Oxygen evolution reaction(OER)is the dominant step for plenty of energy conversion and storage technologies.However,the OER suffers from sluggish kinetics and high overpotential due to its complex 4‐electron/proton t...Oxygen evolution reaction(OER)is the dominant step for plenty of energy conversion and storage technologies.However,the OER suffers from sluggish kinetics and high overpotential due to its complex 4‐electron/proton transfer mechanism.Thus,developing efficient electrocatalysts is particularly urgent to accelerate OER catalysis but still remains a great challenge.Herein,we have synthesized the novel cobalt molybdate nanoflakes(CoMoO_(4)‐O_(v)‐n@GF)with adjustable oxygen vacancies contents by in situ constructing CoMoO_(4) nanoflakes on graphite felt(GF)and annealing treatment under the reduction atmosphere.The best‐performing CoMoO_(4)‐O_(v)‐2@GF with optimal oxygen vacancies content shows splendid electrocatalytic performance with the low overpotential(296 mV at 10 mA cm^(‒2))and also small Tafel slope(62.4 mV dec^(‒1))in alkaline solution,which are comparable to those of the RuO_(2)@GF.The experimental and the density functional theory calculations results reveal that the construction of optimal oxygen vacancies in CoMoO_(4) can expose more active sites,narrow the band‐gap to increase the electrical conductivity,and modulate the free energy of the OER‐related intermediates to accelerate OER kinetics,thus improving its intrinsic activity.展开更多
MoSi2 powders were fabricated respectively by mechanical alloying technique and sintering at different temperatures to prepare materials with different relative densities. The relative oxidation behavior of all MoSi2 ...MoSi2 powders were fabricated respectively by mechanical alloying technique and sintering at different temperatures to prepare materials with different relative densities. The relative oxidation behavior of all MoSi2 materials at 1 473 K was investigated by TGA,SEM and XRD. The results show that the "pesting" is not found in all materials after being oxidized for 480 h. The density has no essential relation to the "pesting". The oxidation curve of specimens with lower density shows two-step oxidation kinetics. Both the first stage (0-1 h) and the second stage (1-480 h) nearly obey linear kinetics,but the oxidation rates are obviously different. The oxidation kinetics of MoSi2 with higher relative density nearly follows parabolic law. The mass gains of MoSi2 with the lowest relative density (78.6%) and the highest relative density (94.8%) are increased by 10.390 and 0.135 mg/cm2,respectively. The oxide scale of materials with lower densities is non-protective and makes the oxygen diffusion easy. A dense scale in the material with higher density is formed,which acts as a diffusion barrier to the oxygen atoms to penetrate into the matrix,showing much better high temperature oxidation resistance. The phases distribution of oxidation scale from the outside to the inside is SiO2→Mo5Si3→MoSi2.展开更多
Using density functional theory calculations, we have investigated the mechanical properties and strain effects on the electronic structure and transport properties of molybdenum disulfide （MoS2） nanotubes. At a sim...Using density functional theory calculations, we have investigated the mechanical properties and strain effects on the electronic structure and transport properties of molybdenum disulfide （MoS2） nanotubes. At a similar diameter, an armchair nanotube has a higher Young＇s modulus and Poisson ratio than its zigzag counterpart due to the different orientations of Mo-S bond topologies. An increase in axial tensile strain leads to a progressive decrease in the band gap for both armchair and zigzag nanotubes. For armchair nanotube, however, there is a semiconductor-to-metal transition at the tensile strain of about 8%. For both armchair and zigzag nanotubes, the effective mass of a hole is uniformly larger than its electron counterpart, and is more sensitive to strain. Based on deformation potential theory, we have calculated the carrier mobilities of MoS2 nanotubes. It is found that the hole mobility is higher than its electron counterpart for armchair （6, 6） nanotube while the electron mobility is higher than its hole counterpart for zigzag （10, 0） nanotube. Our results highlight the tunable electronic properties of MoS2 nanotubes, promising for interesting applications in nanodevices, such as opto-electronics, photoluminescence, electronic switch and nanoscale strain sensor.展开更多
文摘Oxygen evolution reaction(OER)is the dominant step for plenty of energy conversion and storage technologies.However,the OER suffers from sluggish kinetics and high overpotential due to its complex 4‐electron/proton transfer mechanism.Thus,developing efficient electrocatalysts is particularly urgent to accelerate OER catalysis but still remains a great challenge.Herein,we have synthesized the novel cobalt molybdate nanoflakes(CoMoO_(4)‐O_(v)‐n@GF)with adjustable oxygen vacancies contents by in situ constructing CoMoO_(4) nanoflakes on graphite felt(GF)and annealing treatment under the reduction atmosphere.The best‐performing CoMoO_(4)‐O_(v)‐2@GF with optimal oxygen vacancies content shows splendid electrocatalytic performance with the low overpotential(296 mV at 10 mA cm^(‒2))and also small Tafel slope(62.4 mV dec^(‒1))in alkaline solution,which are comparable to those of the RuO_(2)@GF.The experimental and the density functional theory calculations results reveal that the construction of optimal oxygen vacancies in CoMoO_(4) can expose more active sites,narrow the band‐gap to increase the electrical conductivity,and modulate the free energy of the OER‐related intermediates to accelerate OER kinetics,thus improving its intrinsic activity.
基金Project(50405041) supported by the National Natural Science Foundation of ChinaProject(06C316) supported by the Scientific Research Fund of Hunan Provincial Education Deparment, China
文摘MoSi2 powders were fabricated respectively by mechanical alloying technique and sintering at different temperatures to prepare materials with different relative densities. The relative oxidation behavior of all MoSi2 materials at 1 473 K was investigated by TGA,SEM and XRD. The results show that the "pesting" is not found in all materials after being oxidized for 480 h. The density has no essential relation to the "pesting". The oxidation curve of specimens with lower density shows two-step oxidation kinetics. Both the first stage (0-1 h) and the second stage (1-480 h) nearly obey linear kinetics,but the oxidation rates are obviously different. The oxidation kinetics of MoSi2 with higher relative density nearly follows parabolic law. The mass gains of MoSi2 with the lowest relative density (78.6%) and the highest relative density (94.8%) are increased by 10.390 and 0.135 mg/cm2,respectively. The oxide scale of materials with lower densities is non-protective and makes the oxygen diffusion easy. A dense scale in the material with higher density is formed,which acts as a diffusion barrier to the oxygen atoms to penetrate into the matrix,showing much better high temperature oxidation resistance. The phases distribution of oxidation scale from the outside to the inside is SiO2→Mo5Si3→MoSi2.
文摘Using density functional theory calculations, we have investigated the mechanical properties and strain effects on the electronic structure and transport properties of molybdenum disulfide （MoS2） nanotubes. At a similar diameter, an armchair nanotube has a higher Young＇s modulus and Poisson ratio than its zigzag counterpart due to the different orientations of Mo-S bond topologies. An increase in axial tensile strain leads to a progressive decrease in the band gap for both armchair and zigzag nanotubes. For armchair nanotube, however, there is a semiconductor-to-metal transition at the tensile strain of about 8%. For both armchair and zigzag nanotubes, the effective mass of a hole is uniformly larger than its electron counterpart, and is more sensitive to strain. Based on deformation potential theory, we have calculated the carrier mobilities of MoS2 nanotubes. It is found that the hole mobility is higher than its electron counterpart for armchair （6, 6） nanotube while the electron mobility is higher than its hole counterpart for zigzag （10, 0） nanotube. Our results highlight the tunable electronic properties of MoS2 nanotubes, promising for interesting applications in nanodevices, such as opto-electronics, photoluminescence, electronic switch and nanoscale strain sensor.
