Surface charge accumulation on insulator surface can have great influence on surface flashover performance.An experimental system is established to investigate surface charge accumulation and decay characteristics of ...Surface charge accumulation on insulator surface can have great influence on surface flashover performance.An experimental system is established to investigate surface charge accumulation and decay characteristics of Al2O3-filled epoxy resin insulators in 0.1 MPa SF6 under DC voltages.Surface potential is recorded by a Kelvin vibrating probe connected to an electrostatic voltmeter.By pre-depositing charges on insulator surface,the influence of surface charges on surface flashover performance is studied.The results reveal that surface charge distribution appearance is the combined effect of electrode injection,back discharge and gas ionization.Surface charge distribution has obvious polarity effect.It is concentrated near the HV electrode under positive voltages and dispersed under negative voltages.The difference in positive and negative surface flashover voltage is attributed to the difference in surface charge distribution under DC voltages of different polarities.Surface charge decay contains two stages,which satisfies the law of double exponential function.At first stage,surface charge decays fast,which corresponds to charges escaping from shallower traps.While it decays slowly at the second stage,which corresponds to charge escaping from deeper traps.Surface charge decay process is dominated by surface conductivity mechanism.The pre-deposited charges on insulation surface have great influence on surface flashover performance.The deposited positive charges can increase positive flashover voltage but decrease negative flashover voltage.展开更多
In nature,the properties of matter are ultimately governed by the electronic structures.Quantum chemistry(QC)at electronic level matches well with a few simple physical assumptions in solving simple problems.To date,m...In nature,the properties of matter are ultimately governed by the electronic structures.Quantum chemistry(QC)at electronic level matches well with a few simple physical assumptions in solving simple problems.To date,machine learning(ML)algorithm has been migrated to this field to simplify calculations and improve fidelity.This review introduces the basic information on universal electron structures of emerging energy materials and ML algorithms involved in the prediction of material properties.Then,the structure-property relationships based on ML algorithm and QC theory are reviewed.Especially,the summary of recently reported applications on classifying crystal structure,modeling electronic structure,optimizing experimental method,and predicting performance is provided.Last,an outlook on ML assisted QC calculation towards identifying emerging energy materials is also presented.展开更多
The development and utilization of large-scale distributed power generation and the increase of impact loads represented by electric locomotives and new energy electric vehicles have brought great challenges to the st...The development and utilization of large-scale distributed power generation and the increase of impact loads represented by electric locomotives and new energy electric vehicles have brought great challenges to the stable operation of the regional power grid.To improve the prediction accuracy of power systems with source-load twoterminal uncertainties,an adaptive cubature Kalman filter algorithm based on improved initial noise covariance matrix Q0 is proposed in this paper.In the algorithm,the Q0 is used to offset the modeling error,and solves the problem of large voltage amplitude and phase fluctuation of the source-load two-terminal uncertain systems.Verification of the proposed method is implemented on the IEEE 30 node system through simulation.The results show that,compared with the traditional methods,the improved adaptive cubature Kalman filter has higher prediction accuracy,which verifies the effectiveness and accuracy of the proposed method in state estimation of the new energy power system with source-load two-terminal uncertainties.展开更多
The insulating paper of the transformer is affected by many factors during the operation,meanwhile,the surface texture of the paper is easy to change.To explore the relationship between the aging state and surface tex...The insulating paper of the transformer is affected by many factors during the operation,meanwhile,the surface texture of the paper is easy to change.To explore the relationship between the aging state and surface texture change of insulating paper,firstly,the thermal aging experiment of insulating paper is carried out,and the insulating paper samples with different aging times are obtained.After then,the images of the aged insulating paper samples are collected and pre-processed.The pre-processing effect is verified by constructing and calculating the gray surface of the sample.Secondly,the texture features of the insulating paper image are extracted by box dimension and multifractal spectrum.Based on that,the extreme learning machine(ELM)is taken as the classification tool with texture features and aging time as the input and output,to train the algorithm and construct the corresponding relationship between the texture feature and the aging time.After then,the insulating paper with unknown aging time is predicted with a trained ELMalgorithm.The numerical test results show that the texture features extracted from the fractal dimension of the micro image can effectively characterize the aging state of insulating paper,the average accuracy can reach 91.6%.It proves that the fractal dimension theory can be utilized for assessing the aging state of insulating paper for onsite applications.展开更多
The preventive effect of traditional Chinese medicine on the novel coronavirus(COVID-19)pneumonia is embodied in the"prevention before disease onset"of"treatment of disease"theory of thought,and it...The preventive effect of traditional Chinese medicine on the novel coronavirus(COVID-19)pneumonia is embodied in the"prevention before disease onset"of"treatment of disease"theory of thought,and it is considered that the key to the success or failure of prevention is whether the healthy qi is abundant or not.This article discusses and understands the"genuine qi"from the The Medical Classic of the Yellow Emperor,and describes its meaning comprehensively and systematically,combining with the expansion and supplement of many doctors in later generations.The"genuine qi"includes healthy qi,pulse qi,congenital qi,personal qi,Jing qi primordial qi and food energy,all of which are closely related to spleen-stomach.The function of spleen-stomach is normal,water and grain are transported properly,and the rise and fall of qi is appropriate,then the human body's qi is abundant,the anti-evil force is strong,and people are not easy to cause disease;even if the disease,the prognosis is better.This the novel coronavirus pneumonia comprehensive analysis,belongs to the traditional Chinese medicine science"damp-toxin epidemic",therefore the prevention should pay more attention to strengthen spleen and stomach,eliminate dampness,and Xiangsha Yangwei Pills is the appropriate choice.展开更多
With the growing demand for precise voltage adjustment and reactive regulation,the frequent operation of on-load tap changers(OLTCs)in oil-immersed systems has led to increased erosion of switch contacts by arcs durin...With the growing demand for precise voltage adjustment and reactive regulation,the frequent operation of on-load tap changers(OLTCs)in oil-immersed systems has led to increased erosion of switch contacts by arcs during the switching process.This erosion causes significant wear on the contacts,thereby reducing their lifespan.Therefore,the present study aims to investigate the behavior and mechanism of arc erosion on contact surfaces in oil-immersed OLTCs.To achieve this,a self-designed friction and wear test device for OLTC contacts was utilized to conduct experiments at various sliding speeds and contact pressures.Additionally,finite element analysis was employed to validate the experimental results regarding the influence of sliding speed on arc energy.The surface morphology of the contacts was observed using an optical microscope.The findings revealed that as the sliding speed increased,the arc energy,arc initiation rate,and contact resistance initially exhibited an upward trend,then decreased,and eventually increased again.The minimum values were observed at a sliding speed of 90 mm/s.Moreover,the arc energy,arc initiation rate,and contact resistance decreased gradually as the contact pressure increased.After reaching a contact pressure of 1.5 N,the variation in the arc energy stabilized.At lower contact pressures,arc erosion dominated the wear on the contact surface.However,at higher contact pressures,the wear transitioned from predominantly arc erosion to a combination of mechanical wear and arc erosion.In summary,experimental and analytical investigations provided insights into the effects of sliding speed and contact pressure on the behavior of arc erosion,contact resistance,and surface damage of OLTC contacts in oil-immersed systems.展开更多
DC-link capacitors play a vital role in managing ripple voltage and current in converters and various devices.This study focuses on exploring the aging characteristics of DC-link capacitors in alternating humid and th...DC-link capacitors play a vital role in managing ripple voltage and current in converters and various devices.This study focuses on exploring the aging characteristics of DC-link capacitors in alternating humid and thermal environments aligned with the operational conditions in photovoltaic and wind power applications.Adhering to relevant power equipment standards,we designed a 24-h alternating humid and thermal aging environment tailored to the requirements of DC-link capacitors.An aging test platform is established,and 20 widely used metallized polypropylene film capacitors are selected for evaluation.Parameters such as the capacitance,equivalent series resistance(ESR),and phase angle are assessed during aging,as well as the onset time and extent of aging at various intervals.This study focuses on the aging mechanisms,analyzing electrode corrosion,the self-healing process,and dielectric aging.Fitting the aging characteristics enabled us to calculate the lifespan of the capacitor and predict it under different degrees of capacitance decay.The results show that under alternating humid and thermal conditions,capacitance attenuation and ESR increase exhibit exponential nonlinearity,influenced by factors such as the oxidation and self-healing of capacitive metal electrodes,dielectric main-chain fracture,and crystal transformation.This study underscores the pivotal role of encapsulation in determining the aging decay time.展开更多
Composited cable terminals are critical for reliable power delivery of traditional and traction power supply systems.During its operation,the cable terminal continually undergoes complex circumstances where humidity,t...Composited cable terminals are critical for reliable power delivery of traditional and traction power supply systems.During its operation,the cable terminal continually undergoes complex circumstances where humidity,temperature,field strength,mechanical stress and other factors continuously change at different levels.In extreme cases,defects or even failures may occur in the cable terminals,leading to catastrophic accidents.This makes the condition monitoring and defect detection of composited cable terminals become an imperative need for the power industry.The“state-of-the-art”technology of cable terminal condition assessment is focussed and a systematic review of the current research progress of cable terminal condition assessment from the operation circumstances to failure mechanisms is provided.It covers both online/offline condition monitoring methods and defects detection approaches.In addition,challenges and future research directions for cable terminal condition assessment are also addressed.It is concluded that the non-destructive and non-intrusive methods like terahertz imaging and ultrasonic testing,and multi-source information fusion methods as well as the digital twin technology have been gaining popularity for cable terminal defect inspection.It is expected the presented work can provide a global field of vision for further advancement of both scholars and industrial engineers in this field.展开更多
An accurate extraction of vibration signal characteristics of an on-load tap changer(OLTC)during contact switching can effectively help detect its abnormal state.Therefore,an improved fuzzy C-means clustering method f...An accurate extraction of vibration signal characteristics of an on-load tap changer(OLTC)during contact switching can effectively help detect its abnormal state.Therefore,an improved fuzzy C-means clustering method for abnormal state detection of the OLTC contact is proposed.First,the wavelet packet and singular spectrum analysis are used to denoise the vibration signal generated by the moving and static contacts of the OLTC.Then,the Hilbert-Huang transform that is optimized by the ensemble empirical mode decomposition(EEMD)is used to decompose the vibration signal and extract the boundary spectrum features.Finally,the gray wolf algorithm-based fuzzy C-means clustering is used to denoise the signal and determine the abnormal states of the OLTC contact.An analysis of the experimental data shows that the proposed secondary denoising method has a better denoising effect compared to the single denoising method.The EEMD can improve the modal aliasing effect,and the improved fuzzy C-means clustering can effectively identify the abnormal state of the OLTC contacts.The analysis results of field measured data further verify the effectiveness of the proposed method and provide a reference for the abnormal state detection of the OLTC.展开更多
Nanocrystals of Rh, an important member of the noble metal catalyst family, have wide applications in heterogeneous catalytic reactions. Controlling the morphology of these noble metal nanocrystals has become an effec...Nanocrystals of Rh, an important member of the noble metal catalyst family, have wide applications in heterogeneous catalytic reactions. Controlling the morphology of these noble metal nanocrystals has become an effective strategy for improving their catalytic activity and durability. In this work, well-defined Rh nanodendrites with very thin triangular branches as subunits are synthesized using a facile diethylene glycol reduction method, assisted by polyethyleneimine as a complex-forming agent and surfactant. For the first time, the methanol oxidation reaction (MOR) on Rh nanocrystals with a well-defined morphology is investigated using various electrochemical techniques in an alkaline medium. Unexpectedly, the as-prepared Rh nanodendrites, with ultrathin nanosheet subunits, exhibit superior electrocatalytic activity and durability during the MOR in an alkaline medium, indicating that Rh nanocrystals with specific morphology may be highly promising alternatives to Pt electrocatalysts in the MOR in an alkaline medium.展开更多
Deposition of platinum(Pt)monolayers(PtML)on Au substrate represents a robust strategy to maximally utilize the Pt atoms and meanwhile achieve high catalytic activity towards methanol oxidation reaction for direct met...Deposition of platinum(Pt)monolayers(PtML)on Au substrate represents a robust strategy to maximally utilize the Pt atoms and meanwhile achieve high catalytic activity towards methanol oxidation reaction for direct methanol fuel cells owing to a substrate-induced tensile strain effect.However,recent studies showed that Pt(ML)on Au substrate are far from perfect smooth monoatomic layer,but actually exhibited three-dimensional nanoclusters.Moreover,the Pt(ML)suffered from severe structural instability and thus activity degradation during long-term electrocatalysis.To regulate the growth of Pt(ML)Au surface and also to improve its structural stability,we exploit dealloyed AuCu core-shell nanoparticles as a new substrate for depositing Pt(ML).By using high-resolution scanning transmission electron microscopy and energy dispersive X-ray elemental mapping combined with electrochemical characte rizations,we reveal that the dealloyed AuCu core-shell nanoparticles can effectively promote the deposition of Pt(ML)closer to a smooth monolayer structure,thus leading to a higher utilization efficiency of Pt and higher intrinsic activity towards methanol oxidation compared to those on pure Au nanoparticles.Moreover,the Pt(ML)deposited on the AuCu core-shell NPs showed substa ntially enhanced stability compared to those on pure Au NPs during long-term electrocatalysis over several hours,during which segregation of Cu to the Au/Pt interface was revealed and suggested to play an important role in stabilizing the Pt(ML)catalysts.展开更多
Low-platinum(Pt)alloy catalysts hold promising application in oxygen reduction reaction(ORR)electrocatalysis of protonexchange-membrane fuel cells(PEMFCs).Although significant progress has been made to boost the kinet...Low-platinum(Pt)alloy catalysts hold promising application in oxygen reduction reaction(ORR)electrocatalysis of protonexchange-membrane fuel cells(PEMFCs).Although significant progress has been made to boost the kinetic ORR mass activity at low current densities in liquid half-cells,little attention was paid to the performance of Pt-based catalysts in realistic PEMFCs particularly at high current densities for high power density,which remains poorly understood.In this paper,we show that,regardless of the kinetic mass activity at the low current density region,the high current density performance of the low-Pt alloy catalysts is dominantly controlled by the total Pt surface area,particularly in low-Pt-loading H_(2)–air PEMFCs.To this end,we propose two different strategies to boost the specific Pt surface area,the post-15-nm dealloyed nanoporous architecture and the sub-5-nm solid core–shell nanoparticles(NPs)through fluidic-bed synthesis,both of which bring in comparably high mass activity and high Pt surface area for large-current-density performance.At medium current density,the dealloyed porous NPs provide substantially higher H_(2)–air PEMFC performance compared to solid core–shell catalysts,despite their similar mass activity in liquid half-cells.Scanning transmission electron microscopy images combined with electron energy loss spectroscopic imaging evidence a previously unreported“semi-immersed nanoporous-Pt/ionomer”structure in contrast to a“fully-immersed core–shellPt/ionomer”structure,thus favoring O_(2) transport and improving the fuel cell performance.Our results provide new insights into the role of Pt nanostructures in concurrently optimizing the mass activity,Pt surface area and Pt/Nafion interface for high power density fuel cells.展开更多
文摘Surface charge accumulation on insulator surface can have great influence on surface flashover performance.An experimental system is established to investigate surface charge accumulation and decay characteristics of Al2O3-filled epoxy resin insulators in 0.1 MPa SF6 under DC voltages.Surface potential is recorded by a Kelvin vibrating probe connected to an electrostatic voltmeter.By pre-depositing charges on insulator surface,the influence of surface charges on surface flashover performance is studied.The results reveal that surface charge distribution appearance is the combined effect of electrode injection,back discharge and gas ionization.Surface charge distribution has obvious polarity effect.It is concentrated near the HV electrode under positive voltages and dispersed under negative voltages.The difference in positive and negative surface flashover voltage is attributed to the difference in surface charge distribution under DC voltages of different polarities.Surface charge decay contains two stages,which satisfies the law of double exponential function.At first stage,surface charge decays fast,which corresponds to charges escaping from shallower traps.While it decays slowly at the second stage,which corresponds to charge escaping from deeper traps.Surface charge decay process is dominated by surface conductivity mechanism.The pre-deposited charges on insulation surface have great influence on surface flashover performance.The deposited positive charges can increase positive flashover voltage but decrease negative flashover voltage.
基金supported by the National Natural Science Foundation of China(grant number 51872157)Shenzhen Technical Plan Project(grant number KQJSCX20160226191136 and JCYJ20170412170911187)Research Grants Council of the Hong Kong Special Administrative Region,China[grant number PF17-10186]。
文摘In nature,the properties of matter are ultimately governed by the electronic structures.Quantum chemistry(QC)at electronic level matches well with a few simple physical assumptions in solving simple problems.To date,machine learning(ML)algorithm has been migrated to this field to simplify calculations and improve fidelity.This review introduces the basic information on universal electron structures of emerging energy materials and ML algorithms involved in the prediction of material properties.Then,the structure-property relationships based on ML algorithm and QC theory are reviewed.Especially,the summary of recently reported applications on classifying crystal structure,modeling electronic structure,optimizing experimental method,and predicting performance is provided.Last,an outlook on ML assisted QC calculation towards identifying emerging energy materials is also presented.
基金supported by the Tianyou Youth Talent Lift Program of Lanzhou Jiaotong University,the Nature Science Foundation of Gansu(No.21JR1RA255)the Gansu University Innovation Fund Project(Nos.2020A-036 and 2021B-111).
文摘The development and utilization of large-scale distributed power generation and the increase of impact loads represented by electric locomotives and new energy electric vehicles have brought great challenges to the stable operation of the regional power grid.To improve the prediction accuracy of power systems with source-load twoterminal uncertainties,an adaptive cubature Kalman filter algorithm based on improved initial noise covariance matrix Q0 is proposed in this paper.In the algorithm,the Q0 is used to offset the modeling error,and solves the problem of large voltage amplitude and phase fluctuation of the source-load two-terminal uncertain systems.Verification of the proposed method is implemented on the IEEE 30 node system through simulation.The results show that,compared with the traditional methods,the improved adaptive cubature Kalman filter has higher prediction accuracy,which verifies the effectiveness and accuracy of the proposed method in state estimation of the new energy power system with source-load two-terminal uncertainties.
基金This work was supported by the Tianyou Youth Talent Lift Program of Lanzhou Jiaotong University,the Youth Science Foundation of Lanzhou Jiaotong University(No.2019029)the University Innovation Fund Project of Gansu Provincial Department of Education(No.2020A-036)the Young Doctor Foundation of JYT.GANSU.GOV.CN(No.2021QB-060).
文摘The insulating paper of the transformer is affected by many factors during the operation,meanwhile,the surface texture of the paper is easy to change.To explore the relationship between the aging state and surface texture change of insulating paper,firstly,the thermal aging experiment of insulating paper is carried out,and the insulating paper samples with different aging times are obtained.After then,the images of the aged insulating paper samples are collected and pre-processed.The pre-processing effect is verified by constructing and calculating the gray surface of the sample.Secondly,the texture features of the insulating paper image are extracted by box dimension and multifractal spectrum.Based on that,the extreme learning machine(ELM)is taken as the classification tool with texture features and aging time as the input and output,to train the algorithm and construct the corresponding relationship between the texture feature and the aging time.After then,the insulating paper with unknown aging time is predicted with a trained ELMalgorithm.The numerical test results show that the texture features extracted from the fractal dimension of the micro image can effectively characterize the aging state of insulating paper,the average accuracy can reach 91.6%.It proves that the fractal dimension theory can be utilized for assessing the aging state of insulating paper for onsite applications.
文摘The preventive effect of traditional Chinese medicine on the novel coronavirus(COVID-19)pneumonia is embodied in the"prevention before disease onset"of"treatment of disease"theory of thought,and it is considered that the key to the success or failure of prevention is whether the healthy qi is abundant or not.This article discusses and understands the"genuine qi"from the The Medical Classic of the Yellow Emperor,and describes its meaning comprehensively and systematically,combining with the expansion and supplement of many doctors in later generations.The"genuine qi"includes healthy qi,pulse qi,congenital qi,personal qi,Jing qi primordial qi and food energy,all of which are closely related to spleen-stomach.The function of spleen-stomach is normal,water and grain are transported properly,and the rise and fall of qi is appropriate,then the human body's qi is abundant,the anti-evil force is strong,and people are not easy to cause disease;even if the disease,the prognosis is better.This the novel coronavirus pneumonia comprehensive analysis,belongs to the traditional Chinese medicine science"damp-toxin epidemic",therefore the prevention should pay more attention to strengthen spleen and stomach,eliminate dampness,and Xiangsha Yangwei Pills is the appropriate choice.
文摘With the growing demand for precise voltage adjustment and reactive regulation,the frequent operation of on-load tap changers(OLTCs)in oil-immersed systems has led to increased erosion of switch contacts by arcs during the switching process.This erosion causes significant wear on the contacts,thereby reducing their lifespan.Therefore,the present study aims to investigate the behavior and mechanism of arc erosion on contact surfaces in oil-immersed OLTCs.To achieve this,a self-designed friction and wear test device for OLTC contacts was utilized to conduct experiments at various sliding speeds and contact pressures.Additionally,finite element analysis was employed to validate the experimental results regarding the influence of sliding speed on arc energy.The surface morphology of the contacts was observed using an optical microscope.The findings revealed that as the sliding speed increased,the arc energy,arc initiation rate,and contact resistance initially exhibited an upward trend,then decreased,and eventually increased again.The minimum values were observed at a sliding speed of 90 mm/s.Moreover,the arc energy,arc initiation rate,and contact resistance decreased gradually as the contact pressure increased.After reaching a contact pressure of 1.5 N,the variation in the arc energy stabilized.At lower contact pressures,arc erosion dominated the wear on the contact surface.However,at higher contact pressures,the wear transitioned from predominantly arc erosion to a combination of mechanical wear and arc erosion.In summary,experimental and analytical investigations provided insights into the effects of sliding speed and contact pressure on the behavior of arc erosion,contact resistance,and surface damage of OLTC contacts in oil-immersed systems.
基金Supported by the Opening Project of State Key Laboratory of Large Electric Drive System and Equipment Technology(SKLLDJ022020004).
文摘DC-link capacitors play a vital role in managing ripple voltage and current in converters and various devices.This study focuses on exploring the aging characteristics of DC-link capacitors in alternating humid and thermal environments aligned with the operational conditions in photovoltaic and wind power applications.Adhering to relevant power equipment standards,we designed a 24-h alternating humid and thermal aging environment tailored to the requirements of DC-link capacitors.An aging test platform is established,and 20 widely used metallized polypropylene film capacitors are selected for evaluation.Parameters such as the capacitance,equivalent series resistance(ESR),and phase angle are assessed during aging,as well as the onset time and extent of aging at various intervals.This study focuses on the aging mechanisms,analyzing electrode corrosion,the self-healing process,and dielectric aging.Fitting the aging characteristics enabled us to calculate the lifespan of the capacitor and predict it under different degrees of capacitance decay.The results show that under alternating humid and thermal conditions,capacitance attenuation and ESR increase exhibit exponential nonlinearity,influenced by factors such as the oxidation and self-healing of capacitive metal electrodes,dielectric main-chain fracture,and crystal transformation.This study underscores the pivotal role of encapsulation in determining the aging decay time.
基金National Natural Science Foundation of China,Grant/Award Number:52167018。
文摘Composited cable terminals are critical for reliable power delivery of traditional and traction power supply systems.During its operation,the cable terminal continually undergoes complex circumstances where humidity,temperature,field strength,mechanical stress and other factors continuously change at different levels.In extreme cases,defects or even failures may occur in the cable terminals,leading to catastrophic accidents.This makes the condition monitoring and defect detection of composited cable terminals become an imperative need for the power industry.The“state-of-the-art”technology of cable terminal condition assessment is focussed and a systematic review of the current research progress of cable terminal condition assessment from the operation circumstances to failure mechanisms is provided.It covers both online/offline condition monitoring methods and defects detection approaches.In addition,challenges and future research directions for cable terminal condition assessment are also addressed.It is concluded that the non-destructive and non-intrusive methods like terahertz imaging and ultrasonic testing,and multi-source information fusion methods as well as the digital twin technology have been gaining popularity for cable terminal defect inspection.It is expected the presented work can provide a global field of vision for further advancement of both scholars and industrial engineers in this field.
文摘An accurate extraction of vibration signal characteristics of an on-load tap changer(OLTC)during contact switching can effectively help detect its abnormal state.Therefore,an improved fuzzy C-means clustering method for abnormal state detection of the OLTC contact is proposed.First,the wavelet packet and singular spectrum analysis are used to denoise the vibration signal generated by the moving and static contacts of the OLTC.Then,the Hilbert-Huang transform that is optimized by the ensemble empirical mode decomposition(EEMD)is used to decompose the vibration signal and extract the boundary spectrum features.Finally,the gray wolf algorithm-based fuzzy C-means clustering is used to denoise the signal and determine the abnormal states of the OLTC contact.An analysis of the experimental data shows that the proposed secondary denoising method has a better denoising effect compared to the single denoising method.The EEMD can improve the modal aliasing effect,and the improved fuzzy C-means clustering can effectively identify the abnormal state of the OLTC contacts.The analysis results of field measured data further verify the effectiveness of the proposed method and provide a reference for the abnormal state detection of the OLTC.
基金This work was supported by National Natural Science Foundation of China (No. 21473111), Natural Science Foundation of Shaanxi Province (No. 2015JM2043),and Fundamental Research Funds for the Central Universities (Nos. GK201602002 and GK201503037).
文摘Nanocrystals of Rh, an important member of the noble metal catalyst family, have wide applications in heterogeneous catalytic reactions. Controlling the morphology of these noble metal nanocrystals has become an effective strategy for improving their catalytic activity and durability. In this work, well-defined Rh nanodendrites with very thin triangular branches as subunits are synthesized using a facile diethylene glycol reduction method, assisted by polyethyleneimine as a complex-forming agent and surfactant. For the first time, the methanol oxidation reaction (MOR) on Rh nanocrystals with a well-defined morphology is investigated using various electrochemical techniques in an alkaline medium. Unexpectedly, the as-prepared Rh nanodendrites, with ultrathin nanosheet subunits, exhibit superior electrocatalytic activity and durability during the MOR in an alkaline medium, indicating that Rh nanocrystals with specific morphology may be highly promising alternatives to Pt electrocatalysts in the MOR in an alkaline medium.
基金financial supports by National Natural Science Foundation of China(NSFC,Nos.21573123,51622103)the Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program(No.2017BT01N111)+1 种基金Guangdong Natural Science Foundation for Distinguished Young Scholars(No.2016A030306035)Basic Research Program of Shenzhen(No.JCYJ20160531194754308)in China。
文摘Deposition of platinum(Pt)monolayers(PtML)on Au substrate represents a robust strategy to maximally utilize the Pt atoms and meanwhile achieve high catalytic activity towards methanol oxidation reaction for direct methanol fuel cells owing to a substrate-induced tensile strain effect.However,recent studies showed that Pt(ML)on Au substrate are far from perfect smooth monoatomic layer,but actually exhibited three-dimensional nanoclusters.Moreover,the Pt(ML)suffered from severe structural instability and thus activity degradation during long-term electrocatalysis.To regulate the growth of Pt(ML)Au surface and also to improve its structural stability,we exploit dealloyed AuCu core-shell nanoparticles as a new substrate for depositing Pt(ML).By using high-resolution scanning transmission electron microscopy and energy dispersive X-ray elemental mapping combined with electrochemical characte rizations,we reveal that the dealloyed AuCu core-shell nanoparticles can effectively promote the deposition of Pt(ML)closer to a smooth monolayer structure,thus leading to a higher utilization efficiency of Pt and higher intrinsic activity towards methanol oxidation compared to those on pure Au nanoparticles.Moreover,the Pt(ML)deposited on the AuCu core-shell NPs showed substa ntially enhanced stability compared to those on pure Au NPs during long-term electrocatalysis over several hours,during which segregation of Cu to the Au/Pt interface was revealed and suggested to play an important role in stabilizing the Pt(ML)catalysts.
基金supported by the National Natural Science Foundation of China(Nos.52173222,51622103 and 22109088)the Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program(No.2017BT01N111)+1 种基金Key Area Research and Development Program of Guangdong Province(No.2020B0909040003)Shenzhen Science and Technology Innovation Committee(Nos.WDZ20200819115243002 and JCYJ20190809172617313).
文摘Low-platinum(Pt)alloy catalysts hold promising application in oxygen reduction reaction(ORR)electrocatalysis of protonexchange-membrane fuel cells(PEMFCs).Although significant progress has been made to boost the kinetic ORR mass activity at low current densities in liquid half-cells,little attention was paid to the performance of Pt-based catalysts in realistic PEMFCs particularly at high current densities for high power density,which remains poorly understood.In this paper,we show that,regardless of the kinetic mass activity at the low current density region,the high current density performance of the low-Pt alloy catalysts is dominantly controlled by the total Pt surface area,particularly in low-Pt-loading H_(2)–air PEMFCs.To this end,we propose two different strategies to boost the specific Pt surface area,the post-15-nm dealloyed nanoporous architecture and the sub-5-nm solid core–shell nanoparticles(NPs)through fluidic-bed synthesis,both of which bring in comparably high mass activity and high Pt surface area for large-current-density performance.At medium current density,the dealloyed porous NPs provide substantially higher H_(2)–air PEMFC performance compared to solid core–shell catalysts,despite their similar mass activity in liquid half-cells.Scanning transmission electron microscopy images combined with electron energy loss spectroscopic imaging evidence a previously unreported“semi-immersed nanoporous-Pt/ionomer”structure in contrast to a“fully-immersed core–shellPt/ionomer”structure,thus favoring O_(2) transport and improving the fuel cell performance.Our results provide new insights into the role of Pt nanostructures in concurrently optimizing the mass activity,Pt surface area and Pt/Nafion interface for high power density fuel cells.