The influences of the mask wall angle on the current density distribution,shape of the evolving cavity and machining accuracy were investigated in electrochemical machining(ECM) by mask.A mathematical model was develo...The influences of the mask wall angle on the current density distribution,shape of the evolving cavity and machining accuracy were investigated in electrochemical machining(ECM) by mask.A mathematical model was developed to predict the shape evolution during the ECM by mask.The current density distribution is sensitive to mask wall angle.The evolution of cavity is determined by the current density distribution of evolving workpiece surface.The maximum depth is away from the center of holes machined,which leads to the island appearing at the center of cavity for mask wall angles greater than or equal to 90°(β≥90°).The experimental system was established and the simulation results were experimentally verified.The results indicate that the simulation results of cavity shape are consistent with the actual ones.The experiments also show that the repetition accuracy of matrix-hole for β≥90° is higher than that for β<90°.A hole taper is diminished,and the machining accuracy is improved with the mask wall angle increasing.展开更多
This article aims to investigate the transient behavior of a planar direct internal reforming solid oxide fuel cell (DIR-SOFC) comprehensively. A one-dimensional dynamic model of a planar D1R-SOFC is first developed...This article aims to investigate the transient behavior of a planar direct internal reforming solid oxide fuel cell (DIR-SOFC) comprehensively. A one-dimensional dynamic model of a planar D1R-SOFC is first developed based on mass and energy balances, and electrochemical principles. Further, a solution strategy is presented to solve the model, and the International Energy Agency (IEA) benchmark test is used to validate the model. Then, through model-based simulations, the steady-state performance of a co-flow planar DIR-SOFC under specified initial operating conditions and its dynamic response to introduced operating parameter disturbances are studied. The dynamic responses of important SOFC variables, such as cell temperature, current density, and cell voltage are all investigated when the SOFC is subjected to the step-changes in various operating parameters including both the load current and the inlet fuel and air flow rates. The results indicate that the rapid dynamics of the current density and the cell voltage are mainly influenced by the gas composition, particularly the H2 molar fraction in anode gas channels, while their slow dynamics are both dominated by the SOLID (including the PEN and interconnects) temperature. As the load current increases, the SOLID temperature and the maximum SOLID temperature gradient both increase, and thereby, the cell breakdown is apt to occur because of excessive thermal stresses. Changing the inlet fuel flow rate might lead to the change in the anode gas composition and the consequent change in the current density distribution and cell voltage. The inlet air flow rate has a great impact on the cell temperature distribution along the cell, and thus, is a suitable manipulated variable to control the cell temperature.展开更多
In order to obtain higher emission performance than that of a traditional M-type cathode, we have developed a new type impregnated dispenser cathode. The new cathode is impregnated with a new active substance with mol...In order to obtain higher emission performance than that of a traditional M-type cathode, we have developed a new type impregnated dispenser cathode. The new cathode is impregnated with a new active substance with molar ratio of 26BaO·29SrO·8Sc2O3 ·7CaO·Al2O3 . This paper introduces the emission performance, surface active material, and work function of the new cathode. At 1100℃B , the DC current density and pulse current density are 30.6±1.0 A/cm2 and 171.6±2.8 A/cm2 , respectively, 2.1 and 5.4 times of that of an M-type cathode. The work function of the new cathode is 1.668± 0.002 eV. High concentration O-Al-Sc-Sr-Ba and O-Al-Sc-Ba are found in the pores and at pore edges, respectively. By comparing the emission performances and surface characteristics of as-polished and as-cleaned cathodes, it is proposed that, the emission around pore ends forms the major part of the total emission for the new cathodes.展开更多
Exfoliated graphite oxide was prepared by an improved Hummers method and was then reduced to graphene with hydrazine in the presence of ammonium hydroxide.N2adsorption–desorption measurement showed that graphene so o...Exfoliated graphite oxide was prepared by an improved Hummers method and was then reduced to graphene with hydrazine in the presence of ammonium hydroxide.N2adsorption–desorption measurement showed that graphene so obtained had a specific surface area as high as 818 m2/g.Galvanostatic charge/discharge curves demonstrated that the as-prepared graphene exhibited a specific capacitance of 186.9 F/g at a current density of 0.1 A/g and that about 96%of the specific capacitance was retained after 2000 cycles at a current density of 5 A/g.展开更多
It is still challenging to develop suitable cathode structures for high-rate and stable aqueous Zn-ion batteries.Herein,a phosphating-assisted interfacial engineering strategy is designed for the controllable conversi...It is still challenging to develop suitable cathode structures for high-rate and stable aqueous Zn-ion batteries.Herein,a phosphating-assisted interfacial engineering strategy is designed for the controllable conversion of NiCo_(2)S_(4) nanosheets into heterostructured NiCoP/NiCo_(2)S_(4) as the cathodes in aqueous Zn-ion batteries.The multicomponent heterostructures with rich interfaces can not only improve the electrical conductivity but also enhance the diffusion pathways for Zn-ion storage.As expected,the NiCoP/NiCo_(2)S_(4) electrode has high performance with a large specific capacity of 251.1 mA h g^(−1) at a high current density of 10 A g^(−1) and excellent rate capability(retaining about 76%even at 50 A g^(−1)).Accordingly,the Zn-ion battery using NiCoP/NiCo_(2)S_(4) as the cathode delivers a high specific capacity(265.1 mA h g^(−1) at 5 A g^(−1)),a long-term cycling stability(96.9%retention after 5000 cycles),and a competitive energy density(444.7W h kg^(−1) at the power density of 8.4 kW kg^(−1)).This work therefore provides a simple phosphating-assisted interfacial engineering strategy to construct heterostructured electrode materials with rich interfaces for the development of high-performance energy storage devices in the future.展开更多
In this paper, the bacterial celluloses(BCs) were pyrolysed in nitrogen and then activated by KOH to form a porous three- dimension-network electrode material for supercapacitor applications. Activated pyrolysed bacte...In this paper, the bacterial celluloses(BCs) were pyrolysed in nitrogen and then activated by KOH to form a porous three- dimension-network electrode material for supercapacitor applications. Activated pyrolysed bacterial cellulose(APBC) samples with enlarged specific surface area and enhanced specific capacitances were obtained. In order to optimize electrochemical properties, APBC samples with different alkali-to-carbon ratios of 1, 2 and 3 were tested in two electrodes symmetrical capacitors. The optimized APBC sample holds the highest specific capacitance of 241.8 F/g, and the energy density of which is 5 times higher than that of PBC even at a current density of 5 A/g. This work presents a successful practice of preparing electrode material from environment-friendly biomass, bacterial cellulose.展开更多
Ru has recently been regarded as a promising catalyst for hydrogen oxidation reaction(HOR) and hydrogen evolution reaction(HER) due to its similar binding energy towards *H but lower price compared to Pt.Nevertheless,...Ru has recently been regarded as a promising catalyst for hydrogen oxidation reaction(HOR) and hydrogen evolution reaction(HER) due to its similar binding energy towards *H but lower price compared to Pt.Nevertheless, the quest of high-efficiency Ru-based catalysts for HOR and HER is driven by the current disadvantages including low activity and unsatisfactory stability. Herein, we have fabricated and engineered two-dimensional(2D) Ru-based snow-like nanosheets with Ru/Ru O2interface(Ru/Ru O2SNSs)via a post-annealing treatment. Detailed characterizations and theoretical calculations indicate that the interfacial synergy, which is dependent on the temperature for annealing, can alter the hydrogen binding energy(HBE) and hydroxide binding energy(OHBE), as a result of the enhanced HOR and HER performance. Impressively, the optimal Ru/RuO_(2) SNSs display a mass activity of 9.13 A mgRu^(–1) at an overpotential of 50 m V in 0.1 mol L^(–1) KOH for HOR, which is 65, 304, and 21 times higher than those of Ru SNSs(0.14 A mg_(Ru)^(–1)), RuO_(2) SNSs(0.03 A mg_(Ru)^(–1)), and commercial Pt/C(0.43 A mg_(Ru)^(–1)), respectively.Moreover, Ru/RuO_(2) SNSs display improved HER activity with a low overpotential of 20.2 m V for achieving10 m A cm^(-2)in 1 mol L^(–1)KOH. This work not only provides an efficient catalyst for HOR and HER, but also promotes fundamental research on the fabrication and modification of catalysts in heterogeneous catalysis.展开更多
Rapid improvement in the efficiency of GaN-based LEDs not only speed up its applications for general illumination, but offer the possibilities for data transmission. This review is to provide an overview of current pr...Rapid improvement in the efficiency of GaN-based LEDs not only speed up its applications for general illumination, but offer the possibilities for data transmission. This review is to provide an overview of current progresses of GaN-based LEDs for light communications. The modulation bandwidth of GaN-based LEDs has been first improved by optimizing the LED epilayer structures and the modulation bandwidth of 73 MHz was achieved at the driving current density of 40 A/cm2 by changing the multi-quantum well structures. After that, in order to increase the current density tolerance, different parallel flip-chip micro-LED arrays were fabricated. With a high injected current density of ~7900 A/cm2, a maximum modulation bandwidth of ~227 MHz was obtained with optical power greater than 30 mW. Besides the increase of carrier concentrations, the radiative recombination coefficient B was also enhanced by modifying the photon surrounding environment based on some novel nanostructures such as resonant cavity, surface plasmon, and photonic crystals. The optical 3 dB modulation bandwidth of GaN-based nanostructure LEDs with Ag nanoparticles was enhanced by 2 times compared with GaN-based nanostructure LEDs without Ag nanoparticles.Our results demonstrate that using the QW-SP coupling can effectively help to enhance the carrier spontaneous emission rate and also increase the modulation bandwidth for LEDs, especially for LEDs with high intrinsic IQE. In addition, we discuss the progress of the faster color conversion stimulated by GaN-based LEDs.展开更多
基金Project(50635040) supported by the National Natural Science Foundation of ChinaProject(2009AA044205) supported by the National High Technology Research and Development ProgramProject(BK2008043) supported by the Jiangsu Provincial Natural Science Foundation,China
文摘The influences of the mask wall angle on the current density distribution,shape of the evolving cavity and machining accuracy were investigated in electrochemical machining(ECM) by mask.A mathematical model was developed to predict the shape evolution during the ECM by mask.The current density distribution is sensitive to mask wall angle.The evolution of cavity is determined by the current density distribution of evolving workpiece surface.The maximum depth is away from the center of holes machined,which leads to the island appearing at the center of cavity for mask wall angles greater than or equal to 90°(β≥90°).The experimental system was established and the simulation results were experimentally verified.The results indicate that the simulation results of cavity shape are consistent with the actual ones.The experiments also show that the repetition accuracy of matrix-hole for β≥90° is higher than that for β<90°.A hole taper is diminished,and the machining accuracy is improved with the mask wall angle increasing.
基金Supported by the National High Technology Research and Development Program of China (2006AA05Z148)
文摘This article aims to investigate the transient behavior of a planar direct internal reforming solid oxide fuel cell (DIR-SOFC) comprehensively. A one-dimensional dynamic model of a planar D1R-SOFC is first developed based on mass and energy balances, and electrochemical principles. Further, a solution strategy is presented to solve the model, and the International Energy Agency (IEA) benchmark test is used to validate the model. Then, through model-based simulations, the steady-state performance of a co-flow planar DIR-SOFC under specified initial operating conditions and its dynamic response to introduced operating parameter disturbances are studied. The dynamic responses of important SOFC variables, such as cell temperature, current density, and cell voltage are all investigated when the SOFC is subjected to the step-changes in various operating parameters including both the load current and the inlet fuel and air flow rates. The results indicate that the rapid dynamics of the current density and the cell voltage are mainly influenced by the gas composition, particularly the H2 molar fraction in anode gas channels, while their slow dynamics are both dominated by the SOLID (including the PEN and interconnects) temperature. As the load current increases, the SOLID temperature and the maximum SOLID temperature gradient both increase, and thereby, the cell breakdown is apt to occur because of excessive thermal stresses. Changing the inlet fuel flow rate might lead to the change in the anode gas composition and the consequent change in the current density distribution and cell voltage. The inlet air flow rate has a great impact on the cell temperature distribution along the cell, and thus, is a suitable manipulated variable to control the cell temperature.
基金Supported by the National Natural Science Foundation of China (No. 60871053)the Major State Basic Research Development Program of China (No. 2013CB328901)
文摘In order to obtain higher emission performance than that of a traditional M-type cathode, we have developed a new type impregnated dispenser cathode. The new cathode is impregnated with a new active substance with molar ratio of 26BaO·29SrO·8Sc2O3 ·7CaO·Al2O3 . This paper introduces the emission performance, surface active material, and work function of the new cathode. At 1100℃B , the DC current density and pulse current density are 30.6±1.0 A/cm2 and 171.6±2.8 A/cm2 , respectively, 2.1 and 5.4 times of that of an M-type cathode. The work function of the new cathode is 1.668± 0.002 eV. High concentration O-Al-Sc-Sr-Ba and O-Al-Sc-Ba are found in the pores and at pore edges, respectively. By comparing the emission performances and surface characteristics of as-polished and as-cleaned cathodes, it is proposed that, the emission around pore ends forms the major part of the total emission for the new cathodes.
基金supported by the National Natural Science Foundation of China(Grant Nos.51072047,21271067)the Program for Innovative Research Team in University(Grant No.IRT-1237)
文摘Exfoliated graphite oxide was prepared by an improved Hummers method and was then reduced to graphene with hydrazine in the presence of ammonium hydroxide.N2adsorption–desorption measurement showed that graphene so obtained had a specific surface area as high as 818 m2/g.Galvanostatic charge/discharge curves demonstrated that the as-prepared graphene exhibited a specific capacitance of 186.9 F/g at a current density of 0.1 A/g and that about 96%of the specific capacitance was retained after 2000 cycles at a current density of 5 A/g.
基金supported by the National Natural Science Foundation of China(51602049 and 51708504)China Postdoctoral Science Foundation(2017M610217 and 2018T110322)。
文摘It is still challenging to develop suitable cathode structures for high-rate and stable aqueous Zn-ion batteries.Herein,a phosphating-assisted interfacial engineering strategy is designed for the controllable conversion of NiCo_(2)S_(4) nanosheets into heterostructured NiCoP/NiCo_(2)S_(4) as the cathodes in aqueous Zn-ion batteries.The multicomponent heterostructures with rich interfaces can not only improve the electrical conductivity but also enhance the diffusion pathways for Zn-ion storage.As expected,the NiCoP/NiCo_(2)S_(4) electrode has high performance with a large specific capacity of 251.1 mA h g^(−1) at a high current density of 10 A g^(−1) and excellent rate capability(retaining about 76%even at 50 A g^(−1)).Accordingly,the Zn-ion battery using NiCoP/NiCo_(2)S_(4) as the cathode delivers a high specific capacity(265.1 mA h g^(−1) at 5 A g^(−1)),a long-term cycling stability(96.9%retention after 5000 cycles),and a competitive energy density(444.7W h kg^(−1) at the power density of 8.4 kW kg^(−1)).This work therefore provides a simple phosphating-assisted interfacial engineering strategy to construct heterostructured electrode materials with rich interfaces for the development of high-performance energy storage devices in the future.
基金supported by the Ministry of Science and Technology of China (2012CB933403)the National Natural Science Foundation of China (21173057, 51425302)the Chinese Academy of Sciences.
文摘In this paper, the bacterial celluloses(BCs) were pyrolysed in nitrogen and then activated by KOH to form a porous three- dimension-network electrode material for supercapacitor applications. Activated pyrolysed bacterial cellulose(APBC) samples with enlarged specific surface area and enhanced specific capacitances were obtained. In order to optimize electrochemical properties, APBC samples with different alkali-to-carbon ratios of 1, 2 and 3 were tested in two electrodes symmetrical capacitors. The optimized APBC sample holds the highest specific capacitance of 241.8 F/g, and the energy density of which is 5 times higher than that of PBC even at a current density of 5 A/g. This work presents a successful practice of preparing electrode material from environment-friendly biomass, bacterial cellulose.
基金supported by the National Key R&D Program of China(2020YFB1505802)the Ministry of Science and Technology of China(2017YFA0208200,2016YFA0204100)+4 种基金the National Natural Science Foundation of China(22025108,U21A20327,and22121001)China Postdoctoral Science Foundation(2020M682083)Guangdong Provincial Natural Science Fund for Distinguished Young Scholars(2021B1515020081)Start-up Support from Xiamen University and the Guangzhou Key Laboratory of Low Dimensional Materials and Energy Storage Devices(20195010002)。
文摘Ru has recently been regarded as a promising catalyst for hydrogen oxidation reaction(HOR) and hydrogen evolution reaction(HER) due to its similar binding energy towards *H but lower price compared to Pt.Nevertheless, the quest of high-efficiency Ru-based catalysts for HOR and HER is driven by the current disadvantages including low activity and unsatisfactory stability. Herein, we have fabricated and engineered two-dimensional(2D) Ru-based snow-like nanosheets with Ru/Ru O2interface(Ru/Ru O2SNSs)via a post-annealing treatment. Detailed characterizations and theoretical calculations indicate that the interfacial synergy, which is dependent on the temperature for annealing, can alter the hydrogen binding energy(HBE) and hydroxide binding energy(OHBE), as a result of the enhanced HOR and HER performance. Impressively, the optimal Ru/RuO_(2) SNSs display a mass activity of 9.13 A mgRu^(–1) at an overpotential of 50 m V in 0.1 mol L^(–1) KOH for HOR, which is 65, 304, and 21 times higher than those of Ru SNSs(0.14 A mg_(Ru)^(–1)), RuO_(2) SNSs(0.03 A mg_(Ru)^(–1)), and commercial Pt/C(0.43 A mg_(Ru)^(–1)), respectively.Moreover, Ru/RuO_(2) SNSs display improved HER activity with a low overpotential of 20.2 m V for achieving10 m A cm^(-2)in 1 mol L^(–1)KOH. This work not only provides an efficient catalyst for HOR and HER, but also promotes fundamental research on the fabrication and modification of catalysts in heterogeneous catalysis.
基金supported by the National Natural Science Foundation of China(Grant No.11574306)the China International Science and Technology Cooperation Program(Grant No.2014DFG62280)the National High Technology Program of China(Grant No.2015AA03A101)
文摘Rapid improvement in the efficiency of GaN-based LEDs not only speed up its applications for general illumination, but offer the possibilities for data transmission. This review is to provide an overview of current progresses of GaN-based LEDs for light communications. The modulation bandwidth of GaN-based LEDs has been first improved by optimizing the LED epilayer structures and the modulation bandwidth of 73 MHz was achieved at the driving current density of 40 A/cm2 by changing the multi-quantum well structures. After that, in order to increase the current density tolerance, different parallel flip-chip micro-LED arrays were fabricated. With a high injected current density of ~7900 A/cm2, a maximum modulation bandwidth of ~227 MHz was obtained with optical power greater than 30 mW. Besides the increase of carrier concentrations, the radiative recombination coefficient B was also enhanced by modifying the photon surrounding environment based on some novel nanostructures such as resonant cavity, surface plasmon, and photonic crystals. The optical 3 dB modulation bandwidth of GaN-based nanostructure LEDs with Ag nanoparticles was enhanced by 2 times compared with GaN-based nanostructure LEDs without Ag nanoparticles.Our results demonstrate that using the QW-SP coupling can effectively help to enhance the carrier spontaneous emission rate and also increase the modulation bandwidth for LEDs, especially for LEDs with high intrinsic IQE. In addition, we discuss the progress of the faster color conversion stimulated by GaN-based LEDs.