Pyrochlore-type WO3 powder was synthesized via hydrothermal method using aqueous sodium tungstate solution and oxalic acid as raw materials. The as-prepared powder was made into a soliquoid, from which films were made...Pyrochlore-type WO3 powder was synthesized via hydrothermal method using aqueous sodium tungstate solution and oxalic acid as raw materials. The as-prepared powder was made into a soliquoid, from which films were made by dip coating process with indium-tin oxide （ITO）. The obtained films were characterized by thermogravimetric and differential thermal analysis （TG-DTA）, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, cyclic voltammetry （CV）, chronoamperometry （CA） and ultraviolet- visible （UV-Vis） absorption. Results show that the crystal of the pyrochlore-type WO3 powder is perfect. When the calcination temperature rises from room temperature to 500℃, the pyrochlore-type structure first becomes deformed, then it is destroyed and turns into amorphous phase, finally it will completely convert to WO3 with a monoclinic structure. Electrochemical and optical tests demonstrate that the film calcined at 300℃ exhibits the best electrochromic performance and has a coloration efficiency of up to 68.5 cm^2-C^-1 at 884 nm.展开更多
Pyrochlore-type tungsten oxide (PTO), WO3·0.5H2O, is an emerging material with very wide potential applications. The influences of iron valences and the additive amount of ferrous ion on tungsten crystallization ...Pyrochlore-type tungsten oxide (PTO), WO3·0.5H2O, is an emerging material with very wide potential applications. The influences of iron valences and the additive amount of ferrous ion on tungsten crystallization ratio and the acceleration mechanism of ferrous ion were investigated when PTO was hydrothermally prepared in aqueous ammonium tungstate solution containing ammonium carbonate. The results show that ferrous ion can remarkably accelerate tungsten crystallization while both elemental iron and ferric ion have little influence on the crystallization. Moreover, the tungsten crystallization ratio increases with increasing the amount of ferrous ions added and reaches the maximum of about 60% with ferrous ion concentration of 16 g/L. FTIR analysis of the spent solution after PTO crystallization shows that ferrous ion can accelerate the conversion of WO4 tetrahedral to WO6 octahedron. Combined with XPS and XRD analyses of the hydrothermal product, the acceleration effect of ferrous ion on tungsten crystallization could basically be attributed to the increase in the interplanar spacing of PTO lattice caused by the incorporation of ferrous ion into PTO crystal lattice. The results presented is conducive to the efficient preparation of PTO powder and cleaner tungsten metallurgy.展开更多
Sodium-ion batteries hold significant potential for large-scale energy storage applications,primarily because of their impressive energy density.Massive researches on anode materials mainly focus on carbon materials b...Sodium-ion batteries hold significant potential for large-scale energy storage applications,primarily because of their impressive energy density.Massive researches on anode materials mainly focus on carbon materials because of their high theoretical capacity and affordability.Nevertheless,the large volume change of carbon materials during the sodium ion intercalation/de-intercalation processes seriously influences their electrochemical properties and limits their practical applications.Finding stable and high performance materials remains a significant challenge in the progress of NIBs development.Herein,a pyrochlore-type oxide(A_(2)B_(2)O_(7))for sodium storage is successfully synthesized in this work,which adopts a“zigzag”structure of AO_(6) octahedra and BO_(4) tetrahedra.Density functional theory calculations and structural characterizations indicate that the material is able to host Na ions in the structure properly and maintains excellent structural stability during the intercalation and deintercalation of Na^(+),making the pyrochlore-type oxide an excellent Na storage material.Electrochemical measurements indicate that the pyrochlore-type oxide exhibits excellent electrochemical performances and extremely stable sodium storage ability(high capacity of~250 mAh g^(-1)at 30 mA g^(-1),~85% capacity retention after 25000 cycles at 5 A g^(-1)).In addition,the full cell shows excellent electrochemical performances in all climatic operation temperature ranges from-30℃ to 40℃(117 mAh g^(-1)at 40℃ and 103 mAh g^(-1)at-30℃).The high reversible capacity,impressive rate capability and outstanding cycling stability demonstrated by pyrochlore-type oxides make them a competitive choice among Na-ion anode materials.This study introduces a new type of pyrochlore-type transition metal oxide for stable Na storage,which shows high capacity,excellent rate performances and extremely long cycling life.This study is expected to significantly advance the development of anode for NIBs.展开更多
The effects of temperature, ammonia concentration and ammonium carbonate concentration on the dissolving behavior of ammonium paratungstate were studied in（NH4）2CO3-NH3？H2O-H2O system. The results show that rising ...The effects of temperature, ammonia concentration and ammonium carbonate concentration on the dissolving behavior of ammonium paratungstate were studied in（NH4）2CO3-NH3？H2O-H2O system. The results show that rising temperature, prolonging duration, increasing ammonia concentration and decreasing ammonium carbonate concentration favor dissolving of ammonium paratungstate at temperature below 90 ℃, while the WO3 concentration decreases after a certain time at temperature above 100 ℃. Furthermore, the undissolved tungsten exists in the form of either APT·4 H2O below 90 ℃ or pyrochlore-type tungsten trioxide above 100℃. In dissolving process, the ammonium paratungstate dissolves into paratungstate ions followed by partially converting to tungstate ion, resulting in the coexistence of the both ions. This study may provide a new idea to exploit a novel technique for manufacturing ammonium paratungstate and pyrochlore-type tungsten trioxide.展开更多
基金financially supported by the National Natural Science Foundation of China (No. 51274243)the Project of Innovation-Driven Plan in Central South University, China (No. 2015CX001)
文摘Pyrochlore-type WO3 powder was synthesized via hydrothermal method using aqueous sodium tungstate solution and oxalic acid as raw materials. The as-prepared powder was made into a soliquoid, from which films were made by dip coating process with indium-tin oxide （ITO）. The obtained films were characterized by thermogravimetric and differential thermal analysis （TG-DTA）, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, cyclic voltammetry （CV）, chronoamperometry （CA） and ultraviolet- visible （UV-Vis） absorption. Results show that the crystal of the pyrochlore-type WO3 powder is perfect. When the calcination temperature rises from room temperature to 500℃, the pyrochlore-type structure first becomes deformed, then it is destroyed and turns into amorphous phase, finally it will completely convert to WO3 with a monoclinic structure. Electrochemical and optical tests demonstrate that the film calcined at 300℃ exhibits the best electrochromic performance and has a coloration efficiency of up to 68.5 cm^2-C^-1 at 884 nm.
基金Project(51274243) supported by the National Natural Science Foundation of China
文摘Pyrochlore-type tungsten oxide (PTO), WO3·0.5H2O, is an emerging material with very wide potential applications. The influences of iron valences and the additive amount of ferrous ion on tungsten crystallization ratio and the acceleration mechanism of ferrous ion were investigated when PTO was hydrothermally prepared in aqueous ammonium tungstate solution containing ammonium carbonate. The results show that ferrous ion can remarkably accelerate tungsten crystallization while both elemental iron and ferric ion have little influence on the crystallization. Moreover, the tungsten crystallization ratio increases with increasing the amount of ferrous ions added and reaches the maximum of about 60% with ferrous ion concentration of 16 g/L. FTIR analysis of the spent solution after PTO crystallization shows that ferrous ion can accelerate the conversion of WO4 tetrahedral to WO6 octahedron. Combined with XPS and XRD analyses of the hydrothermal product, the acceleration effect of ferrous ion on tungsten crystallization could basically be attributed to the increase in the interplanar spacing of PTO lattice caused by the incorporation of ferrous ion into PTO crystal lattice. The results presented is conducive to the efficient preparation of PTO powder and cleaner tungsten metallurgy.
文摘Sodium-ion batteries hold significant potential for large-scale energy storage applications,primarily because of their impressive energy density.Massive researches on anode materials mainly focus on carbon materials because of their high theoretical capacity and affordability.Nevertheless,the large volume change of carbon materials during the sodium ion intercalation/de-intercalation processes seriously influences their electrochemical properties and limits their practical applications.Finding stable and high performance materials remains a significant challenge in the progress of NIBs development.Herein,a pyrochlore-type oxide(A_(2)B_(2)O_(7))for sodium storage is successfully synthesized in this work,which adopts a“zigzag”structure of AO_(6) octahedra and BO_(4) tetrahedra.Density functional theory calculations and structural characterizations indicate that the material is able to host Na ions in the structure properly and maintains excellent structural stability during the intercalation and deintercalation of Na^(+),making the pyrochlore-type oxide an excellent Na storage material.Electrochemical measurements indicate that the pyrochlore-type oxide exhibits excellent electrochemical performances and extremely stable sodium storage ability(high capacity of~250 mAh g^(-1)at 30 mA g^(-1),~85% capacity retention after 25000 cycles at 5 A g^(-1)).In addition,the full cell shows excellent electrochemical performances in all climatic operation temperature ranges from-30℃ to 40℃(117 mAh g^(-1)at 40℃ and 103 mAh g^(-1)at-30℃).The high reversible capacity,impressive rate capability and outstanding cycling stability demonstrated by pyrochlore-type oxides make them a competitive choice among Na-ion anode materials.This study introduces a new type of pyrochlore-type transition metal oxide for stable Na storage,which shows high capacity,excellent rate performances and extremely long cycling life.This study is expected to significantly advance the development of anode for NIBs.
基金Project(51274243) supported by the National Natural Science Foundation of China
文摘The effects of temperature, ammonia concentration and ammonium carbonate concentration on the dissolving behavior of ammonium paratungstate were studied in（NH4）2CO3-NH3？H2O-H2O system. The results show that rising temperature, prolonging duration, increasing ammonia concentration and decreasing ammonium carbonate concentration favor dissolving of ammonium paratungstate at temperature below 90 ℃, while the WO3 concentration decreases after a certain time at temperature above 100 ℃. Furthermore, the undissolved tungsten exists in the form of either APT·4 H2O below 90 ℃ or pyrochlore-type tungsten trioxide above 100℃. In dissolving process, the ammonium paratungstate dissolves into paratungstate ions followed by partially converting to tungstate ion, resulting in the coexistence of the both ions. This study may provide a new idea to exploit a novel technique for manufacturing ammonium paratungstate and pyrochlore-type tungsten trioxide.
