Activated carbons(ACs) with a wide range of surface areas were made from petroleum coke by means of KOH activation. The electrochemical characterization was carried out for several activated carbons used as polarizabl...Activated carbons(ACs) with a wide range of surface areas were made from petroleum coke by means of KOH activation. The electrochemical characterization was carried out for several activated carbons used as polarizable electrodes of electric double-layer capacitors(EDLCs) in an aqueous electrolytic solution. The porous structures and electrochemical double-layer capacitance of the activated carbons were investigated by virtue of nitrogen gas adsorption and constant current cycling(CCC) methods. The relationship among the surface area, pore volume of the activated carbons and specific double-layer capacitance was discussed. It was found that the specific capacitance of ACs increased linearly with the increase of surface area. The presence of mesopores in the activated carbons with very high surface area(>2000 m\+2/g) was not very effective for them to be used as EDLCs. The influence of chemical characteristics of the activated carbons on the double layer formation could be considered to be negligible.展开更多
Graphene-based frameworks suffer from a low quantum capacitance due to graphene’s Dirac point at the Fermi level.This theoretical study investigated the effect structural defects,nitrogen and boron doping,and surface...Graphene-based frameworks suffer from a low quantum capacitance due to graphene’s Dirac point at the Fermi level.This theoretical study investigated the effect structural defects,nitrogen and boron doping,and surface epoxy/hydroxy groups have on the electronic structure and capacitance of graphene.Density functional theory calculations reveal that the lowest energy configurations for nitrogen or boron substitutional doping occur when the dopant atoms are segregated.This elucidates why the magnetic transition for nitrogen doping is experimentally only observed at higher doping levels.We also highlight that the lowest energy configuration for a single vacancy defect is magnetic.Joint density functional theory calculations show that the fixed band approximation becomes increasingly inaccurate for electrolytes with lower dielectric constants.The introduction of structural defects rather than nitrogen or boron substitutional doping,or the introduction of adatoms leads to the largest increase in density of states and capacitance around graphene’s Dirac point.However,the presence of adatoms or substitutional doping leads to a larger shift of the potential of zero charge away from graphene’s Dirac point.展开更多
In order to understand the electric interfacial behavior, mean field based electric double layer （EDL） theory has been continuously developed over the past 150 years. In this article, we briefly review the developme...In order to understand the electric interfacial behavior, mean field based electric double layer （EDL） theory has been continuously developed over the past 150 years. In this article, we briefly review the development of the EDL model, from the dimensionless Gouy-Chapman model to the symmetric Bikerman-Freise model, and finally toward size-asymmetric mean field theory models. We provide the general derivations within the framework of Helmholtz free energy of the lattice- gas model, and it can be seen that the above-mentioned models are consistent in the sense that the interconversi0n among them can be achieved by reducing the basic assumptions.展开更多
Electric double layer capacitors(EDLCs),which store free charges on the electrode surface via non-Faradaic process,balanced by the electric double layer on the electrolyte side,exhibit excellent cycle stability and hi...Electric double layer capacitors(EDLCs),which store free charges on the electrode surface via non-Faradaic process,balanced by the electric double layer on the electrolyte side,exhibit excellent cycle stability and high power density.Though EDLCs are considered as promising energy storage devices,the charges stored on the electrode surface in EDLCs are much lower than those in batteries.Ionic liquids(ILs),as a new type of electrolytes in EDLCs,are capable to deliver high energy density,due to their excellent physicochemical properties and wide electrochemical window.In this review,we focus on the widely studied IL electrolytes for EDLCs,including pure ILs,IL/IL binary electrolytes,IL/organic solvent mixtures,as well as functionalized ILs,with attention on the relationship between the structures of different IL-based electrolytes and the energy storage properties in EDLCs.For imidazolium-and ammonium-based IL electrolytes which are most widely studied in EDLCs,the former generally have higher gravimetric specific capacitance,while the latter exhibit wider electrochemical window.The modifications of functional group substituted can be an effective strategy to enhance the gravimetric specific capacitance of the latter and thus improve the energy density of EDLCs.展开更多
Polarizable electrode of electric double layer capacitor was made from carbon nanotubes. The effect of acid oxidation of electrode on the specific capacitance was studied. Oxidation removed the redundant carbon, expan...Polarizable electrode of electric double layer capacitor was made from carbon nanotubes. The effect of acid oxidation of electrode on the specific capacitance was studied. Oxidation removed the redundant carbon, expanded the pore size and introducedf some kinds of functional groups on the surface of CNTs. The specific capacitance of the electrodes winth organic electrolyte was increased from 21.4 to 49.6 F/g after being oxidized at a volume ratio H2SO4 to HNO3 of 3:1.展开更多
基金Supported by the Young Teacher Scientific Research Foundation of BU CT(No.QN0 2 4 9) and National Natural ScienceFoundation(No.5 0 2 72 0 70 )
文摘Activated carbons(ACs) with a wide range of surface areas were made from petroleum coke by means of KOH activation. The electrochemical characterization was carried out for several activated carbons used as polarizable electrodes of electric double-layer capacitors(EDLCs) in an aqueous electrolytic solution. The porous structures and electrochemical double-layer capacitance of the activated carbons were investigated by virtue of nitrogen gas adsorption and constant current cycling(CCC) methods. The relationship among the surface area, pore volume of the activated carbons and specific double-layer capacitance was discussed. It was found that the specific capacitance of ACs increased linearly with the increase of surface area. The presence of mesopores in the activated carbons with very high surface area(>2000 m\+2/g) was not very effective for them to be used as EDLCs. The influence of chemical characteristics of the activated carbons on the double layer formation could be considered to be negligible.
基金supported partially by JST SICORP(Grant No.JPMJSC2112)JST Adaptable and Seamless Technology Transfer Program through Target-driven R&D(A-STEP)(Grant No.JPMJTR22T6),and JSPS KAKENHI(Grant No.22K14757)+1 种基金Calculations were performed using the U.K.National Supercomputing Facility ARCHER2(http://www.archer2.ac.uk)via our membership of the U.K.’s HEC Materials Chemistry Consortium,which is funded by the EPSRC(Grant Nos.EP/L000202 and EP/R029431)the Molecular Modelling Hub for computational resources,MMM Hub,which is partially funded by EPSRC(Grant No.EP/P020194/1).This research has also utilized Queen Mary’s Apocrita HPC facility,supported by QMUL Research-IT.
文摘Graphene-based frameworks suffer from a low quantum capacitance due to graphene’s Dirac point at the Fermi level.This theoretical study investigated the effect structural defects,nitrogen and boron doping,and surface epoxy/hydroxy groups have on the electronic structure and capacitance of graphene.Density functional theory calculations reveal that the lowest energy configurations for nitrogen or boron substitutional doping occur when the dopant atoms are segregated.This elucidates why the magnetic transition for nitrogen doping is experimentally only observed at higher doping levels.We also highlight that the lowest energy configuration for a single vacancy defect is magnetic.Joint density functional theory calculations show that the fixed band approximation becomes increasingly inaccurate for electrolytes with lower dielectric constants.The introduction of structural defects rather than nitrogen or boron substitutional doping,or the introduction of adatoms leads to the largest increase in density of states and capacitance around graphene’s Dirac point.However,the presence of adatoms or substitutional doping leads to a larger shift of the potential of zero charge away from graphene’s Dirac point.
基金supported by the National Natural Science Foundation of China(Grant Nos.21421001,21373118,and 21203100)the Natural Science Foundation of Tianjin,China(Grant No.13JCQNJC06700)+1 种基金the MOE Innovation Team of China(Grant No.IRT13022)NFFTBS(Grant No.J1103306)
文摘In order to understand the electric interfacial behavior, mean field based electric double layer （EDL） theory has been continuously developed over the past 150 years. In this article, we briefly review the development of the EDL model, from the dimensionless Gouy-Chapman model to the symmetric Bikerman-Freise model, and finally toward size-asymmetric mean field theory models. We provide the general derivations within the framework of Helmholtz free energy of the lattice- gas model, and it can be seen that the above-mentioned models are consistent in the sense that the interconversi0n among them can be achieved by reducing the basic assumptions.
基金supported by the National Natural Science Foundation of China (21373118, 21573112, 21421001 and 21703108)
文摘Electric double layer capacitors(EDLCs),which store free charges on the electrode surface via non-Faradaic process,balanced by the electric double layer on the electrolyte side,exhibit excellent cycle stability and high power density.Though EDLCs are considered as promising energy storage devices,the charges stored on the electrode surface in EDLCs are much lower than those in batteries.Ionic liquids(ILs),as a new type of electrolytes in EDLCs,are capable to deliver high energy density,due to their excellent physicochemical properties and wide electrochemical window.In this review,we focus on the widely studied IL electrolytes for EDLCs,including pure ILs,IL/IL binary electrolytes,IL/organic solvent mixtures,as well as functionalized ILs,with attention on the relationship between the structures of different IL-based electrolytes and the energy storage properties in EDLCs.For imidazolium-and ammonium-based IL electrolytes which are most widely studied in EDLCs,the former generally have higher gravimetric specific capacitance,while the latter exhibit wider electrochemical window.The modifications of functional group substituted can be an effective strategy to enhance the gravimetric specific capacitance of the latter and thus improve the energy density of EDLCs.
文摘Polarizable electrode of electric double layer capacitor was made from carbon nanotubes. The effect of acid oxidation of electrode on the specific capacitance was studied. Oxidation removed the redundant carbon, expanded the pore size and introducedf some kinds of functional groups on the surface of CNTs. The specific capacitance of the electrodes winth organic electrolyte was increased from 21.4 to 49.6 F/g after being oxidized at a volume ratio H2SO4 to HNO3 of 3:1.
基金This work was supported by the National Natural Science Foundation of China （Nos. 50672025, 50730003）, The research fund for the Doctoral Program of Higher Education （No. 20070251008）.
