The electrochemical storage of energy in a special kind of active carbon materials used as capacitor electrodes is considered. Petroleum coke was used for preparation of carbons with different porosities by KOH and va...The electrochemical storage of energy in a special kind of active carbon materials used as capacitor electrodes is considered. Petroleum coke was used for preparation of carbons with different porosities by KOH and vapor etching with catalysis of FeCI3 in turn. Carbon electrodes were fabricated and used as electrodes of double layer capacitors. Nitrogen adsorption was used to characterize the porous structure of the carbons. The electrochemical performance of the capacitors in 6 mol/L KOH was investigated with constant current charge and discharge experiments. A specific capacitance larger than 160 F/g was achieved with an electrode composed of 75% active carbon with a specific surface area of 1180 m2/g and 20% graphite as conductive agent. Evaluation of capacitor performance was conducted by different techniques, e.g. voltammetry and impedance spectroscopy. Characteristics of the capacitor were also discussed. A hybrid power source consisting of nickel- hydrogen and double layer capacitor was demonstrated by powering successfully a simulated power load encountered in communication equipment.展开更多
In contrast to the conventional etching that makes nanoparticles rounder and our previous sharpening etching mode that causes serrated edges,here,we developed a new boring etching mode that targets the faces of Au nan...In contrast to the conventional etching that makes nanoparticles rounder and our previous sharpening etching mode that causes serrated edges,here,we developed a new boring etching mode that targets the faces of Au nanoplates to make holes.The critical factors are the pre-incubation step with the ligand 2-mercapto-5-benzimidazolecarboxylic acid(MBIA)and the subsequent removal of excess ligands in the solution.Thus,etching is focused onto the few sites with initial loss of ligands,which cannot be quickly replaced.The choice of ligand MBIA is also of importance,as it carries negative charge and repels each other.Its inability of forming a dense layer probably plays a critical role in the site-selectivity for faces,because ligands at the higher curvature edges and corners are expected to have less repulsion.The etching results from the comproportionation reaction between Au3+and Au0 in the nanoplates,where Br-coordination to Au and the extra stabilization from cetyltrimethylammonium bromide(CTAB)are essential.We believe that the ability of boring holes is an important tool for future synthetic designs.展开更多
In the present study, the selection of an etchant for a particular crystal was purely made on empirical basis. The gel grown barium oxalate crystals were etched by HCl, HNO3, BaCl2, NH4Cl, and NH4Cl-HCl solutions. Mic...In the present study, the selection of an etchant for a particular crystal was purely made on empirical basis. The gel grown barium oxalate crystals were etched by HCl, HNO3, BaCl2, NH4Cl, and NH4Cl-HCl solutions. Micro-topographical studies have been made and it was found that elongated triangular etch pits and pits within pits were formed. Rectangular growth layers in the form of staircase and leaf like dendrite pattern were seen. Kinetics of etching was studied. Quantitative estimation of dissolved crystals in etchants was used for the determination of activation energy of reaction and pre-exponential factor with the help of Arrhenius equation.展开更多
A post-synthesis modification method, named ion etching, is proposed to adjust the morphology of titanium silicalite TS-1 for a better catalytic activity. The new method mainly involves treating titanium silicalite TS...A post-synthesis modification method, named ion etching, is proposed to adjust the morphology of titanium silicalite TS-1 for a better catalytic activity. The new method mainly involves treating titanium silicalite TS-1 with an ammonia-containing aqueous solution in autoclave under the conditions of ca. ammonia aqueous solution concentration 0.5-14 mol/L NH 3, volume ratio of liquid/solid 20-100, hydrothermal temperature 100-180 ℃ and contact time 24-500 h. According to the characterizations by SEM, XRF, XRD, FTIR and UV-Vis, the modification can transform a well-defined large crystal TS-1[1 μm×2 μm×6 μm, n(Si)/n(Ti)=53.62] into fine grains which can avoid falling off from the matrix if the conditions of the treatment are properly controlled. The effect of ion etching upon TS-1 morphology is attributed to the OH - ion(derives from NH 3·H 2O) catalyzed hydrolysis of the T-O-T bridge bond of the silicic zeolitic framework. Its main advantages over mechanical ball-millingthe conventional zeolitic morphology modification method, include actually fully retained crystallinity and almost intact coordination state of the active Ti sites of the remained framework, as confirmed by XRD, FTIR and UV-Vis. Probe reaction shows that, the large crystal TS-1 modified by the present method at 170 ℃ for 129 h, when used as the catalyst for epoxidation of propylene, could be operated at propylene weight hourly space velocity of 0.5 h -1, and 97.85% hydrogen peroxide conversion and 96.87% propylene oxide selectivity were obtained. However, to reach comparative hydrogen peroxide conversion, the intact zeolite could only be operated under propylene weight hourly space velocity of 0.2 h -1. The remarkable increase of the catalytic activity of the modified TS-1 may be attributed to the improved intra-crystal diffusivity and the excellent preservation of the crystallinity and active Ti sites by the present modification.展开更多
基金The authors greatly acknowledge financial support from the National Natural Science Foundation of China(No.59807001).
文摘The electrochemical storage of energy in a special kind of active carbon materials used as capacitor electrodes is considered. Petroleum coke was used for preparation of carbons with different porosities by KOH and vapor etching with catalysis of FeCI3 in turn. Carbon electrodes were fabricated and used as electrodes of double layer capacitors. Nitrogen adsorption was used to characterize the porous structure of the carbons. The electrochemical performance of the capacitors in 6 mol/L KOH was investigated with constant current charge and discharge experiments. A specific capacitance larger than 160 F/g was achieved with an electrode composed of 75% active carbon with a specific surface area of 1180 m2/g and 20% graphite as conductive agent. Evaluation of capacitor performance was conducted by different techniques, e.g. voltammetry and impedance spectroscopy. Characteristics of the capacitor were also discussed. A hybrid power source consisting of nickel- hydrogen and double layer capacitor was demonstrated by powering successfully a simulated power load encountered in communication equipment.
基金the financial support from the National Natural Science Foundation of China(Nos.91956109,92356310,and 22075137)Zhejiang Provincial Natural Science Foundation of China:Major Program(No.2022XHSJJ002)+1 种基金Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang(No.TD2022004)Foundation of Westlake University.
文摘In contrast to the conventional etching that makes nanoparticles rounder and our previous sharpening etching mode that causes serrated edges,here,we developed a new boring etching mode that targets the faces of Au nanoplates to make holes.The critical factors are the pre-incubation step with the ligand 2-mercapto-5-benzimidazolecarboxylic acid(MBIA)and the subsequent removal of excess ligands in the solution.Thus,etching is focused onto the few sites with initial loss of ligands,which cannot be quickly replaced.The choice of ligand MBIA is also of importance,as it carries negative charge and repels each other.Its inability of forming a dense layer probably plays a critical role in the site-selectivity for faces,because ligands at the higher curvature edges and corners are expected to have less repulsion.The etching results from the comproportionation reaction between Au3+and Au0 in the nanoplates,where Br-coordination to Au and the extra stabilization from cetyltrimethylammonium bromide(CTAB)are essential.We believe that the ability of boring holes is an important tool for future synthetic designs.
文摘In the present study, the selection of an etchant for a particular crystal was purely made on empirical basis. The gel grown barium oxalate crystals were etched by HCl, HNO3, BaCl2, NH4Cl, and NH4Cl-HCl solutions. Micro-topographical studies have been made and it was found that elongated triangular etch pits and pits within pits were formed. Rectangular growth layers in the form of staircase and leaf like dendrite pattern were seen. Kinetics of etching was studied. Quantitative estimation of dissolved crystals in etchants was used for the determination of activation energy of reaction and pre-exponential factor with the help of Arrhenius equation.
文摘A post-synthesis modification method, named ion etching, is proposed to adjust the morphology of titanium silicalite TS-1 for a better catalytic activity. The new method mainly involves treating titanium silicalite TS-1 with an ammonia-containing aqueous solution in autoclave under the conditions of ca. ammonia aqueous solution concentration 0.5-14 mol/L NH 3, volume ratio of liquid/solid 20-100, hydrothermal temperature 100-180 ℃ and contact time 24-500 h. According to the characterizations by SEM, XRF, XRD, FTIR and UV-Vis, the modification can transform a well-defined large crystal TS-1[1 μm×2 μm×6 μm, n(Si)/n(Ti)=53.62] into fine grains which can avoid falling off from the matrix if the conditions of the treatment are properly controlled. The effect of ion etching upon TS-1 morphology is attributed to the OH - ion(derives from NH 3·H 2O) catalyzed hydrolysis of the T-O-T bridge bond of the silicic zeolitic framework. Its main advantages over mechanical ball-millingthe conventional zeolitic morphology modification method, include actually fully retained crystallinity and almost intact coordination state of the active Ti sites of the remained framework, as confirmed by XRD, FTIR and UV-Vis. Probe reaction shows that, the large crystal TS-1 modified by the present method at 170 ℃ for 129 h, when used as the catalyst for epoxidation of propylene, could be operated at propylene weight hourly space velocity of 0.5 h -1, and 97.85% hydrogen peroxide conversion and 96.87% propylene oxide selectivity were obtained. However, to reach comparative hydrogen peroxide conversion, the intact zeolite could only be operated under propylene weight hourly space velocity of 0.2 h -1. The remarkable increase of the catalytic activity of the modified TS-1 may be attributed to the improved intra-crystal diffusivity and the excellent preservation of the crystallinity and active Ti sites by the present modification.
