The transition of hydrogen sourcing from carbon-intensive to water-based methodologies is underway,with renewable energy-powered proton exchange membrane water electrolysis(PEMWE)emerging as the preeminent pathway for...The transition of hydrogen sourcing from carbon-intensive to water-based methodologies is underway,with renewable energy-powered proton exchange membrane water electrolysis(PEMWE)emerging as the preeminent pathway for hydrogen production.Despite remarkable advancements in this field,confronting the sluggish electrochemical kinetics and inherent high-energy consumption arising from deteriorated mass transport within PEMWE systems remains a formidable obstacle.This impediment stems primarily from the hindered protons mass transfer and the untimely hydrogen bubbles detachment.To address these challenges,we harness the inherent variability of electrical energy and introduce an innovative pulsed dynamic water electrolysis system.Compared to constant voltage electrolysis(hydrogen production rate:51.6 m L h^(-1),energy consumption:5.37 kWh Nm-^(3)H_(2)),this strategy(hydrogen production rate:66 m L h^(-1),energy consumption:3.83 kWh Nm-^(3)H_(2))increases the hydrogen production rate by approximately 27%and reduces the energy consumption by about 28%.Furthermore,we demonstrate the practicality of this system by integrating it with an off-grid photovoltaic(PV)system designed for outdoor operation,successfully driving a hydrogen production current of up to 500 mA under an average voltage of approximately 2 V.The combined results of in-situ characterization and finite element analysis reveal the performance enhancement mechanism:pulsed dynamic electrolysis(PDE)dramatically accelerates the enrichment of protons at the electrode/solution interface and facilitates the release of bubbles on the electrode surface.As such,PDE-enhanced PEMWE represents a synergistic advancement,concurrently enhancing both the hydrogen generation reaction and associated transport processes.This promising technology not only redefines the landscape of electrolysis-based hydrogen production but also holds immense potential for broadening its application across a diverse spectrum of electrocatalytic endeavors.展开更多
Lithium-ion batteries with LiCoO_(2)(LCO)cathodes are widely used in various electronic devices,resulting in a large amount of spent LCO(SLCO).Therefore,there is an urgent need for an efficient technique for recycling...Lithium-ion batteries with LiCoO_(2)(LCO)cathodes are widely used in various electronic devices,resulting in a large amount of spent LCO(SLCO).Therefore,there is an urgent need for an efficient technique for recycling SLCO.However,due to the presence of cobalt oxide with a spinel phase on the surface of highly-degraded LCO,the strong electrostatic repulsion from the transition metal octahedron poses a high Li replenishment barrier,making the regeneration of highly-degraded LCO a challenge.Herein,we propose a structural transformation strategy for reconstructing Li replenishment channels to aid the direct regeneration of highly-degraded LCO.In this approach,ball milling is employed to disrupt the inherent structure of highly-degraded LCO,thereby releasing the internal stress and converting the surface spinel phase into a homogeneous amorphous structure,which promotes Li insertion and regeneration.The regenerated LCO(RLCO)exhibits an outstanding discharge capacity of 179.10 mAh·g^(−1) in the voltage range of 3.0–4.5 V at 0.5 C.The proposed strategy is an effective regeneration approach for highly-degraded LCO,thereby facilitating the efficient recycling of spent lithium-ion battery cathode materials.展开更多
The ultra-light Mg–8Li–3Al–2Zn–0.5Y(LAZ832–0.5Y)thin wall parts with excellent performances were successfully fabricated by Gas Tungsten Arc Welding(GTAW)in this study.The microstructure of the top,middle and bot...The ultra-light Mg–8Li–3Al–2Zn–0.5Y(LAZ832–0.5Y)thin wall parts with excellent performances were successfully fabricated by Gas Tungsten Arc Welding(GTAW)in this study.The microstructure of the top,middle and bottom regions of the thin wall fabricated under various conditions was examined and the mechanical properties of these thin walls were tested.The results showed that much finer microstructure was obtained by GTAW than that made by conventional casting method.In the as-deposited samples,the needle-like shapedα-Mg phase emerged at the top of the thin wall whereas the bar-shapedα-Mg phase showed up in the middle and bottom regions of the thin wall due to the complex thermal history.The Al2Y phase was dispersed throughout bothα-Mg andβ-Li while the AlLi phase was mainly located in theβ-Li.The best combination of ultimate tensile strength(UTS),yield strength(YS)and elongation to fracture of the as-deposited thin wall were 218.9 MPa,171.4 MPa and 20.9%,respectively,which was manufactured under the optimal condition of 120 A 1800 mm/min 220 mm/min.After solid solution treatment at 350℃for 4 h,the UTS increased slightly by 13%but the YS increased significantly by 65%compared with the samples before solid solution.The solution of the AlLi phase was believed to be the main strengthening mechanism.It is interesting to note that the UTS and YS of the as-deposited sample was better than those of the as-cast sample while the opposite situation took place after solid solution treatment.展开更多
Rational design of catalytic interfaces at the atomic level is crucial for enhancing electrocatalytic CO_(2)reduction.In this study,a Zeolite imidazolate frameworks-8 derived catalyst is developed,featuring atomically...Rational design of catalytic interfaces at the atomic level is crucial for enhancing electrocatalytic CO_(2)reduction.In this study,a Zeolite imidazolate frameworks-8 derived catalyst is developed,featuring atomically dispersed Ni–Zn dual-atom sites(NiZnN_(6))coexisting with Ni_(3)ZnC_(0.7) nanoparticles on nitrogen-doped carbon nanotubes.Strong interaction between the NiZnN_(6) moieties and Ni_(3)ZnC_(0.7) nanoparticle induces charge redistribution,enhancing the electron-donating ability of Ni active sites.Simultaneously,the dual-atom configuration creates an asymmetric electronic environment,where interfacial electronic coupling facilitates partial electron transfer from Zn to Ni,leading to electron enrichment at the Ni center.Consequently,Ni sites preferentially donate electrons to active CO_(2)molecules,lowering the ^(*)COOH formation energy,while Zn sites promote ^(*)CO desorption,thus achieving high CO selectivity(99.6%@-0.7V vs.Reversible Hydrogen Electrode(RHE)).The in-depth investigation in this work provides guidance for establishing the relationship between structure and electrocatalytic activity,holding significant implications for fundamental research on the CO_(2)reduction mechanism.展开更多
Soil water-stable aggregates (WSAs) are the basic unit of soil constitution and can contribute to remaining the stable soil constitution. The objective of this study was to clarify the distribution and stability of WS...Soil water-stable aggregates (WSAs) are the basic unit of soil constitution and can contribute to remaining the stable soil constitution. The objective of this study was to clarify the distribution and stability of WSAs and the soil organic carbon (SOC), the total nitrogen (TN), and the total phosphorus (TP) concentrations in 0 - 20 cm and 20 - 40 cm soil layers under the different ages of Robinia pseudoacacia plantations. The 20, 25, 40, and 50 years-old Robinia pseudoacacia plantations were selected. Stepwise regression analysis showed that >5 mm and 1 - 2 mm WSAs, SOC concentration in 2 - 5 mm WSAs, and TN and TP concentrations in < 0.25 mm WSAs were dominant independent variables affecting aggregate stability and that SOC in 0.25 - 0.5 mm WSAs, TN in <0.25 mm and 1 - 2 mm WSAs and TP in 2 - 5 mm WSAs were dominant independent variables affecting SOC, TN, and TP concentrations in bulk soils.展开更多
Aluminum-metal batteries show great potential as next-generation energy storage due to their abundant resources and intrinsic safety.However,the crucial limitations of metallic Al anodes,such as dendrite and corrosion...Aluminum-metal batteries show great potential as next-generation energy storage due to their abundant resources and intrinsic safety.However,the crucial limitations of metallic Al anodes,such as dendrite and corrosion problems in conventional aluminum-metal batteries,remain challenging and elusive.Here,we report a novel electrodeposition strategy to prepare an optimized 3D Al anode on carbon cloth with an uniform deposition morphology,low local current density,and mitigatory volume change.The symmetrical cells with the 3D Al anode show superior stable cycling(>450 h)and low-voltage hysteresis(~170 mV)at 0.5 mA cm^(−2).High reversibility(~99.7%)is achieved for the Al plating/stripping.The graphite||Al‐4/CC full batteries show a long lifespan of 800 cycles with 54 mAh g^(−1) capacity at a high current density of 1000 mA g^(−1),benefiting from the high capacitive-controlled distribution.This study proposes a novel strategy to design 3D Al anodes for metallic-Al-based batteries by eliminating the problems of planar Al anodes and realizing the potential applications of aluminum-graphite batteries.展开更多
Polystyrene resins(PS)have been practical ion exchangers for radionuclides removal from water.However,nonspecific effects of ion exchange groups continue to be a major obstacle for emergency treatment with coexisting ...Polystyrene resins(PS)have been practical ion exchangers for radionuclides removal from water.However,nonspecific effects of ion exchange groups continue to be a major obstacle for emergency treatment with coexisting ions of high concentrations.The selectivity for Cs+enables zirconium phosphate(ZrP)to be the most promising inorganic sorbent for radioactive cesium extraction,despite being difficult to synthesize and causing excessive pressure loss in fixed-bed reactors due to fine powder.Herein,through facile confined crystallization in host macropores,we prepared PS confinedα-ZrP nanocrystalline(ZrP-PS).Size-screen sorption of layeredα-ZrP and sulfonic acid group preconcentration of PS synergistically enable a considerably higher Cs+affinity of ZrP-PS than PS,as confirmed by X-ray photoelectron spectroscopy(XPS)analysis.ZrP-PS demonstrated remarkable cesium sequestration performance in both batch and continuous experiments,with a high adsorption capacity of 269.58 mg/g,a rapid equilibrium within 80 min,and a continuous effluent volume of 2300 L/kg sorbents.Given the excellent selectivity for Cs+and flexibility to separate from treated water,ZrP-PS holds great promise as purification packages for the emergency treatment of radioactively contaminated water.展开更多
The“shuttle effect”of lithium polysulfides(LiPSs)is a huge challenge for practical use of high-energydensity lithium-sulfur(Li-S)batteries,and one of the main reasons is the sluggish kinetics of sulfur conversion.Me...The“shuttle effect”of lithium polysulfides(LiPSs)is a huge challenge for practical use of high-energydensity lithium-sulfur(Li-S)batteries,and one of the main reasons is the sluggish kinetics of sulfur conversion.Metal oxides are able to expedite the sulfur electrochemistry,and the structural defects enhance the adsorption-conversion ability of metal oxides for polysulfides.However,a significant research gap still remains regarding the relationship between the oxygen vacancy concentration and the adsorptivecatalytic performance of metal oxides.Herein,we establish a correlation between oxygen vacancy concentration and adsorptive-catalytic properties by using tungsten oxide(WO_(x))as model catalysts.It is revealed that high-concentration oxygen vacancy is beneficial for enhancing the binding between tungsten oxide and LiPSs,reducing the energy barrier of Li_(2)S decomposition,and promoting polysulfide conversion kinetics.Consequently,the Li-S batteries using the tungsten oxide with high-concentration oxygen vacancies deliver high initial discharge capacity of 1169 mA h g^(-1)at 0.2 C and 865 mA h g^(-1)at 2 C,low attenuation rate of 0.064%per cycle over 1100 cycles at 2 C.With a high sulfur area loading of 5.34 mg cm^(-2),the Li-S batteries still exhibit high initial gravimetric capacity of 982 mA h g^(-1)at 0.1 C and areal capacity of 5.92 mA h cm^(-2).This work promotes the feasibility of defect engineering on metal oxides as an effective mean to enhance the practicality of Li-S batteries.展开更多
The Electro-Fenton(EF)process is one of the promising advanced oxidation processes(AOPs)for environmental remediation.The H_(2)O_(2) yield of EF process largely determines its performance on organic pollutants degrada...The Electro-Fenton(EF)process is one of the promising advanced oxidation processes(AOPs)for environmental remediation.The H_(2)O_(2) yield of EF process largely determines its performance on organic pollutants degradation.Conventional Pd-catalytic EF process generates H_(2)O_(2) via the combination reaction of anodic O_(2) and cathodic H;.However,the relatively expensive catalyst limits its application.Herein,a hybrid Pd/activated carbon(Pd/AC)-stainless steel mesh(SS)cathode(PACSS)was proposed,which enables more efficie nt H_(2)O_(2)generation.It utilizes AC,the support of Pd catalyst,as part of cathode for H_(2)O_(2) generation via 2-electron anodic O_(2) reduction,and SS serve as a current distributor.Moreover,H_(2)O_(2) could be catalytically decomposed upon AC to generate highly reactive·OH,which avoids the use of Fe;.Compared with conventional Pd catalyst,H_(2)O_(2) concentration obtained by PACSS cathode is248.2%higher,the O_(2)utilization efficiency was also increased from 3.2%to 10.8%.Within 50 min,26.3%,72.5%,and 94.0%H_(2)O_(2) was decomposed by Pd,AC,and Pd/AC.Fluorescence detection results implied that Pd/AC is effective upon H_(2)O_(2) activation for·OH generation.Finally,iron-free EF process enabled by PACSS cathode was examined to be effective for reactive blue 19(RB19)degradation.After continuous running for 10 cycles(500 min),the PACSS cathode was still stable for H_(2)O_(2)generation,H_(2)O_(2)activation,and RB19 degradation,showing its potential application for organic pollutants degradation without increase in the running cost.展开更多
The aim of this paper is to understand the common characteristics of the generalized flyby trajectory around natural elongated bodies. Such flyby trajectories provide a short-term mechanism to clear away vicinal objec...The aim of this paper is to understand the common characteristics of the generalized flyby trajectory around natural elongated bodies. Such flyby trajectories provide a short-term mechanism to clear away vicinal objects or temporally capture ejecta into circling orbits. The gravitational potential of elongated bodies is described by a unified approximate model, i.e., the rotating mass dipole which is two point masses connected with a constant massless rod The energy power is used to illustrate the flyby effect in terms of the instantaneous orbital energy. The essential of the single flyby trajectory is studied analytically, and the relationship between the flyby trajectory and its Jacobi integral is also illustrated. Sample trajectories are given to show the variational trend of the energy increment with respect to differen orbital periapsides. The distribution of natural ejecting orbits is presented by varying the parameters of the approximate model.展开更多
The United Nations Framework Convention on Climate Change(UNFCCC)has established a climate governance mechanism with intergovernmental negotiations among sovereign states as the core.After nearly 30 years,progress in ...The United Nations Framework Convention on Climate Change(UNFCCC)has established a climate governance mechanism with intergovernmental negotiations among sovereign states as the core.After nearly 30 years,progress in combating climate change has remained very modest compared with the numerous challenges raised.The global climate governance has entered a new era,such that incorporating other factors into the governance process is timely.Therefore,the study emphasizes technological innovation and business actors in climate governance after the Paris Agreement.Technological innovation can provide effective solutions for combating climate change and has been a crucial driving force in climate governance's evolution.Business actors are significant because they are actual implementers of technological innovation and can apply different types of power and influence on climate governance processes at various levels.In summary,business actors,as well as technological innovation in line with governments and the UNFCCC governance frameworks,create a new potential for climate governance in the new era.展开更多
A pre-ohmic micro-patterned recess process,is utilized to fabricate Ti/Al/Ti/TiN ohmic contact to an ultrathin-barrier(UTB)AlGaN/GaN heterostructure,featuring a significantly reduced ohmic contact resistivity of 0.56...A pre-ohmic micro-patterned recess process,is utilized to fabricate Ti/Al/Ti/TiN ohmic contact to an ultrathin-barrier(UTB)AlGaN/GaN heterostructure,featuring a significantly reduced ohmic contact resistivity of 0.56Ω·mm at an alloy temperature of 550℃.The sheet resistances increase with the temperature following a power law with the index of +2.58,while the specific contact resistivity decreases with the temperature.The contact mechanism can be well described by thermionic field emission(TFE).The extracted Schottky barrier height and electron concentration are 0.31 eV and 5.52×10^(18) cm^(−3),which suggests an intimate contact between ohmic metal and the UTB-AlGaN as well as GaN buffer.A good correlation between ohmic transfer length and the micro-pattern size is revealed,though in-depth investigation is needed.A preliminary CMOS-process-compatible metal-insulator-semiconductor high-mobility transistor(MIS-HEMT)was fabricated with the proposed Au-free ohmic contact technique.展开更多
Recently,Coordination Polymers(CPs)have been widely utilized as energy storage materials for reversible Lithium-Ion Batteries(LIBs)benefiting from their tunable building blocks and adjusted electrochemical properties....Recently,Coordination Polymers(CPs)have been widely utilized as energy storage materials for reversible Lithium-Ion Batteries(LIBs)benefiting from their tunable building blocks and adjusted electrochemical properties.However,the unsatisfied electrochemical behavior of CPs with poor conductivity and sluggish ion transport kinetics is still a bottle-neck for their large-scale energy storage applications in LIBs.Herein,we display the rational fabrication of a conductive Sn-based coordination polymer(Sn-DHTPA)via judiciously choosing suitable building units.The Sn-DHTPA is employed as anode for LIBs,exhibiting superior reversible storage capacity of 1142.6 m A h g^(-1) at 0.1 A g^(-1) after 100 cycles and impressive rate storage capability of 287.7 m A h g^(-1)at 20 A g^(-1).More importantly,a robust cycling performance of 205.5 m A h g^(-1) at an extra-high current density of 20 A g^(-1) are observed without remarkable capacity-fading up to1000 cycles.The behavior superiority of Sn-DHTPA is related to its advanced architecture with abundant lithium storage sites,high electrical conductivity and rapid lithium transport.A series of ex-situ characterizations reveal that the impressive lithium storage capacity is contributed by the redox active sites of both the aromatic linker and metal center related to in-situ generated metallic nanoparticles dispersed in the skeleton.展开更多
The d-band centers of catalysts have exhibited excellent performance in various reactions.Among them,the enhanced catalytic reaction is considered a crucial way to power dynamics and reduce the“shuttle”effect in pol...The d-band centers of catalysts have exhibited excellent performance in various reactions.Among them,the enhanced catalytic reaction is considered a crucial way to power dynamics and reduce the“shuttle”effect in polysulfide conversions of lithium-sulfur batteries.Here,we report two-dimensional-shaped tungsten borides(WB)nanosheets with d-band centers,where the d orbits of W atoms on the(001)facets show greatly promoting the electrocatalytic sulfur reduction reaction.As-prepared WB-based Li-S cells exhibit excellent electrochemical performance for Li-ion storage.Especially,it delivers superior capacities of 7.7 mAh/cm^(2) under the 8.0 mg/cm^(2) sulfur loading,which is far superior to most other electrode catalysts.This study provides insights into the d-band centers as a promising catalyst of twodimensional boride materials.展开更多
In this study,various conditions for the removal of polyvinyl alcohol(PVA)by electrocoagulation(EC)coupled catalytic oxidation are systematically studied.The direct oxidation of the anode,the reduction of the cathode,...In this study,various conditions for the removal of polyvinyl alcohol(PVA)by electrocoagulation(EC)coupled catalytic oxidation are systematically studied.The direct oxidation of the anode,the reduction of the cathode,the oxidation of·OH and·Cl,and the synergistic effect of flocculation on the degradation of polyvinyl alcohol are investigated.It is observed that the optimum experimental conditions obtained are as follows:Cell voltage 9 V,natural pH 7,NaCl concentration 0.02 mol/L,and interelectrode distance3.0 cm.The evolution of iron ions is also discussed in the EC process.By contrast,EC had made an outstanding contribution to the removal of PVA,which removes 71.29%of PVA.Free radicals,especially·OH and·Cl,are equivalent to the contribution of the electrodes in the degradation of PVA.And the contribution of PVA degradation by anode oxidation and cathode reduction are 12.76%and 8.02%,respectively.Characterization of solution and floc,such as Fourier transform infrared spectrometry(FTIR),scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDS),thermogravimetric analysis(TGA),GC-MS and molecular weight,showed that PVA is effectively removed by the EC process,and a possible degradation pathway is proposed.展开更多
This paper examined how microstructure influences the homogenized thermal conductivity of cellular structures and revealed a surface-induced size-dependent effect.This effect is linked to the porous microstructural fe...This paper examined how microstructure influences the homogenized thermal conductivity of cellular structures and revealed a surface-induced size-dependent effect.This effect is linked to the porous microstructural features of cellular structures,which stems from the degree of porosity and the distri-bution of the pores.Unlike the phonon-driven surface effect at the nanoscale,the macro-scale surface mechanism in thermal cellular structures is found to be the microstructure-induced changes in the heat conduction path based on fully resolved 3D numerical simulations.The surface region is determined by the microstructure,characterized by the intrinsic length.With the coupling between extrinsic and intrinsic length scales under the surface mechanism,a surface-enriched multiscale method was devel-oped to accurately capture the complex size-dependent thermal conductivity.The principle of scale separation required by classical multiscale methods is not necessary to be satisfied by the proposed multiscale method.The significant potential of the surface-enriched multiscale method was demon-strated through simulations of the effective thermal conductivity of a thin-walled metamaterial struc-ture.The surface-enriched multiscale method offers higher accuracy compared with the classical multiscale method and superior efficiency over high-fidelity finite element methods.展开更多
Based on Multi-Masking Empirical Mode Decomposition (MMEMD) and fuzzy c-means (FCM) clustering, a new method of wind turbine bearing fault diagnosis FCM-MMEMD is proposed, which can determine the fault accurately and ...Based on Multi-Masking Empirical Mode Decomposition (MMEMD) and fuzzy c-means (FCM) clustering, a new method of wind turbine bearing fault diagnosis FCM-MMEMD is proposed, which can determine the fault accurately and timely. First, FCM clustering is employed to classify the data into different clusters, which helps to estimate whether there is a fault and how many fault types there are. If fault signals exist, the fault vibration signals are then demodulated and decomposed into different frequency bands by MMEMD in order to be analyzed further. In order to overcome the mode mixing defect of empirical mode decomposition (EMD), a novel method called MMEMD is proposed. It is an improvement to masking empirical mode decomposition (MEMD). By adding multi-masking signals to the signals to be decomposed in different levels, it can restrain low-frequency components from mixing in highfrequency components effectively in the sifting process and then suppress the mode mixing. It has the advantages of easy implementation and strong ability of suppressing modal mixing. The fault type is determined by Hilbert envelope finally. The results of simulation signal decomposition showed the high performance of MMEMD. Experiments of bearing fault diagnosis in wind turbine bearing fault diagnosis proved the validity and high accuracy of the new method.展开更多
This paper proposes an optimal,robust,and efficient guidance scheme for the perturbed minimum-time low-thrust transfer toward the geostationary orbit.The Earth’s oblateness perturbation and shadow are taken into acco...This paper proposes an optimal,robust,and efficient guidance scheme for the perturbed minimum-time low-thrust transfer toward the geostationary orbit.The Earth’s oblateness perturbation and shadow are taken into account.It is difficult for a Lyapunov-based or trajectory-tracking guidance method to possess multiple characteristics at the same time,including high guidance optimality,robustness,and onboard computational efficiency.In this work,a concise relationship between the minimum-time transfer problem with orbital averaging and its optimal solution is identified,which reveals that the five averaged initial costates that dominate the optimal thrust direction can be approximately determined by only four initial modified equinoctial orbit elements after a coordinate transformation.Based on this relationship,the optimal averaged trajectories constituting the training dataset are randomly generated around a nominal averaged trajectory.Five polynomial regression models are trained on the training dataset and are regarded as the costate estimators.In the transfer,the spacecraft can obtain the real-time approximate optimal thrust direction by combining the costate estimations provided by the estimators with the current state at any time.Moreover,all these computations onboard are analytical.The simulation results show that the proposed guidance scheme possesses extremely high guidance optimality,robustness,and onboard computational efficiency.展开更多
As an emerging star in the family of two-dimensional(2D)materials,2D transition metal carbides,carbonitrides and nitrides,collectively referred to as MXenes,have large specific surface area,rich active sites,metallic ...As an emerging star in the family of two-dimensional(2D)materials,2D transition metal carbides,carbonitrides and nitrides,collectively referred to as MXenes,have large specific surface area,rich active sites,metallic conductivity and adjustable surface chemical properties.These features make MXenes promising candidates for gas-sensing materials.For the past few years,MXene-based sensors have drawn increasing attention due to their enhanced sensor performance.Based on this,this review systematically represents the structure,synthesis methods and properties of MXenes,and summarizes their applications in gas sensors.Firstly,the types,structure,main synthesis methods and properties of MXenes are introduced in a comprehensive way.Next,the corresponding design principle and working mechanism of MXene-based gas sensor are clarified.Subsequently,the sensing performances of pristine MXenes and the MXene-based nanocomposite are discussed.Finally,some future opportunities and challenges of MXene-based sensors are pointed out.展开更多
基金National Natural Science Foundation of China(No.52476192,No.52106237)Natural Science Foundation of Heilongjiang Province(No.YQ2022E027)。
文摘The transition of hydrogen sourcing from carbon-intensive to water-based methodologies is underway,with renewable energy-powered proton exchange membrane water electrolysis(PEMWE)emerging as the preeminent pathway for hydrogen production.Despite remarkable advancements in this field,confronting the sluggish electrochemical kinetics and inherent high-energy consumption arising from deteriorated mass transport within PEMWE systems remains a formidable obstacle.This impediment stems primarily from the hindered protons mass transfer and the untimely hydrogen bubbles detachment.To address these challenges,we harness the inherent variability of electrical energy and introduce an innovative pulsed dynamic water electrolysis system.Compared to constant voltage electrolysis(hydrogen production rate:51.6 m L h^(-1),energy consumption:5.37 kWh Nm-^(3)H_(2)),this strategy(hydrogen production rate:66 m L h^(-1),energy consumption:3.83 kWh Nm-^(3)H_(2))increases the hydrogen production rate by approximately 27%and reduces the energy consumption by about 28%.Furthermore,we demonstrate the practicality of this system by integrating it with an off-grid photovoltaic(PV)system designed for outdoor operation,successfully driving a hydrogen production current of up to 500 mA under an average voltage of approximately 2 V.The combined results of in-situ characterization and finite element analysis reveal the performance enhancement mechanism:pulsed dynamic electrolysis(PDE)dramatically accelerates the enrichment of protons at the electrode/solution interface and facilitates the release of bubbles on the electrode surface.As such,PDE-enhanced PEMWE represents a synergistic advancement,concurrently enhancing both the hydrogen generation reaction and associated transport processes.This promising technology not only redefines the landscape of electrolysis-based hydrogen production but also holds immense potential for broadening its application across a diverse spectrum of electrocatalytic endeavors.
基金supported by a project of the Tsinghua Shenzhen International Graduate School-Shenzhen Pengrui Young Faculty Program of Shenzhen Pengrui Foundation(Grant No.SZPR2023007)Natural Science Foundation of Sichuan Province(Grant No.2025ZNSFSC0449)Shenzhen Science and Technology Program(Grant No.RCBS20231211090637065).
文摘Lithium-ion batteries with LiCoO_(2)(LCO)cathodes are widely used in various electronic devices,resulting in a large amount of spent LCO(SLCO).Therefore,there is an urgent need for an efficient technique for recycling SLCO.However,due to the presence of cobalt oxide with a spinel phase on the surface of highly-degraded LCO,the strong electrostatic repulsion from the transition metal octahedron poses a high Li replenishment barrier,making the regeneration of highly-degraded LCO a challenge.Herein,we propose a structural transformation strategy for reconstructing Li replenishment channels to aid the direct regeneration of highly-degraded LCO.In this approach,ball milling is employed to disrupt the inherent structure of highly-degraded LCO,thereby releasing the internal stress and converting the surface spinel phase into a homogeneous amorphous structure,which promotes Li insertion and regeneration.The regenerated LCO(RLCO)exhibits an outstanding discharge capacity of 179.10 mAh·g^(−1) in the voltage range of 3.0–4.5 V at 0.5 C.The proposed strategy is an effective regeneration approach for highly-degraded LCO,thereby facilitating the efficient recycling of spent lithium-ion battery cathode materials.
基金supported by the National Key Research and Development Program of China(No.2021YFB3701303)Foundation Strengthening Plan Technical Field Fund(No.2021-JJ-0112)+1 种基金Major Scientific and Technological Innovation Project of Luoyang(No.2201029A)National Natural Science Foundation of China(No.U2037601).
文摘The ultra-light Mg–8Li–3Al–2Zn–0.5Y(LAZ832–0.5Y)thin wall parts with excellent performances were successfully fabricated by Gas Tungsten Arc Welding(GTAW)in this study.The microstructure of the top,middle and bottom regions of the thin wall fabricated under various conditions was examined and the mechanical properties of these thin walls were tested.The results showed that much finer microstructure was obtained by GTAW than that made by conventional casting method.In the as-deposited samples,the needle-like shapedα-Mg phase emerged at the top of the thin wall whereas the bar-shapedα-Mg phase showed up in the middle and bottom regions of the thin wall due to the complex thermal history.The Al2Y phase was dispersed throughout bothα-Mg andβ-Li while the AlLi phase was mainly located in theβ-Li.The best combination of ultimate tensile strength(UTS),yield strength(YS)and elongation to fracture of the as-deposited thin wall were 218.9 MPa,171.4 MPa and 20.9%,respectively,which was manufactured under the optimal condition of 120 A 1800 mm/min 220 mm/min.After solid solution treatment at 350℃for 4 h,the UTS increased slightly by 13%but the YS increased significantly by 65%compared with the samples before solid solution.The solution of the AlLi phase was believed to be the main strengthening mechanism.It is interesting to note that the UTS and YS of the as-deposited sample was better than those of the as-cast sample while the opposite situation took place after solid solution treatment.
基金the financial support from the Natural Science Foundation of Shanghai(24ZR1453900)Project for AI-Driven Reform of Research Paradigms to Empower Advancement of Disciplines(Z-2024-369-036)。
文摘Rational design of catalytic interfaces at the atomic level is crucial for enhancing electrocatalytic CO_(2)reduction.In this study,a Zeolite imidazolate frameworks-8 derived catalyst is developed,featuring atomically dispersed Ni–Zn dual-atom sites(NiZnN_(6))coexisting with Ni_(3)ZnC_(0.7) nanoparticles on nitrogen-doped carbon nanotubes.Strong interaction between the NiZnN_(6) moieties and Ni_(3)ZnC_(0.7) nanoparticle induces charge redistribution,enhancing the electron-donating ability of Ni active sites.Simultaneously,the dual-atom configuration creates an asymmetric electronic environment,where interfacial electronic coupling facilitates partial electron transfer from Zn to Ni,leading to electron enrichment at the Ni center.Consequently,Ni sites preferentially donate electrons to active CO_(2)molecules,lowering the ^(*)COOH formation energy,while Zn sites promote ^(*)CO desorption,thus achieving high CO selectivity(99.6%@-0.7V vs.Reversible Hydrogen Electrode(RHE)).The in-depth investigation in this work provides guidance for establishing the relationship between structure and electrocatalytic activity,holding significant implications for fundamental research on the CO_(2)reduction mechanism.
文摘Soil water-stable aggregates (WSAs) are the basic unit of soil constitution and can contribute to remaining the stable soil constitution. The objective of this study was to clarify the distribution and stability of WSAs and the soil organic carbon (SOC), the total nitrogen (TN), and the total phosphorus (TP) concentrations in 0 - 20 cm and 20 - 40 cm soil layers under the different ages of Robinia pseudoacacia plantations. The 20, 25, 40, and 50 years-old Robinia pseudoacacia plantations were selected. Stepwise regression analysis showed that >5 mm and 1 - 2 mm WSAs, SOC concentration in 2 - 5 mm WSAs, and TN and TP concentrations in < 0.25 mm WSAs were dominant independent variables affecting aggregate stability and that SOC in 0.25 - 0.5 mm WSAs, TN in <0.25 mm and 1 - 2 mm WSAs and TP in 2 - 5 mm WSAs were dominant independent variables affecting SOC, TN, and TP concentrations in bulk soils.
基金This study was funded by the Science and Technology Development Fund,Macao SAR(File no.0191/2017/A3,0041/2019/A1,0046/2019/AFJ,0021/2019/AIR)the University of Macao(File no.MYRG2017-00216-FST and MYRG2018-00192-IAPME)+2 种基金the UEA funding,Science and Technology Program of Guangzhou(2019050001)the National Key Research and Development Program of China(2019YFE0198000)Fuming Chen acknowledges the Pearl River Talent Program(2019QN01L951).
文摘Aluminum-metal batteries show great potential as next-generation energy storage due to their abundant resources and intrinsic safety.However,the crucial limitations of metallic Al anodes,such as dendrite and corrosion problems in conventional aluminum-metal batteries,remain challenging and elusive.Here,we report a novel electrodeposition strategy to prepare an optimized 3D Al anode on carbon cloth with an uniform deposition morphology,low local current density,and mitigatory volume change.The symmetrical cells with the 3D Al anode show superior stable cycling(>450 h)and low-voltage hysteresis(~170 mV)at 0.5 mA cm^(−2).High reversibility(~99.7%)is achieved for the Al plating/stripping.The graphite||Al‐4/CC full batteries show a long lifespan of 800 cycles with 54 mAh g^(−1) capacity at a high current density of 1000 mA g^(−1),benefiting from the high capacitive-controlled distribution.This study proposes a novel strategy to design 3D Al anodes for metallic-Al-based batteries by eliminating the problems of planar Al anodes and realizing the potential applications of aluminum-graphite batteries.
基金NSFC(Nos.U22A20403,21301151 and 52070115)Natural Science Foundation of Hebei Province(Nos.B2021203036 and E2022203011)Key Project of the Hebei Education Department(No.ZD2021103).
文摘Polystyrene resins(PS)have been practical ion exchangers for radionuclides removal from water.However,nonspecific effects of ion exchange groups continue to be a major obstacle for emergency treatment with coexisting ions of high concentrations.The selectivity for Cs+enables zirconium phosphate(ZrP)to be the most promising inorganic sorbent for radioactive cesium extraction,despite being difficult to synthesize and causing excessive pressure loss in fixed-bed reactors due to fine powder.Herein,through facile confined crystallization in host macropores,we prepared PS confinedα-ZrP nanocrystalline(ZrP-PS).Size-screen sorption of layeredα-ZrP and sulfonic acid group preconcentration of PS synergistically enable a considerably higher Cs+affinity of ZrP-PS than PS,as confirmed by X-ray photoelectron spectroscopy(XPS)analysis.ZrP-PS demonstrated remarkable cesium sequestration performance in both batch and continuous experiments,with a high adsorption capacity of 269.58 mg/g,a rapid equilibrium within 80 min,and a continuous effluent volume of 2300 L/kg sorbents.Given the excellent selectivity for Cs+and flexibility to separate from treated water,ZrP-PS holds great promise as purification packages for the emergency treatment of radioactively contaminated water.
基金financially supported by National Natural Science Foundation of China(Grant Nos.51972070 and 52062004)Guizhou Provincial High Level Innovative Talents Project(Grant No.QKHPTRC-GCC[2022]013-1)+2 种基金Innovation Team for Advanced Electrochemical Energy Storage Devices and Key Materials of Guizhou Provincial Higher Education Institutions(Grant No.QianJiaoJi[2023]054)Guizhou Provincial Science and Technology Projects(Grant No.QKHJC[2020]1Z042)Cultivation Project of Guizhou University(Grant No.GDPY[2019]01)。
文摘The“shuttle effect”of lithium polysulfides(LiPSs)is a huge challenge for practical use of high-energydensity lithium-sulfur(Li-S)batteries,and one of the main reasons is the sluggish kinetics of sulfur conversion.Metal oxides are able to expedite the sulfur electrochemistry,and the structural defects enhance the adsorption-conversion ability of metal oxides for polysulfides.However,a significant research gap still remains regarding the relationship between the oxygen vacancy concentration and the adsorptivecatalytic performance of metal oxides.Herein,we establish a correlation between oxygen vacancy concentration and adsorptive-catalytic properties by using tungsten oxide(WO_(x))as model catalysts.It is revealed that high-concentration oxygen vacancy is beneficial for enhancing the binding between tungsten oxide and LiPSs,reducing the energy barrier of Li_(2)S decomposition,and promoting polysulfide conversion kinetics.Consequently,the Li-S batteries using the tungsten oxide with high-concentration oxygen vacancies deliver high initial discharge capacity of 1169 mA h g^(-1)at 0.2 C and 865 mA h g^(-1)at 2 C,low attenuation rate of 0.064%per cycle over 1100 cycles at 2 C.With a high sulfur area loading of 5.34 mg cm^(-2),the Li-S batteries still exhibit high initial gravimetric capacity of 982 mA h g^(-1)at 0.1 C and areal capacity of 5.92 mA h cm^(-2).This work promotes the feasibility of defect engineering on metal oxides as an effective mean to enhance the practicality of Li-S batteries.
基金financially supported by the National Natural Science Foundation of China(Nos.52006049,51776055)the China Postdoctoral Science Foundation(Nos.2019M661293,2020T130149)。
文摘The Electro-Fenton(EF)process is one of the promising advanced oxidation processes(AOPs)for environmental remediation.The H_(2)O_(2) yield of EF process largely determines its performance on organic pollutants degradation.Conventional Pd-catalytic EF process generates H_(2)O_(2) via the combination reaction of anodic O_(2) and cathodic H;.However,the relatively expensive catalyst limits its application.Herein,a hybrid Pd/activated carbon(Pd/AC)-stainless steel mesh(SS)cathode(PACSS)was proposed,which enables more efficie nt H_(2)O_(2)generation.It utilizes AC,the support of Pd catalyst,as part of cathode for H_(2)O_(2) generation via 2-electron anodic O_(2) reduction,and SS serve as a current distributor.Moreover,H_(2)O_(2) could be catalytically decomposed upon AC to generate highly reactive·OH,which avoids the use of Fe;.Compared with conventional Pd catalyst,H_(2)O_(2) concentration obtained by PACSS cathode is248.2%higher,the O_(2)utilization efficiency was also increased from 3.2%to 10.8%.Within 50 min,26.3%,72.5%,and 94.0%H_(2)O_(2) was decomposed by Pd,AC,and Pd/AC.Fluorescence detection results implied that Pd/AC is effective upon H_(2)O_(2) activation for·OH generation.Finally,iron-free EF process enabled by PACSS cathode was examined to be effective for reactive blue 19(RB19)degradation.After continuous running for 10 cycles(500 min),the PACSS cathode was still stable for H_(2)O_(2)generation,H_(2)O_(2)activation,and RB19 degradation,showing its potential application for organic pollutants degradation without increase in the running cost.
基金supported by the National Basic Research Program of China(973 Program),(Grant 2012CB720000)China Postdoctoral Science Foundation(Grant 2014M560076)Support from Shanghai Satellite Engineering Research Institute(Grant 13dz2260100)is also acknowledged
文摘The aim of this paper is to understand the common characteristics of the generalized flyby trajectory around natural elongated bodies. Such flyby trajectories provide a short-term mechanism to clear away vicinal objects or temporally capture ejecta into circling orbits. The gravitational potential of elongated bodies is described by a unified approximate model, i.e., the rotating mass dipole which is two point masses connected with a constant massless rod The energy power is used to illustrate the flyby effect in terms of the instantaneous orbital energy. The essential of the single flyby trajectory is studied analytically, and the relationship between the flyby trajectory and its Jacobi integral is also illustrated. Sample trajectories are given to show the variational trend of the energy increment with respect to differen orbital periapsides. The distribution of natural ejecting orbits is presented by varying the parameters of the approximate model.
文摘The United Nations Framework Convention on Climate Change(UNFCCC)has established a climate governance mechanism with intergovernmental negotiations among sovereign states as the core.After nearly 30 years,progress in combating climate change has remained very modest compared with the numerous challenges raised.The global climate governance has entered a new era,such that incorporating other factors into the governance process is timely.Therefore,the study emphasizes technological innovation and business actors in climate governance after the Paris Agreement.Technological innovation can provide effective solutions for combating climate change and has been a crucial driving force in climate governance's evolution.Business actors are significant because they are actual implementers of technological innovation and can apply different types of power and influence on climate governance processes at various levels.In summary,business actors,as well as technological innovation in line with governments and the UNFCCC governance frameworks,create a new potential for climate governance in the new era.
基金supported by National Natural Science Foundation of China under Grant 61822407,Grant 62074161,and Grant 11634002in part by the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(CAS)under Grant QYZDB-SSW-JSC012+3 种基金in part by the National Key Research and Development Program of China under Grant 2016YFB0400105 and Grant 2017YFB0403000in part by the Youth Innovation Promotion Association of CASin part by the University of Chinese Academy of Sciencesand in part by the Opening Project of Key Laboratory of Microelectronic Devices&Integrated Technology,Institute of Microelectronics,CAS.
文摘A pre-ohmic micro-patterned recess process,is utilized to fabricate Ti/Al/Ti/TiN ohmic contact to an ultrathin-barrier(UTB)AlGaN/GaN heterostructure,featuring a significantly reduced ohmic contact resistivity of 0.56Ω·mm at an alloy temperature of 550℃.The sheet resistances increase with the temperature following a power law with the index of +2.58,while the specific contact resistivity decreases with the temperature.The contact mechanism can be well described by thermionic field emission(TFE).The extracted Schottky barrier height and electron concentration are 0.31 eV and 5.52×10^(18) cm^(−3),which suggests an intimate contact between ohmic metal and the UTB-AlGaN as well as GaN buffer.A good correlation between ohmic transfer length and the micro-pattern size is revealed,though in-depth investigation is needed.A preliminary CMOS-process-compatible metal-insulator-semiconductor high-mobility transistor(MIS-HEMT)was fabricated with the proposed Au-free ohmic contact technique.
基金financially supported by National Natural Science Foundation of China(51702056)Fundamental Research Funds for the Central Universities(2162140621617330)+2 种基金Science and Technology Program of Guangzhou(202102020737,201605030008)Provincial Natural Science Foundation of Anhui(1908085ME120)Primary Research and Development Program of Anhui Province(201904a05020087)。
文摘Recently,Coordination Polymers(CPs)have been widely utilized as energy storage materials for reversible Lithium-Ion Batteries(LIBs)benefiting from their tunable building blocks and adjusted electrochemical properties.However,the unsatisfied electrochemical behavior of CPs with poor conductivity and sluggish ion transport kinetics is still a bottle-neck for their large-scale energy storage applications in LIBs.Herein,we display the rational fabrication of a conductive Sn-based coordination polymer(Sn-DHTPA)via judiciously choosing suitable building units.The Sn-DHTPA is employed as anode for LIBs,exhibiting superior reversible storage capacity of 1142.6 m A h g^(-1) at 0.1 A g^(-1) after 100 cycles and impressive rate storage capability of 287.7 m A h g^(-1)at 20 A g^(-1).More importantly,a robust cycling performance of 205.5 m A h g^(-1) at an extra-high current density of 20 A g^(-1) are observed without remarkable capacity-fading up to1000 cycles.The behavior superiority of Sn-DHTPA is related to its advanced architecture with abundant lithium storage sites,high electrical conductivity and rapid lithium transport.A series of ex-situ characterizations reveal that the impressive lithium storage capacity is contributed by the redox active sites of both the aromatic linker and metal center related to in-situ generated metallic nanoparticles dispersed in the skeleton.
基金supported by the National Natural Science Foundation of China(Nos.61904080,22205101)the Natural Science Foundation of Jiangsu Province(No.BK20190670)+5 种基金the Natural Science Foundation of Colleges and Universities in Jiangsu Province(No.19KJB530008)the Macao Young Scholars Program(No.AM2020005)the High-Performance Computing Cluster(HPCC)of Information and Communication Technology Office(ICTO)at University of Macao,Science and Technology Development Fund,Macao SAR(Nos.0191/2017/A3,0041/2019/A1,0046/2019/AFJ,0021/2019/AIR)University of Macao(Nos.MYRG2017-00216-FST and MYRG2018-00192-IAPME),FDCT Funding Scheme for Postdoctoral Researchers(No.0026/APD/2021)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)the UEA funding,and Guangdong Basic and Applied Basic Research Foundation(No.2022A1515110994).
文摘The d-band centers of catalysts have exhibited excellent performance in various reactions.Among them,the enhanced catalytic reaction is considered a crucial way to power dynamics and reduce the“shuttle”effect in polysulfide conversions of lithium-sulfur batteries.Here,we report two-dimensional-shaped tungsten borides(WB)nanosheets with d-band centers,where the d orbits of W atoms on the(001)facets show greatly promoting the electrocatalytic sulfur reduction reaction.As-prepared WB-based Li-S cells exhibit excellent electrochemical performance for Li-ion storage.Especially,it delivers superior capacities of 7.7 mAh/cm^(2) under the 8.0 mg/cm^(2) sulfur loading,which is far superior to most other electrode catalysts.This study provides insights into the d-band centers as a promising catalyst of twodimensional boride materials.
基金the National Natural Science Foundation of China(No.21906011)the Postdoctoral Science Foundation of China(No.2018M643412)。
文摘In this study,various conditions for the removal of polyvinyl alcohol(PVA)by electrocoagulation(EC)coupled catalytic oxidation are systematically studied.The direct oxidation of the anode,the reduction of the cathode,the oxidation of·OH and·Cl,and the synergistic effect of flocculation on the degradation of polyvinyl alcohol are investigated.It is observed that the optimum experimental conditions obtained are as follows:Cell voltage 9 V,natural pH 7,NaCl concentration 0.02 mol/L,and interelectrode distance3.0 cm.The evolution of iron ions is also discussed in the EC process.By contrast,EC had made an outstanding contribution to the removal of PVA,which removes 71.29%of PVA.Free radicals,especially·OH and·Cl,are equivalent to the contribution of the electrodes in the degradation of PVA.And the contribution of PVA degradation by anode oxidation and cathode reduction are 12.76%and 8.02%,respectively.Characterization of solution and floc,such as Fourier transform infrared spectrometry(FTIR),scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDS),thermogravimetric analysis(TGA),GC-MS and molecular weight,showed that PVA is effectively removed by the EC process,and a possible degradation pathway is proposed.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFB1714600)the National Natural Science Foundation of China(Grant No.52175095)the Young Top-Notch Talent Cultivation Program of Hubei Province of China.
文摘This paper examined how microstructure influences the homogenized thermal conductivity of cellular structures and revealed a surface-induced size-dependent effect.This effect is linked to the porous microstructural features of cellular structures,which stems from the degree of porosity and the distri-bution of the pores.Unlike the phonon-driven surface effect at the nanoscale,the macro-scale surface mechanism in thermal cellular structures is found to be the microstructure-induced changes in the heat conduction path based on fully resolved 3D numerical simulations.The surface region is determined by the microstructure,characterized by the intrinsic length.With the coupling between extrinsic and intrinsic length scales under the surface mechanism,a surface-enriched multiscale method was devel-oped to accurately capture the complex size-dependent thermal conductivity.The principle of scale separation required by classical multiscale methods is not necessary to be satisfied by the proposed multiscale method.The significant potential of the surface-enriched multiscale method was demon-strated through simulations of the effective thermal conductivity of a thin-walled metamaterial struc-ture.The surface-enriched multiscale method offers higher accuracy compared with the classical multiscale method and superior efficiency over high-fidelity finite element methods.
基金Supported by National Key R&D Projects(Grant No.2018YFB0905500)National Natural Science Foundation of China(Grant No.51875498)+1 种基金Hebei Provincial Natural Science Foundation of China(Grant Nos.E2018203439,E2018203339,F2016203496)Key Scientific Research Projects Plan of Henan Higher Education Institutions(Grant No.19B460001)
文摘Based on Multi-Masking Empirical Mode Decomposition (MMEMD) and fuzzy c-means (FCM) clustering, a new method of wind turbine bearing fault diagnosis FCM-MMEMD is proposed, which can determine the fault accurately and timely. First, FCM clustering is employed to classify the data into different clusters, which helps to estimate whether there is a fault and how many fault types there are. If fault signals exist, the fault vibration signals are then demodulated and decomposed into different frequency bands by MMEMD in order to be analyzed further. In order to overcome the mode mixing defect of empirical mode decomposition (EMD), a novel method called MMEMD is proposed. It is an improvement to masking empirical mode decomposition (MEMD). By adding multi-masking signals to the signals to be decomposed in different levels, it can restrain low-frequency components from mixing in highfrequency components effectively in the sifting process and then suppress the mode mixing. It has the advantages of easy implementation and strong ability of suppressing modal mixing. The fault type is determined by Hilbert envelope finally. The results of simulation signal decomposition showed the high performance of MMEMD. Experiments of bearing fault diagnosis in wind turbine bearing fault diagnosis proved the validity and high accuracy of the new method.
基金supported by the National Natural Science Foundation of China(No.12022214)the National Key R&D Program of China(No.2020YFC2201200)。
文摘This paper proposes an optimal,robust,and efficient guidance scheme for the perturbed minimum-time low-thrust transfer toward the geostationary orbit.The Earth’s oblateness perturbation and shadow are taken into account.It is difficult for a Lyapunov-based or trajectory-tracking guidance method to possess multiple characteristics at the same time,including high guidance optimality,robustness,and onboard computational efficiency.In this work,a concise relationship between the minimum-time transfer problem with orbital averaging and its optimal solution is identified,which reveals that the five averaged initial costates that dominate the optimal thrust direction can be approximately determined by only four initial modified equinoctial orbit elements after a coordinate transformation.Based on this relationship,the optimal averaged trajectories constituting the training dataset are randomly generated around a nominal averaged trajectory.Five polynomial regression models are trained on the training dataset and are regarded as the costate estimators.In the transfer,the spacecraft can obtain the real-time approximate optimal thrust direction by combining the costate estimations provided by the estimators with the current state at any time.Moreover,all these computations onboard are analytical.The simulation results show that the proposed guidance scheme possesses extremely high guidance optimality,robustness,and onboard computational efficiency.
基金the National Natural Science Foundation of China(No.52172094)Natural Science Foundation of Shanghai(No.21ZR1426700).
文摘As an emerging star in the family of two-dimensional(2D)materials,2D transition metal carbides,carbonitrides and nitrides,collectively referred to as MXenes,have large specific surface area,rich active sites,metallic conductivity and adjustable surface chemical properties.These features make MXenes promising candidates for gas-sensing materials.For the past few years,MXene-based sensors have drawn increasing attention due to their enhanced sensor performance.Based on this,this review systematically represents the structure,synthesis methods and properties of MXenes,and summarizes their applications in gas sensors.Firstly,the types,structure,main synthesis methods and properties of MXenes are introduced in a comprehensive way.Next,the corresponding design principle and working mechanism of MXene-based gas sensor are clarified.Subsequently,the sensing performances of pristine MXenes and the MXene-based nanocomposite are discussed.Finally,some future opportunities and challenges of MXene-based sensors are pointed out.
