_(2)O*)).As a result,the obtained N‐CoP_(x)/Ni_(2)P catalyst exhibits extraordinary electrocatalytic activity in a wide pH range.Especially,it requires an extremely low overpotential of 152 mV to deliver a high current density of 650 mA cm^(–2) in alkaline media.This work may shed some light on the rational design of cheap electrocatalysts and electrode materials that work well at high current densities.
基金Project supported by the National Natural Science Foundation of China(grant numbers 61864004 and 61564005)。
文摘The mechanical anisotropy,structural properties,electronic band structures and thermal properties of C2N2(CH2),Si2N2(SiH2)and Ge2N2(GeH2)are detailed and investigated in this work.The novel silicon nitride phase Si2N2(SiH2)and germanium nitride phase Ge2N2(GeH2)in the Cmc21 structure are proposed in this work.The novel proposed Si2N2(SiH2)and Ge2N2(GeH2)are both mechanically and dynamically stable.The electronic band calculation of the HSE06 hybrid functional shows that C2N2(CH2),Si2N2(SiH2)and Ge2N2(GeH2)are all wide band gap semiconductor materials,and C2N2(CH2)and Si2N2(SiH2)are direct band gap semiconductor materials,while Ge2N2(GeH2)is a quasi-direct band gap semiconductor material,the band gap of C2N2(CH2),Si2N2(SiH2)and Ge2N2(GeH2)are 5.634 eV,3.013 eV,and2.377 eV,respectively.The three-dimensional and plane distributions of Young’s modulus,shear modulus and Poisson’s ratio of C2N2(CH2),Si2N2(SiH2)and Ge2N2(GeH2)show that these materials have different degrees of mechanical anisotropy.The order of Young’s modulus of Si2N2(SiH2)and Ge2N2(GeH2)in different directions is different from that of C2N2(CH2).When the tensile axis is in a particular direction,the order of the Young’s modulus of Si2N2(SiH2):E[110]<E[120]<E[111]<E[101]<E[010]=E[100]<E[011]<E[001],and the order of the Young’s modulus of Ge2N2(GeH2):E[110]<E[111]<E[101]<E[120]<E[100]<E[010]<E[011]<E[001].
