Electrochemical impedance spectroscopy(EIS)is a widely used technique to monitor the electrical properties of a catalyst under electrocatalytic conditions.Although it is extensively used for research in electrocatalys...Electrochemical impedance spectroscopy(EIS)is a widely used technique to monitor the electrical properties of a catalyst under electrocatalytic conditions.Although it is extensively used for research in electrocatalysis,its effectiveness and power have not been fully harnessed to elucidate complex interfacial processes.Herein,we use the frequency dispersion parameter,n,which is extracted from EIS measurements(C_(s)=af^(n+1),-2<n<-1),to describe the dispersion characteristics of capacitance and interfacial properties of Co_(3)O_(4) before the onset of oxygen evolution reaction(OER)in alkaline conditions.We first prove that the n-value is sensitive to the interfacial electronic changes associated with Co redox processes and surface reconstruction.The n-value decreases by increasing the specific/active surface area of the catalysts.We further modify the interfacial properties by changing different components,i.e.,replacing the proton with deuterium,adding ethanol as a new oxidant,and changing the cation in the electrolyte.Intriguingly,the n-value can identify different influences on the interfacial process of proton transfer,the decrease and blocking of oxidized Co species,and the interfacial water structure.We demonstrate that the n-value extracted from EIS measurements is sensitive to the kinetic isotope effect,electrolyte cation,adsorbate surface coverage of oxidized Co species,and the interfacial water structure.Thus,it can be helpful to differentiate the multiple factors affecting the catalyst interface.These findings convey that the frequency dispersion of capacitance is a convenient and useful method to uncover the interfacial properties under electrocatalytic conditions,which helps to advance the understanding of the interfaceactivity relationship.展开更多
The development of high-performance,reproducible carbon(C)-based supercapacitors remains a significant challenge because of limited specific capacitance.Herein,we present a novel strategy for fabricating LaCoO_(x) and...The development of high-performance,reproducible carbon(C)-based supercapacitors remains a significant challenge because of limited specific capacitance.Herein,we present a novel strategy for fabricating LaCoO_(x) and cobalt(Co)-doped nanoporous C(LaCoO_(x)/Co@ZNC)through the carbonization of Co/Zn-zeolitic imidazolate framework(ZIF)crystals derived from a PVP-Co/Zn/La precursor.The unique ZIF structure effectively disrupted the graphitic C framework,preserved the Co active sites,and enhanced the electrical conductivity.The synergistic interaction between pyridinic nitrogen and Co ions further promoted redox reactions.In addition,the formation of a hierarchical pore structure through zinc sublimation facili-tated electrolyte diffusion.The resulting LaCoO_(x)/Co@ZNC exhibited exceptional electrochemical performance,delivering a remarkable specific capacitance of 2,789 F/g at 1 A/g and outstanding cycling stability with 92%capacitance retention after 3,750 cycles.Our findings provide the basis for a promising approach to advancing C-based energy storage technologies.展开更多
Transient negative capacitance(NC),as an available dynamic charge effect achieved in resistor-ferroelectric capacitor(R-FEC)circuits,has triggered a series of theoretical and experimental works focusing on its physica...Transient negative capacitance(NC),as an available dynamic charge effect achieved in resistor-ferroelectric capacitor(R-FEC)circuits,has triggered a series of theoretical and experimental works focusing on its physical mechanism and device application.Here,we analytically derived the effects of different mechanical conditions on the transient NC behaviors in the R-FEC circuit based on the phenomenological model.It shows that the ferroelectric capacitor can exhibit either NC(i.e.,“single NC”and“double NC”)or positive capacitance,depending on the mechanical condition and temperature.Further numerical calculations show that the voltage drop caused by NC can be effectively controlled by temperature,applied stress,or strain.The relationship between NC voltage drop and system configurations including external resistance,dynamical coefficient of polarization,and input voltage are presented,showing diverse strategies to manipulate the NC effect.These results provide theoretical guidelines for rational design and efficient control of NC-related electronic devices.展开更多
Vanadium nitride(VN)is a promising pseudocapacitive material due to the high theoretical capacity,rapid redox Faradaic kinetics,and appropriate potential window.Although VN shows large pseudocapacitance in alkaline el...Vanadium nitride(VN)is a promising pseudocapacitive material due to the high theoretical capacity,rapid redox Faradaic kinetics,and appropriate potential window.Although VN shows large pseudocapacitance in alkaline electrolytes,the electrochemical instability and capacity degradation of VN electrode materials present significant challenges for practical applications.Herein,the capacitance decay mechanism of VN is investigated and a simple strategy to improve cycling stability of VN supercapacitor electrodes is proposed by introducing VO_(4)^(3-)anion in KOH electrolytes.Our results show that the VN electrode is electrochemical stabilization between-1.0and-0.4 V(vs.Hg/Hg O reference electrode)in 1.0 MKOH electrolyte,but demonstrates irreversible oxidation and fast capacitance decay in the potential range of-0.4 to0 V.In situ electrochemical measurements reveal that the capacitance decay of VN from-0.4 to 0 V is ascribed to the irreversible oxidation of vanadium(V)of N–V–O species by oxygen(O)of OH^(-).The as-generated oxidization species are subsequently dissolved into KOH electrolytes,thereby undermining the electrochemical stability of VN.However,this irreversible oxidation process could be hindered by introducing VO_(4)^(3-)in KOH electrolytes.A high volumetric specific capacitance of671.9 F.cm^(-3)(1 A.cm^(-3))and excellent cycling stability(120.3%over 1000 cycles)are achieved for VN nanorod electrode in KOH electrolytes containing VO_(4)^(3-).This study not only elucidates the failure mechanism of VN supercapacitor electrodes in alkaline electrolytes,but also provides new insights into enhancing pseudocapacitive energy storage of VN-based electrode materials.展开更多
Noise is inevitable in electrical capacitance tomography(ECT)measurements.This paper describes the influence of noise on ECT performance for measuring gas-solids fluidized bed characteristics.The noise distribution is...Noise is inevitable in electrical capacitance tomography(ECT)measurements.This paper describes the influence of noise on ECT performance for measuring gas-solids fluidized bed characteristics.The noise distribution is approximated by the Gaussian distribution and added to experimental capacitance data with various intensities.The equivalent signal strength(Ф)that equals the signal-to-noise ratio of packed beds is used to evaluate noise levels.Results show that the Pearson correlation coefficient,which indicates the similarity of solids fraction distributions over pixels,increases with Ф,and reconstructed images are more deteriorated at lower Ф.Nevertheless,relative errors for average solids fraction and bubble size in each frame are less sensitive to noise,attributed to noise compromise caused by the process of pixel values.These findings provide useful guidance for assessing the accuracy of ECT measurements of multiphase flows.展开更多
During oilfield development,a comprehensive model for assessing inter-well connectivity and connected volume within reservoirs is crucial.Traditional capacitance(TC)models,widely used in inter-well data analysis,face ...During oilfield development,a comprehensive model for assessing inter-well connectivity and connected volume within reservoirs is crucial.Traditional capacitance(TC)models,widely used in inter-well data analysis,face challenges when dealing with rapidly changing reservoir conditions over time.Additionally,TC models struggle with complex,random noise primarily caused by measurement errors in production and injection rates.To address these challenges,this study introduces a dynamic capacitance(SV-DC)model based on state variables.By integrating the extended Kalman filter(EKF)algorithm,the SV-DC model provides more flexible predictions of inter-well connectivity and time-lag efficiency compared to the TC model.The robustness of the SV-DC model is verified by comparing relative errors between preset and calculated values through Monte Carlo simulations.Sensitivity analysis was performed to compare the model performance with the benchmark,using the Qinhuangdao Oilfield as a case study.The results show that the SV-DC model accurately predicts water breakthrough times.Increases in the liquid production index and water cut in two typical wells indicate the development time of ineffective circulation channels,further confirming the accuracy and reliability of the model.The SV-DC model offers significant advantages in addressing complex,dynamic oilfield production scenarios and serves as a valuable tool for the efficient and precise planning and management of future oilfield developments.展开更多
Zn-ion hybrid supercapacitors(ZHSCs),as emerging energy storage systems,combine high energy and power density with cost-effectiveness and safety,attracting significant attention.However,due to the inherent energy stor...Zn-ion hybrid supercapacitors(ZHSCs),as emerging energy storage systems,combine high energy and power density with cost-effectiveness and safety,attracting significant attention.However,due to the inherent energy storage mechanism and the diminishing marginal benefits of increased porosity on capacitance,engineering porous nanostructures to develop carbon materials with ideal architectures is crucial for achieving high performance.Herein,a novel web-in-web porous carbon/carbon nanotubes(CNTs)composite has been proposed,fabricated by a simple phase separation method and two-step carbonization.During pre-oxidation,gradual air oxidation induces the formation of an O,N co-doped polymer-chain template,which subsequently transforms into a graphitized web during high-temperature carbonization.The optimized web-in-web structure,enriched with abundant active sites,accelerates mass transport and charge transfer kinetics.When assembled in ZHSCs,the web-in-web cathode achieved a high area capacitance(14,309 mF cm^(-2))with high mass loading(38.2 mg cm^(-2)).It delivered excellent high-rate performance at 50 mA cm^(-2)with a capacitance retention of 83%after 10,000 cycles,also boosting a high energy density(1452.7μWh cm^(-2))and power density(30.8 mW cm^(-2)).Furthermore,ex situ characterization and in situ electrochemical analyses reveal hybrid energy storage mechanisms,involving both physical/chemical adsorption and precipitation/dissolution across different potential regions.This study provides a promising strategy for designing high-area-capacitance carbon cathodes boosting high-performance ZHSCs.展开更多
Neodymium chromium oxide(NdCrO_(3))and NdCrO_(3)/graphene oxide(GO)nanocomposite were synthesized via sol-gel and co-precipitation techniques for being used in high-perfo rmance supercapacitors and for the possible ap...Neodymium chromium oxide(NdCrO_(3))and NdCrO_(3)/graphene oxide(GO)nanocomposite were synthesized via sol-gel and co-precipitation techniques for being used in high-perfo rmance supercapacitors and for the possible application in ultraviolet(UV)materials.Herein the systematic synthesis approach was adopted,which enhances the optical and electrical properties of the grown wide band-gap composite nanomaterial.Structural characterization of the grown materials was attempted using X-ray diffraction(XRD)and scanning electron microscopy(SEM).Most importantly the electrochemical analysis of the grown samples was carried out by employing a glassy carbon electrode and 3 mol/L KOH electrolyte,which demonstrates significant improvements in a specific capacitance of approximately360 F/g,an energy density of approximately 18 Wh/kg,and a maximum power density of approximately 257 W/kg,respectively.Moreover,NdCrO_(3)/GO nanocomposite maintains a cyclic stability of 97.6%after4000 cycles.Photoluminescence(PL)spectroscopy confirms the wide bandgap nature of the NdCrO_(3)and NdCrO_(3)/GO nanocomposite,indicating its potential application in UVC devices.These findings emphasize the potential of the NdCrO_(3)/GO nanocomposite in advancing efficient energy storage solutions and the possibility of being used in UVC technology.展开更多
The negative ion based neutral beam injector(NNBI)with a beam energy of 400 keV is one of the subsystems at the Comprehensive Research fAcility for Fusion Technology(CRAFT)in China.The distributed capacitance of the h...The negative ion based neutral beam injector(NNBI)with a beam energy of 400 keV is one of the subsystems at the Comprehensive Research fAcility for Fusion Technology(CRAFT)in China.The distributed capacitance of the high-voltage components is an important basis for the design of surge suppression devices at CRAFT NNBI.This study conducted calculations of distributed capacitance for the key components,including the high-voltage deck,transmission line and isolation transformer in the power supply system using the finite element method.The relationship between the high-voltage deck(HVD)distributed capacitance and the distance from the wall is discussed.The differences in distributed capacitance and energy storage between noncoaxial and coaxial transmission lines are also debated.Finally,the capacitance between the primary and secondary windings of the-400 kV isolation transformer,as well as between the secondary winding and the oil tank casing,was calculated.展开更多
A distributed capacitance model for monolithic inductors is developed to predict the equivalently parasitical capacitances of the inductor.The ratio of the self-resonant frequency (f SR) of the differential-driven sym...A distributed capacitance model for monolithic inductors is developed to predict the equivalently parasitical capacitances of the inductor.The ratio of the self-resonant frequency (f SR) of the differential-driven symmetric inductor to the f SR of the single-ended driven inductor is firstly predicted and explained.Compared with a single-ended configuration,experimental data demonstrate that the differential inductor offers a 127% greater maximum quality factor and a broader range of operating frequencies.Two differential inductors with low parasitical capacitance are developed and validated.展开更多
In view of drastic possible changes in fuze environment tempera- ture,a kind of temperature autocompensated detecting circuit for the capaci- tance fuze is proposed.It provides a steady detected output when the envi- ...In view of drastic possible changes in fuze environment tempera- ture,a kind of temperature autocompensated detecting circuit for the capaci- tance fuze is proposed.It provides a steady detected output when the envi- ronment temperature varies from-50℃ to 65℃ and keeps a stable detecting sensitivity.Based on an analysis of the circuit,influence of the major param- eters of the oscillating circuit on the amplitude are explored.A few impor- tant controllable parameters affecting the circuit feature are found out.A parameter-control method is given in order to improve the circuit perfor- mance.展开更多
For establishing the equation of the capacitive target detection accurately, the distributing characteristics of the charges on the bomb body with capacitance fuze were explored. Continuous charges were analyzed disp...For establishing the equation of the capacitive target detection accurately, the distributing characteristics of the charges on the bomb body with capacitance fuze were explored. Continuous charges were analyzed dispersively. Based on the Coulomb's law, the dynamic equilibrium equations of the inducing charges on the bomb body were set up. For the four cases of d 0/L (the ratio between the electrode distance and the bomb length), the curves of the charge's distribution were given. It was concluded that: ① the charge density decreases steadily from the end near the frontal electrode to the bomb tail; ② the declining rate of the density is governed by d 0/L , the larger the value of d 0/L ,the higher the declining rate, and vice versa.展开更多
For a detector in a capacitanee fuze working in an electrostatic field, the bomblength (effective length of the conductor part) is an important factor affecting the sensitivityof detection. For the two different kinds...For a detector in a capacitanee fuze working in an electrostatic field, the bomblength (effective length of the conductor part) is an important factor affecting the sensitivityof detection. For the two different kinds of detecting circuit models in general use (the frequency-sensitive and the amplitude-coupling ), mechanism of the effect of bomblength on the sensitvity of detection is analyzed. Through the analysis a conclusion in fullagreement with experimental results has been drawn, that is. the longer the bomb length,the higher the sensitivity, on the condition that the sizes and the sites of the detecting electrodes and bomb diameter remain unchanged.展开更多
The finite element method is first introduced into the design process of detecting electrodes of three electrode capacitance fuze, the mutual capacitance of the fuze and target is calculated by the finite element met...The finite element method is first introduced into the design process of detecting electrodes of three electrode capacitance fuze, the mutual capacitance of the fuze and target is calculated by the finite element method, which provides the parameters for simulation circuit and design of detecting electrode. The finite element method pierces the traditional method of designing detecting electrode-design, test and adjustment. The system capacitance can be calculated accurately and the performance can be predicted in the design period of the detecting electrode, which saves a lot of research fee. The capacitances of a mortar shell fuze above ground 2 m and lower are given. After putting the computing data into simulating circuit, the demodulation voltage can be obtained, its changing trend is in agreement with the tested result.展开更多
A nanocomposite of nickel oxide/carbon nanotubes was prepared through a simple chemical precipitation followed by thermal annealing. The electrochemical capacitance of this electrode material was studied. When the mas...A nanocomposite of nickel oxide/carbon nanotubes was prepared through a simple chemical precipitation followed by thermal annealing. The electrochemical capacitance of this electrode material was studied. When the mass fraction of CNTs (carbon nanotubes) in NiO/CNT composites increases, the electrical resistivity of nanocomposites decreases and becomes similar to that of pure CNTs when it reaches 30%. The specific surface area of composites increases with increasing CNT mass fraction and the specific capacitance reaches 160 F/g under 10 mA/g discharge current density at CNT mass fraction of 10%.展开更多
Periodic arrays of negative capacitance shunted piezoelectric patches are employed to control the band gaps of phononic beams. The location and the extent of induced band gap depend on the mismatch in impedance genera...Periodic arrays of negative capacitance shunted piezoelectric patches are employed to control the band gaps of phononic beams. The location and the extent of induced band gap depend on the mismatch in impedance generated by each patch. The total impedance mismatch is determined by the added mass and stiffness of each patch as well as the shunting electrical impedance. Therefore, the band gap of the shunted phononic beam can be actively tuned by appropriately selecting the value of negative capacitance. The control of the band gap of phononic beam with negative capacitive shunt is demonstrated numerically by employing transfer matrix method. The result reveals that using negative capacitive shunt to tune the band gap is effective.展开更多
The morphology of etched aluminum foil was observed using scanning electron microscopy, which led to the establishment of a cylindrical model and two merged models, considering the fixed weight loss of etching. The ma...The morphology of etched aluminum foil was observed using scanning electron microscopy, which led to the establishment of a cylindrical model and two merged models, considering the fixed weight loss of etching. The maximum of specific capacitance and the cor- responding optimum values for tunnel sizes at various anodization voltages were predicted. The increased size distribution and taper of tun- nels were demonstrated to decrease the specific capacitance, whereas the addition of polymeric additive into the ttmnel widening solution was demonstrated to increase the capacitance. The formation of merged tunnels on the etched aluminum surface, irrespective of the presence of row-merged tunnels or cluster-merged tunnels, resulted in a dramatic decrease in the specific capacitance. It is concluded that, enhancing the uniformity of turmel size and distribution and avoiding the formation of merged tunnels are the effective approach to achieving the higher capacitance for the tunnel etched and formed aluminum foil.展开更多
Here we report a strategy to enhance the energy density of supercapacitors by increasing the utilization rate of the specific surface area(SSA)via wettability improvement. The nonporous gold(NPG) film is used as the e...Here we report a strategy to enhance the energy density of supercapacitors by increasing the utilization rate of the specific surface area(SSA)via wettability improvement. The nonporous gold(NPG) film is used as the electrodes and the ionic liquid [EMIM]BF4 is the electrolyte. When the electrode is coated by paraffin, an increase of the contact angle leads to a remarkable reduction of the specific capacitance. While when acetonitrile is added into the electrolyte, the contact angle is decreased and the utilization rate of SSA is improved, which results in an increase of the specific capacitance. The addition of isopropyl acetate into the electrolyte leads to a further increase of the specific capacitance. To generalize the role of the wettability in improving the energy density, a carbon-based electrode is evaluated in the solution of potassium hydroxide. An addition of propyl alcohol into the potassium hydroxide solution leads to an increase of the specific capacitance, as well as a long-term stability of the supercapacitor. The role of conductivity in this study is excluded by designing experiments. This paper highlights the significance of wettability in determining the specific capacitance, showing an alternative to improve the energy density of supercapacitors.展开更多
基金Swiss National Science Foundation through its PRIM A grant(grant No.PR00P2_193111)the NCCR MARVEL,a National Centre of Competence in Researchfunded by the Swiss National Science Foundation。
文摘Electrochemical impedance spectroscopy(EIS)is a widely used technique to monitor the electrical properties of a catalyst under electrocatalytic conditions.Although it is extensively used for research in electrocatalysis,its effectiveness and power have not been fully harnessed to elucidate complex interfacial processes.Herein,we use the frequency dispersion parameter,n,which is extracted from EIS measurements(C_(s)=af^(n+1),-2<n<-1),to describe the dispersion characteristics of capacitance and interfacial properties of Co_(3)O_(4) before the onset of oxygen evolution reaction(OER)in alkaline conditions.We first prove that the n-value is sensitive to the interfacial electronic changes associated with Co redox processes and surface reconstruction.The n-value decreases by increasing the specific/active surface area of the catalysts.We further modify the interfacial properties by changing different components,i.e.,replacing the proton with deuterium,adding ethanol as a new oxidant,and changing the cation in the electrolyte.Intriguingly,the n-value can identify different influences on the interfacial process of proton transfer,the decrease and blocking of oxidized Co species,and the interfacial water structure.We demonstrate that the n-value extracted from EIS measurements is sensitive to the kinetic isotope effect,electrolyte cation,adsorbate surface coverage of oxidized Co species,and the interfacial water structure.Thus,it can be helpful to differentiate the multiple factors affecting the catalyst interface.These findings convey that the frequency dispersion of capacitance is a convenient and useful method to uncover the interfacial properties under electrocatalytic conditions,which helps to advance the understanding of the interfaceactivity relationship.
基金supported financially by National Natural Science Foundation of China(NSFC)(Nos.22478115,22075083)the Programme of Introducing Talents of Discipline to Universities(No.B16017).
文摘The development of high-performance,reproducible carbon(C)-based supercapacitors remains a significant challenge because of limited specific capacitance.Herein,we present a novel strategy for fabricating LaCoO_(x) and cobalt(Co)-doped nanoporous C(LaCoO_(x)/Co@ZNC)through the carbonization of Co/Zn-zeolitic imidazolate framework(ZIF)crystals derived from a PVP-Co/Zn/La precursor.The unique ZIF structure effectively disrupted the graphitic C framework,preserved the Co active sites,and enhanced the electrical conductivity.The synergistic interaction between pyridinic nitrogen and Co ions further promoted redox reactions.In addition,the formation of a hierarchical pore structure through zinc sublimation facili-tated electrolyte diffusion.The resulting LaCoO_(x)/Co@ZNC exhibited exceptional electrochemical performance,delivering a remarkable specific capacitance of 2,789 F/g at 1 A/g and outstanding cycling stability with 92%capacitance retention after 3,750 cycles.Our findings provide the basis for a promising approach to advancing C-based energy storage technologies.
基金This work was supported by the National Natural Science Foundation of China(Grants Nos.12222214,12132020,12002400,and 12172386)by Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices(Grant No.2022B1212010008)+1 种基金by the National Natural Science Foundation of Guangdong Province(Grant No.2021B1515020021)by the Shenzhen Science and Techonlogy Program(Grant Nos.202206193000001 and 20220818181805001).
文摘Transient negative capacitance(NC),as an available dynamic charge effect achieved in resistor-ferroelectric capacitor(R-FEC)circuits,has triggered a series of theoretical and experimental works focusing on its physical mechanism and device application.Here,we analytically derived the effects of different mechanical conditions on the transient NC behaviors in the R-FEC circuit based on the phenomenological model.It shows that the ferroelectric capacitor can exhibit either NC(i.e.,“single NC”and“double NC”)or positive capacitance,depending on the mechanical condition and temperature.Further numerical calculations show that the voltage drop caused by NC can be effectively controlled by temperature,applied stress,or strain.The relationship between NC voltage drop and system configurations including external resistance,dynamical coefficient of polarization,and input voltage are presented,showing diverse strategies to manipulate the NC effect.These results provide theoretical guidelines for rational design and efficient control of NC-related electronic devices.
基金financially supported by the National Natural Science Foundation of China(No.U2004210)Application Foundation Frontier Project of Wuhan Science and Technology Program(No.2020010601012199)City University of Hong Kong Strategic Research Grant,Hong Kong,China(No.7005505)。
文摘Vanadium nitride(VN)is a promising pseudocapacitive material due to the high theoretical capacity,rapid redox Faradaic kinetics,and appropriate potential window.Although VN shows large pseudocapacitance in alkaline electrolytes,the electrochemical instability and capacity degradation of VN electrode materials present significant challenges for practical applications.Herein,the capacitance decay mechanism of VN is investigated and a simple strategy to improve cycling stability of VN supercapacitor electrodes is proposed by introducing VO_(4)^(3-)anion in KOH electrolytes.Our results show that the VN electrode is electrochemical stabilization between-1.0and-0.4 V(vs.Hg/Hg O reference electrode)in 1.0 MKOH electrolyte,but demonstrates irreversible oxidation and fast capacitance decay in the potential range of-0.4 to0 V.In situ electrochemical measurements reveal that the capacitance decay of VN from-0.4 to 0 V is ascribed to the irreversible oxidation of vanadium(V)of N–V–O species by oxygen(O)of OH^(-).The as-generated oxidization species are subsequently dissolved into KOH electrolytes,thereby undermining the electrochemical stability of VN.However,this irreversible oxidation process could be hindered by introducing VO_(4)^(3-)in KOH electrolytes.A high volumetric specific capacitance of671.9 F.cm^(-3)(1 A.cm^(-3))and excellent cycling stability(120.3%over 1000 cycles)are achieved for VN nanorod electrode in KOH electrolytes containing VO_(4)^(3-).This study not only elucidates the failure mechanism of VN supercapacitor electrodes in alkaline electrolytes,but also provides new insights into enhancing pseudocapacitive energy storage of VN-based electrode materials.
基金National Key Research and Development Program of China(2021YFA1501302)the National Natural Science Foundation of China(22121004,22122808)+1 种基金the Haihe Laboratory of Sustainable Chemical Transformations and the Program of Introducing Talents of Discipline to Universities(BP0618007)for financial supportsupported by the XPLORER PRIZE.
文摘Noise is inevitable in electrical capacitance tomography(ECT)measurements.This paper describes the influence of noise on ECT performance for measuring gas-solids fluidized bed characteristics.The noise distribution is approximated by the Gaussian distribution and added to experimental capacitance data with various intensities.The equivalent signal strength(Ф)that equals the signal-to-noise ratio of packed beds is used to evaluate noise levels.Results show that the Pearson correlation coefficient,which indicates the similarity of solids fraction distributions over pixels,increases with Ф,and reconstructed images are more deteriorated at lower Ф.Nevertheless,relative errors for average solids fraction and bubble size in each frame are less sensitive to noise,attributed to noise compromise caused by the process of pixel values.These findings provide useful guidance for assessing the accuracy of ECT measurements of multiphase flows.
基金the National Natural Science Foundation of China(Grant No.52374051)the Joint Fund for Enterprise Innovation and Development of NSFC(Grant No.U24B2037).
文摘During oilfield development,a comprehensive model for assessing inter-well connectivity and connected volume within reservoirs is crucial.Traditional capacitance(TC)models,widely used in inter-well data analysis,face challenges when dealing with rapidly changing reservoir conditions over time.Additionally,TC models struggle with complex,random noise primarily caused by measurement errors in production and injection rates.To address these challenges,this study introduces a dynamic capacitance(SV-DC)model based on state variables.By integrating the extended Kalman filter(EKF)algorithm,the SV-DC model provides more flexible predictions of inter-well connectivity and time-lag efficiency compared to the TC model.The robustness of the SV-DC model is verified by comparing relative errors between preset and calculated values through Monte Carlo simulations.Sensitivity analysis was performed to compare the model performance with the benchmark,using the Qinhuangdao Oilfield as a case study.The results show that the SV-DC model accurately predicts water breakthrough times.Increases in the liquid production index and water cut in two typical wells indicate the development time of ineffective circulation channels,further confirming the accuracy and reliability of the model.The SV-DC model offers significant advantages in addressing complex,dynamic oilfield production scenarios and serves as a valuable tool for the efficient and precise planning and management of future oilfield developments.
基金financially supported by the National Key Research and Development Program of China(No.2024YFA1210602)Guangdong Basic and Applied Basic Research Foundation(No.2023A1515140044)
文摘Zn-ion hybrid supercapacitors(ZHSCs),as emerging energy storage systems,combine high energy and power density with cost-effectiveness and safety,attracting significant attention.However,due to the inherent energy storage mechanism and the diminishing marginal benefits of increased porosity on capacitance,engineering porous nanostructures to develop carbon materials with ideal architectures is crucial for achieving high performance.Herein,a novel web-in-web porous carbon/carbon nanotubes(CNTs)composite has been proposed,fabricated by a simple phase separation method and two-step carbonization.During pre-oxidation,gradual air oxidation induces the formation of an O,N co-doped polymer-chain template,which subsequently transforms into a graphitized web during high-temperature carbonization.The optimized web-in-web structure,enriched with abundant active sites,accelerates mass transport and charge transfer kinetics.When assembled in ZHSCs,the web-in-web cathode achieved a high area capacitance(14,309 mF cm^(-2))with high mass loading(38.2 mg cm^(-2)).It delivered excellent high-rate performance at 50 mA cm^(-2)with a capacitance retention of 83%after 10,000 cycles,also boosting a high energy density(1452.7μWh cm^(-2))and power density(30.8 mW cm^(-2)).Furthermore,ex situ characterization and in situ electrochemical analyses reveal hybrid energy storage mechanisms,involving both physical/chemical adsorption and precipitation/dissolution across different potential regions.This study provides a promising strategy for designing high-area-capacitance carbon cathodes boosting high-performance ZHSCs.
基金support from the Deanship of Scientific Research at King Khalid University,Saudi Arabia(RGP2/505/45)。
文摘Neodymium chromium oxide(NdCrO_(3))and NdCrO_(3)/graphene oxide(GO)nanocomposite were synthesized via sol-gel and co-precipitation techniques for being used in high-perfo rmance supercapacitors and for the possible application in ultraviolet(UV)materials.Herein the systematic synthesis approach was adopted,which enhances the optical and electrical properties of the grown wide band-gap composite nanomaterial.Structural characterization of the grown materials was attempted using X-ray diffraction(XRD)and scanning electron microscopy(SEM).Most importantly the electrochemical analysis of the grown samples was carried out by employing a glassy carbon electrode and 3 mol/L KOH electrolyte,which demonstrates significant improvements in a specific capacitance of approximately360 F/g,an energy density of approximately 18 Wh/kg,and a maximum power density of approximately 257 W/kg,respectively.Moreover,NdCrO_(3)/GO nanocomposite maintains a cyclic stability of 97.6%after4000 cycles.Photoluminescence(PL)spectroscopy confirms the wide bandgap nature of the NdCrO_(3)and NdCrO_(3)/GO nanocomposite,indicating its potential application in UVC devices.These findings emphasize the potential of the NdCrO_(3)/GO nanocomposite in advancing efficient energy storage solutions and the possibility of being used in UVC technology.
基金supported by the Comprehensive Research Facility for Fusion Technology Program of China(No.2018000052-73-01-001228)National Natural Science Foundation of China(No.11975263)Postgraduate Research and Practice Innovation Program of NUAA(No.xcxjh20231501)。
文摘The negative ion based neutral beam injector(NNBI)with a beam energy of 400 keV is one of the subsystems at the Comprehensive Research fAcility for Fusion Technology(CRAFT)in China.The distributed capacitance of the high-voltage components is an important basis for the design of surge suppression devices at CRAFT NNBI.This study conducted calculations of distributed capacitance for the key components,including the high-voltage deck,transmission line and isolation transformer in the power supply system using the finite element method.The relationship between the high-voltage deck(HVD)distributed capacitance and the distance from the wall is discussed.The differences in distributed capacitance and energy storage between noncoaxial and coaxial transmission lines are also debated.Finally,the capacitance between the primary and secondary windings of the-400 kV isolation transformer,as well as between the secondary winding and the oil tank casing,was calculated.
文摘A distributed capacitance model for monolithic inductors is developed to predict the equivalently parasitical capacitances of the inductor.The ratio of the self-resonant frequency (f SR) of the differential-driven symmetric inductor to the f SR of the single-ended driven inductor is firstly predicted and explained.Compared with a single-ended configuration,experimental data demonstrate that the differential inductor offers a 127% greater maximum quality factor and a broader range of operating frequencies.Two differential inductors with low parasitical capacitance are developed and validated.
文摘In view of drastic possible changes in fuze environment tempera- ture,a kind of temperature autocompensated detecting circuit for the capaci- tance fuze is proposed.It provides a steady detected output when the envi- ronment temperature varies from-50℃ to 65℃ and keeps a stable detecting sensitivity.Based on an analysis of the circuit,influence of the major param- eters of the oscillating circuit on the amplitude are explored.A few impor- tant controllable parameters affecting the circuit feature are found out.A parameter-control method is given in order to improve the circuit perfor- mance.
文摘For establishing the equation of the capacitive target detection accurately, the distributing characteristics of the charges on the bomb body with capacitance fuze were explored. Continuous charges were analyzed dispersively. Based on the Coulomb's law, the dynamic equilibrium equations of the inducing charges on the bomb body were set up. For the four cases of d 0/L (the ratio between the electrode distance and the bomb length), the curves of the charge's distribution were given. It was concluded that: ① the charge density decreases steadily from the end near the frontal electrode to the bomb tail; ② the declining rate of the density is governed by d 0/L , the larger the value of d 0/L ,the higher the declining rate, and vice versa.
文摘For a detector in a capacitanee fuze working in an electrostatic field, the bomblength (effective length of the conductor part) is an important factor affecting the sensitivityof detection. For the two different kinds of detecting circuit models in general use (the frequency-sensitive and the amplitude-coupling ), mechanism of the effect of bomblength on the sensitvity of detection is analyzed. Through the analysis a conclusion in fullagreement with experimental results has been drawn, that is. the longer the bomb length,the higher the sensitivity, on the condition that the sizes and the sites of the detecting electrodes and bomb diameter remain unchanged.
文摘The finite element method is first introduced into the design process of detecting electrodes of three electrode capacitance fuze, the mutual capacitance of the fuze and target is calculated by the finite element method, which provides the parameters for simulation circuit and design of detecting electrode. The finite element method pierces the traditional method of designing detecting electrode-design, test and adjustment. The system capacitance can be calculated accurately and the performance can be predicted in the design period of the detecting electrode, which saves a lot of research fee. The capacitances of a mortar shell fuze above ground 2 m and lower are given. After putting the computing data into simulating circuit, the demodulation voltage can be obtained, its changing trend is in agreement with the tested result.
基金This project was financially supported by the National Natural Science Foundation of China under grant No.50307009the Ministry of Science and Technology of South Korea through National Research Lab Program.
文摘A nanocomposite of nickel oxide/carbon nanotubes was prepared through a simple chemical precipitation followed by thermal annealing. The electrochemical capacitance of this electrode material was studied. When the mass fraction of CNTs (carbon nanotubes) in NiO/CNT composites increases, the electrical resistivity of nanocomposites decreases and becomes similar to that of pure CNTs when it reaches 30%. The specific surface area of composites increases with increasing CNT mass fraction and the specific capacitance reaches 160 F/g under 10 mA/g discharge current density at CNT mass fraction of 10%.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.50875255 and 10902123)
文摘Periodic arrays of negative capacitance shunted piezoelectric patches are employed to control the band gaps of phononic beams. The location and the extent of induced band gap depend on the mismatch in impedance generated by each patch. The total impedance mismatch is determined by the added mass and stiffness of each patch as well as the shunting electrical impedance. Therefore, the band gap of the shunted phononic beam can be actively tuned by appropriately selecting the value of negative capacitance. The control of the band gap of phononic beam with negative capacitive shunt is demonstrated numerically by employing transfer matrix method. The result reveals that using negative capacitive shunt to tune the band gap is effective.
基金financially supported by the Research Project of Guangxi Zhuang Autonomous Region,China(Nos.1346011-7 and 1298019-11)the financial support from the Guangxi Hezhou Guidong Electronics Technology Co.,Ltd
文摘The morphology of etched aluminum foil was observed using scanning electron microscopy, which led to the establishment of a cylindrical model and two merged models, considering the fixed weight loss of etching. The maximum of specific capacitance and the cor- responding optimum values for tunnel sizes at various anodization voltages were predicted. The increased size distribution and taper of tun- nels were demonstrated to decrease the specific capacitance, whereas the addition of polymeric additive into the ttmnel widening solution was demonstrated to increase the capacitance. The formation of merged tunnels on the etched aluminum surface, irrespective of the presence of row-merged tunnels or cluster-merged tunnels, resulted in a dramatic decrease in the specific capacitance. It is concluded that, enhancing the uniformity of turmel size and distribution and avoiding the formation of merged tunnels are the effective approach to achieving the higher capacitance for the tunnel etched and formed aluminum foil.
基金financial support from National Natural Science Foundation of China(91534123,91834303,U1862117)supported by the State Key Laboratory of Multiphase Complex Systems(MPCS-2017-A-01)support by State key laboratory of Multiphase Complex Systems(MPCS)Facility Upgradation Program
文摘Here we report a strategy to enhance the energy density of supercapacitors by increasing the utilization rate of the specific surface area(SSA)via wettability improvement. The nonporous gold(NPG) film is used as the electrodes and the ionic liquid [EMIM]BF4 is the electrolyte. When the electrode is coated by paraffin, an increase of the contact angle leads to a remarkable reduction of the specific capacitance. While when acetonitrile is added into the electrolyte, the contact angle is decreased and the utilization rate of SSA is improved, which results in an increase of the specific capacitance. The addition of isopropyl acetate into the electrolyte leads to a further increase of the specific capacitance. To generalize the role of the wettability in improving the energy density, a carbon-based electrode is evaluated in the solution of potassium hydroxide. An addition of propyl alcohol into the potassium hydroxide solution leads to an increase of the specific capacitance, as well as a long-term stability of the supercapacitor. The role of conductivity in this study is excluded by designing experiments. This paper highlights the significance of wettability in determining the specific capacitance, showing an alternative to improve the energy density of supercapacitors.
