Perfluoroalkyl acids of different chain lengths,including trifluoroacetic acid,heptafluorobutyric acid,and nonafluoropentanoic acid,were used as second ligands to replace the formic acid on the Zr_(6)clusters in MOF-8...Perfluoroalkyl acids of different chain lengths,including trifluoroacetic acid,heptafluorobutyric acid,and nonafluoropentanoic acid,were used as second ligands to replace the formic acid on the Zr_(6)clusters in MOF-808.This led to the formation of a series of MOF-808-R materials(R=F_(3),F_(7),F_(9),corresponding to trifluoroacetic acid,hep-tafluorobutyric acid,and nonafluoropentanoic acid)with multiple ligands,and we investigated the impact of the sec-ond ligand modification on pore size and pore environment.The loading amount of the second ligand was deter-mined using NMR and other methods.We conducted adsorption tests for acetylene and carbon dioxide at different temperatures on both MOF-808 and MOF-808-R to explore the effects of the ligand diversification on acetylene sep-aration performance.It was found that MOF-808-F_(7)exhibited the best performance in acetylene-carbon dioxide sep-aration.展开更多
There is nonradiative recombination in waveguide region owing to severe carrier leakage,which in turn reduces output power and wall-plug efficiency.In this paper,we designed a novel epitaxial structure,which suppresse...There is nonradiative recombination in waveguide region owing to severe carrier leakage,which in turn reduces output power and wall-plug efficiency.In this paper,we designed a novel epitaxial structure,which suppresses carrier leakage by inserting n-Ga_(0.55)In_(0.45)P and p-GaAs_(0.6)P_(0.4) between barriers and waveguide layers,respectively,to modulate the energy band structure and to increase the height of barrier.The results show that the leakage current density reduces by 87.71%,compared to traditional structure.The nonradiative recombination current density of novel structure reduces to 37.411 A/cm^(2),and the output power reaches 12.80 W with wall-plug efficiency of 78.24%at an injection current density 5 A/cm^(2) at room temperature.In addition,the temperature drift coefficient of center wavelength is 0.206 nm/℃at the temperature range from 5℃to 65℃,and the slope of fitted straight line of threshold current with temperature variation is 0.00113.The novel epitaxial structure provides a theoretical basis for achieving high-power laser diode.展开更多
The large-scale commercialization of proton exchange membrane fuel cells(PEMFCs)has been hindered by the high demand of platinum(Pt)in the cathode due to the sluggish kinetics of the oxygen reduction reaction.Reducing...The large-scale commercialization of proton exchange membrane fuel cells(PEMFCs)has been hindered by the high demand of platinum(Pt)in the cathode due to the sluggish kinetics of the oxygen reduction reaction.Reducing the amount of Pt would worsen the problems caused by the adsorption of perfluorinated sulfonic acid(PFSA)ionomers to Pt via the side chains,namely,blocking the active sites of Pt and inducing densely packed layers of fluorocarbon backbones on Pt surface to obstruct local O_(2)transport at the Pt/PFSA interfaces.This work aims at optimizing the Pt/ionomer interface to mitigate the sulfonate adsorption and in the meantime to reduce the local O_(2)transport resistance(R_(local)),by using a porous composite of 1-butyl-3-methylimidazolium hydrogen sulfate ionic liquid(IL)modified MOF-808(BMImHSO_(4)@MOF-808)as additive in cathodic catalyst layer(CCL).Through detailed physical,spectroscopic and electrochemical characterizations,we demonstrate a three-fold optimization mechanism of Pt/ionomer interface structure by BMImHSO_(4)@MOF-808:the unsaturated metal sites in MOF-808 effectively inhibit the sulfonate adsorption on Pt through coordination with the sulfonates of PFSA,thereby improving catalyst utilization;the pores in MOF-808 establish efficient transport channels for gaseous oxygen,significantly reducing R_(local);the IL modification layers facilitate the formation of continuous proton transport networks,increasing proton conductivity.The incorporation of BMImHSO_(4)@MOF-808 in a low-Pt CCL(0.1 mg_(Pt)cm^(-2))yields a peak power density of 1.9 W cm^(-2)for PEMFC under H_(2)-O_(2)condition,and ca.20%increase of power density under H_(2)-air condition as compared with conventional CCL,indicating the prospect of IL-MOF composites as an efficient additive to enhance the performance of PEMFCs.展开更多
文摘Perfluoroalkyl acids of different chain lengths,including trifluoroacetic acid,heptafluorobutyric acid,and nonafluoropentanoic acid,were used as second ligands to replace the formic acid on the Zr_(6)clusters in MOF-808.This led to the formation of a series of MOF-808-R materials(R=F_(3),F_(7),F_(9),corresponding to trifluoroacetic acid,hep-tafluorobutyric acid,and nonafluoropentanoic acid)with multiple ligands,and we investigated the impact of the sec-ond ligand modification on pore size and pore environment.The loading amount of the second ligand was deter-mined using NMR and other methods.We conducted adsorption tests for acetylene and carbon dioxide at different temperatures on both MOF-808 and MOF-808-R to explore the effects of the ligand diversification on acetylene sep-aration performance.It was found that MOF-808-F_(7)exhibited the best performance in acetylene-carbon dioxide sep-aration.
文摘There is nonradiative recombination in waveguide region owing to severe carrier leakage,which in turn reduces output power and wall-plug efficiency.In this paper,we designed a novel epitaxial structure,which suppresses carrier leakage by inserting n-Ga_(0.55)In_(0.45)P and p-GaAs_(0.6)P_(0.4) between barriers and waveguide layers,respectively,to modulate the energy band structure and to increase the height of barrier.The results show that the leakage current density reduces by 87.71%,compared to traditional structure.The nonradiative recombination current density of novel structure reduces to 37.411 A/cm^(2),and the output power reaches 12.80 W with wall-plug efficiency of 78.24%at an injection current density 5 A/cm^(2) at room temperature.In addition,the temperature drift coefficient of center wavelength is 0.206 nm/℃at the temperature range from 5℃to 65℃,and the slope of fitted straight line of threshold current with temperature variation is 0.00113.The novel epitaxial structure provides a theoretical basis for achieving high-power laser diode.
文摘The large-scale commercialization of proton exchange membrane fuel cells(PEMFCs)has been hindered by the high demand of platinum(Pt)in the cathode due to the sluggish kinetics of the oxygen reduction reaction.Reducing the amount of Pt would worsen the problems caused by the adsorption of perfluorinated sulfonic acid(PFSA)ionomers to Pt via the side chains,namely,blocking the active sites of Pt and inducing densely packed layers of fluorocarbon backbones on Pt surface to obstruct local O_(2)transport at the Pt/PFSA interfaces.This work aims at optimizing the Pt/ionomer interface to mitigate the sulfonate adsorption and in the meantime to reduce the local O_(2)transport resistance(R_(local)),by using a porous composite of 1-butyl-3-methylimidazolium hydrogen sulfate ionic liquid(IL)modified MOF-808(BMImHSO_(4)@MOF-808)as additive in cathodic catalyst layer(CCL).Through detailed physical,spectroscopic and electrochemical characterizations,we demonstrate a three-fold optimization mechanism of Pt/ionomer interface structure by BMImHSO_(4)@MOF-808:the unsaturated metal sites in MOF-808 effectively inhibit the sulfonate adsorption on Pt through coordination with the sulfonates of PFSA,thereby improving catalyst utilization;the pores in MOF-808 establish efficient transport channels for gaseous oxygen,significantly reducing R_(local);the IL modification layers facilitate the formation of continuous proton transport networks,increasing proton conductivity.The incorporation of BMImHSO_(4)@MOF-808 in a low-Pt CCL(0.1 mg_(Pt)cm^(-2))yields a peak power density of 1.9 W cm^(-2)for PEMFC under H_(2)-O_(2)condition,and ca.20%increase of power density under H_(2)-air condition as compared with conventional CCL,indicating the prospect of IL-MOF composites as an efficient additive to enhance the performance of PEMFCs.
