Up to now, there are rare reports of CoF2 spheres used as high capacity cathode materials. Herein, porous CoF2 spheres were synthesized and studied as cathode materials for LIBs. The porous CoF2 spheres were synthesiz...Up to now, there are rare reports of CoF2 spheres used as high capacity cathode materials. Herein, porous CoF2 spheres were synthesized and studied as cathode materials for LIBs. The porous CoF2 spheres were synthesized by a facile one-pot solvothermal method using a safe and inexpensive ammonium fluoride as the fluorine sources. The nature of the synthesis can avoid using corrosive fluorine sources and additional high-temperature thermal treatment The structure, morphologies and electrochemical performance of the samples obtained at different reaction times and solvothermal temperatures were investigated. The results show that the CoF2 spheres obtained at 200 ℃ for 20 h show better electrochemical performances, including a high initial discharge capacity, good capacity retention and high Coulombic efficiency. It can deliver a high initial discharge capacity of 537.8 mAoh·g-1 and keep 127.4 mA·h.g- 1 after 30 cycles used as cathode materials for lithium-ion batteries. The good electrochemical performances may be attributed to good crystallinity, porous structure and relatively intermediate sphere size.展开更多
An electrochemically stable two-dimensional covalent organic framework,PI-COF,has been synthesized by a scalable solvothermal method.PI-COF possesses a highly crystalline structure,well-defined pores,high specific sur...An electrochemically stable two-dimensional covalent organic framework,PI-COF,has been synthesized by a scalable solvothermal method.PI-COF possesses a highly crystalline structure,well-defined pores,high specific surface area,and cluster macrostructure.Thanks to these features,PI-COF can work as electrode materials in organic supercapacitors,exhibiting a specific capacitance of 163 F/g at 0.5 A/g over a wide potential window of 0-2.5 V.Moreover,PI-COF shows excellent rate performance,which can deliver 96 F/g even at a high current density of 40 A/g.Because of the high capacitance and wide potential window,PI-COF has achieved a superior energy density of 35.7 W h/kg at a power density of 250 W/kg.Most importantly,due to the remarkable electrochemical stability,the PI-COF based device shows outstanding cycling stability with 84.1%capacitance maintained(137 F/g)after 3.0×10^4 charged/discharged cycles at 1 A/g.This work should shed light on designing new COF-based electrode materials for and other electrochemical devices.展开更多
Sodium-ion batteries(SIBs) are considered as a promising next-generation energy storage system. To achieve the large-scale application of SIBs, it is crucial to develop cost-effective anode materials with high Na-ion ...Sodium-ion batteries(SIBs) are considered as a promising next-generation energy storage system. To achieve the large-scale application of SIBs, it is crucial to develop cost-effective anode materials with high Na-ion storage capacity. Herein twodimensional(2D) conjugated covalent organic frameworks(c COFs) with N-rich phthalocyanine(Pc) units fused via benzene moieties(named MPc-2D-c COFs) were explored as the SIBs anode materials. Electrochemical tests reveal their high reversible capacities of 538 and 342 m A h g^(-1) at 50 and 1000 m A g^(-1), respectively, good rate performance, and excellent stability,comparable to the state-of-the-art anode materials of SIBs, indicating their outstanding Na-ion storage performance. Ex situ Xray photoelectron and Fourier transform infrared spectroscopies together with theoretical calculations disclose the N atoms at the pore channels and conjugated pyrrole moieties of MPc-2D-c COFs provide abundant Na-ion storage sites. This, in cooperation with the enhanced electrical conductivity owing to the 2D conjugated structure, contributes to the outstanding Na-ion storage capacity of MPc-2D-c COFs. The present result is surely helpful for developing high-performance and cost-effective COFs as electroactive materials for SIBs.展开更多
Visible light photocatalysis of covalent organic frameworks(COFs) has made significant progress in recent years. Benzotrithiophene(BTT), a planar, electron-rich building block, turns out to be foundational in assembli...Visible light photocatalysis of covalent organic frameworks(COFs) has made significant progress in recent years. Benzotrithiophene(BTT), a planar, electron-rich building block, turns out to be foundational in assembling COFs in which the fullπ-conjugation of BTT is essential to facilitate electron transfer. Herein, a sp~2 carbon-conjugated COF, namely BTT-sp~2c-COF, is assembled from benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene-2,5,8-tricarbaldehyde and [1,1′:4′,1′′-terphenyl]-4,4′′-dicarbonitrile towards photocatalysis. More importantly, TEMPO(2,2,6,6-tetramethylpiperidin-1-yl)oxyl, 1 mol%) could considerably accelerate the selective oxidation of organic sulfides with O_(2) over BTT-sp~2c-COF. TEMPO mediates hole transfer between BTT-sp~2c-COF and organic sulfides, and O-atoms are incorporated into sulfoxides via an electron transfer pathway. Merging BTT-sp~2c-COF photocatalysis with TEMPO generally applies to transforming organic sulfides into sulfoxides. This work implies the full π-conjugation of electron-rich building blocks into COFs is a viable strategy for selective visible light photocatalysis.展开更多
基金This work was supported by the Applied Fundamental Foundation of Sichuan Province （No. 2014JY0202）, the R＆D Foundation of China Academy of Engineering Physics （No. 2014B0302036）, the Science Foundation for Distinguished Young Scholars of Sichuan Province （No. 2016JQ0025） and National Natural Science Foundation of China （Nos. 21401177 and 21501160）, the ＂1000plan＂ from the Chinese Government, and the Collaborative Innovation Foundation of Sichuan University （No. XTCS2014009）.
文摘Up to now, there are rare reports of CoF2 spheres used as high capacity cathode materials. Herein, porous CoF2 spheres were synthesized and studied as cathode materials for LIBs. The porous CoF2 spheres were synthesized by a facile one-pot solvothermal method using a safe and inexpensive ammonium fluoride as the fluorine sources. The nature of the synthesis can avoid using corrosive fluorine sources and additional high-temperature thermal treatment The structure, morphologies and electrochemical performance of the samples obtained at different reaction times and solvothermal temperatures were investigated. The results show that the CoF2 spheres obtained at 200 ℃ for 20 h show better electrochemical performances, including a high initial discharge capacity, good capacity retention and high Coulombic efficiency. It can deliver a high initial discharge capacity of 537.8 mAoh·g-1 and keep 127.4 mA·h.g- 1 after 30 cycles used as cathode materials for lithium-ion batteries. The good electrochemical performances may be attributed to good crystallinity, porous structure and relatively intermediate sphere size.
基金supported by the Ministry of Science and Technology of China(No.2012CB933403)Beijing Natural Science Foundation(No.2182086)+1 种基金the National Natural Science Foundation of China(Nos.51425302 and 51302045)CAS-TWAS President's PhD Fellowship program,the Beijing Municipal Science and Technology Commission(No.Z121100006812003)the Chinese Academy of Sciences.
文摘An electrochemically stable two-dimensional covalent organic framework,PI-COF,has been synthesized by a scalable solvothermal method.PI-COF possesses a highly crystalline structure,well-defined pores,high specific surface area,and cluster macrostructure.Thanks to these features,PI-COF can work as electrode materials in organic supercapacitors,exhibiting a specific capacitance of 163 F/g at 0.5 A/g over a wide potential window of 0-2.5 V.Moreover,PI-COF shows excellent rate performance,which can deliver 96 F/g even at a high current density of 40 A/g.Because of the high capacitance and wide potential window,PI-COF has achieved a superior energy density of 35.7 W h/kg at a power density of 250 W/kg.Most importantly,due to the remarkable electrochemical stability,the PI-COF based device shows outstanding cycling stability with 84.1%capacitance maintained(137 F/g)after 3.0×10^4 charged/discharged cycles at 1 A/g.This work should shed light on designing new COF-based electrode materials for and other electrochemical devices.
基金supported by the Natural Science Foundation of China (21631003, 21871024)the Fundamental Research Funds for the Central Universities (FRF-BR-19-003B and FRF-BD-2014A)。
文摘Sodium-ion batteries(SIBs) are considered as a promising next-generation energy storage system. To achieve the large-scale application of SIBs, it is crucial to develop cost-effective anode materials with high Na-ion storage capacity. Herein twodimensional(2D) conjugated covalent organic frameworks(c COFs) with N-rich phthalocyanine(Pc) units fused via benzene moieties(named MPc-2D-c COFs) were explored as the SIBs anode materials. Electrochemical tests reveal their high reversible capacities of 538 and 342 m A h g^(-1) at 50 and 1000 m A g^(-1), respectively, good rate performance, and excellent stability,comparable to the state-of-the-art anode materials of SIBs, indicating their outstanding Na-ion storage performance. Ex situ Xray photoelectron and Fourier transform infrared spectroscopies together with theoretical calculations disclose the N atoms at the pore channels and conjugated pyrrole moieties of MPc-2D-c COFs provide abundant Na-ion storage sites. This, in cooperation with the enhanced electrical conductivity owing to the 2D conjugated structure, contributes to the outstanding Na-ion storage capacity of MPc-2D-c COFs. The present result is surely helpful for developing high-performance and cost-effective COFs as electroactive materials for SIBs.
基金supported by the National Natural Science Foundation of China (22072108)。
文摘Visible light photocatalysis of covalent organic frameworks(COFs) has made significant progress in recent years. Benzotrithiophene(BTT), a planar, electron-rich building block, turns out to be foundational in assembling COFs in which the fullπ-conjugation of BTT is essential to facilitate electron transfer. Herein, a sp~2 carbon-conjugated COF, namely BTT-sp~2c-COF, is assembled from benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene-2,5,8-tricarbaldehyde and [1,1′:4′,1′′-terphenyl]-4,4′′-dicarbonitrile towards photocatalysis. More importantly, TEMPO(2,2,6,6-tetramethylpiperidin-1-yl)oxyl, 1 mol%) could considerably accelerate the selective oxidation of organic sulfides with O_(2) over BTT-sp~2c-COF. TEMPO mediates hole transfer between BTT-sp~2c-COF and organic sulfides, and O-atoms are incorporated into sulfoxides via an electron transfer pathway. Merging BTT-sp~2c-COF photocatalysis with TEMPO generally applies to transforming organic sulfides into sulfoxides. This work implies the full π-conjugation of electron-rich building blocks into COFs is a viable strategy for selective visible light photocatalysis.
