An atomic layer deposition (ALD) method has been employed to synthesize Fe3O4/graphene and Ni/graphene composites. The structure and microwave absorbing properties of the as-prepared composites are investigated. The...An atomic layer deposition (ALD) method has been employed to synthesize Fe3O4/graphene and Ni/graphene composites. The structure and microwave absorbing properties of the as-prepared composites are investigated. The surfaces of graphene are densely covered by Fe3O4 or Ni nanoparticles with a narrow size distribution, and the magnetic nanoparticles are well distributed on each graphene sheet without significant conglomeration or large vacancies. The coated graphene materials exhibit remarkably improved electromagnetic (EM) absorption properties compared to the pristine graphene. The optimal reflection loss (RL) reaches -46.4 dB at 15.6 GHz with a thickness of only 1.4 mm for the Fe3O4/graphene composites obtained by applying 100 cycles of Fe2O3 deposition followed by a hydrogen reduction. The enhanced absorption ability arises from the effective impedance matching, multiple interfacial polarization and increased magnetic loss from the added magnetic constituents. Moreover, compared with other recently reported materials, the composites have a lower filling ratio and smaller coating thickness resulting in significantly increased EM absorption properties. This demonstrates that nanoscale surface modification of magnetic particles on graphene by ALD is a very promising way to design lightweight and high-efficiency microwave absorbers.展开更多
Selective hydrogenation is an important industrial catalytic process in chemical upgrading, where Pd-based catalysts are widely used because of their high hydrogenation activities. However, poor selectivity and short ...Selective hydrogenation is an important industrial catalytic process in chemical upgrading, where Pd-based catalysts are widely used because of their high hydrogenation activities. However, poor selectivity and short catalyst lifetime because of heavy coke formation have been major concerns. In this work, atomically dispersed Pd atoms were successfully synthesized on graphitic carbon nitride (g-C3N4) using atomic layer deposition. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) confirmed the dominant presence of isolated Pd atoms without Pd nanoparticle (NP) formation. During selective hydrogenation of acetylene in excess ethylene, the g-C3N4-supported Pd NP catalysts had strikingly higher ethylene selectivities than the conventional Pd/Al2O3 and Pd/SiO2 catalysts. In-situ X-ray photoemission spectroscopy revealed that the considerable charge transfer from the Pd NPs to g-C3N4 likely plays an important role in the catalytic performance enhancement. More impressively, the single-atom Pd1/C3N4 catalyst exhibited both higher ethylene selectivity and higher coking resistance. Our work demonstrates that the single-atom Pd catalyst is a promising candidate for improving both selectivity and coking-resistance in hydrogenation reactions.展开更多
Micro-arc oxidation(MAO)coating with outstanding adhesion strength to Mg alloys has attracted more and more attention.However,owing to the porous structure,aggressive ions easily invaded the MAO/substrate interface th...Micro-arc oxidation(MAO)coating with outstanding adhesion strength to Mg alloys has attracted more and more attention.However,owing to the porous structure,aggressive ions easily invaded the MAO/substrate interface through the through pores,limiting long-term corrosion resistance.Therefore,a dense and biocompatible tantalum oxide(Ta2O5)nanofilm was deposited on MAO coated Mg alloy AZ31 through atomic layer deposition(ALD)technique to seal the micropores and regulate the degradation rate.Surface micrography,chemical compositions and crystallographic structure were characterized using FE-SEM,EDS,XPS and XRD.The corrosion resistance of all samples was evaluated through electrochemical and hydrogen evolution tests.Results revealed that the Ta2O5 film mainly existed in the form of amorphousness.Moreover,uniform deposition of Ta2O5 film and effective sealing of micropores and microcracks in MAO coating were achieved.The current density(icorr)of the composite coating decreased three orders of magnitude than that of the substrate and MAO coating,improving corrosion resistance.Besides,the formation and corrosion resistance mechanisms of the composite coating were proposed.展开更多
Lithium (Li) metal has been considered as the most attractive anode materials for Li-ion batteries (LIBs) due to its high theoretic specific capacity. The formation of unstable solid electrolyte interphase (SEI)...Lithium (Li) metal has been considered as the most attractive anode materials for Li-ion batteries (LIBs) due to its high theoretic specific capacity. The formation of unstable solid electrolyte interphase (SEI) and dendritic Li on the metal anode, however, hindered its practical application. Herein, to address the issues, a Li-free electrode with ultrathin Al2O3 coated on reduced graphene oxide (rGO) membrane that covers a Cu foil current collector was developed. The composite electrode exhibits excellent interfacial protection of lithium metal deposited between Cu foil and rGO electrochemically. Firstly, it affords good Li^+ permeability from the electrolyte. Secondly, the ultrathin Al2O3 has sufficient mechanical strength to inhibit the penetration of Li dendrite. Li metal was observed uniformly deposited between rGO membrane and Cu collector, and stable cycle performance of Li plating/stripping with Coulombic efficiency of ~ 91.75% at the lOOth cycle is achieved in organic carbonate electrolyte without any additives.展开更多
Noble single‐atom catalysts have rapidly been attracting attention due to their unique catalytic properties and maximized utilization.Atomic layer deposition(ALD)is an emerging powerful technique for large‐scale syn...Noble single‐atom catalysts have rapidly been attracting attention due to their unique catalytic properties and maximized utilization.Atomic layer deposition(ALD)is an emerging powerful technique for large‐scale synthesis of stable single atom.In this review,we summarize recent developments of single atom synthesized by ALD as well as explore future research direction and trends.展开更多
Developing highly efficient magnetic microwave absorb-ers(MAs)is crucial,and yet challenging for anti-corrosion properties in extremely humid and salt-induced foggy environments.Herein,a dual-oxide shell of ZnO/Al_(2)...Developing highly efficient magnetic microwave absorb-ers(MAs)is crucial,and yet challenging for anti-corrosion properties in extremely humid and salt-induced foggy environments.Herein,a dual-oxide shell of ZnO/Al_(2)O_(3) as a robust barrier to FeSiAl core is introduced to mitigate corrosion resistance.The FeSiAl@ZnO@Al_(2)O_(3) layer by layer hybrid structure is realized with atomic-scale precision through the atomic layer deposition technique.Owing to the unique hybrid structure,the FeSiAl@ZnO@Al_(2)O_(3) exhibits record-high micro-wave absorbing performance in low-frequency bands covering L and S bands with a minimum reflection loss(RLmin)of-50.6 dB at 3.4 GHz.Compared with pure FeSiAl(RLmin of-13.5 dB,a bandwidth of 0.5 GHz),the RLmin value and effective bandwidth of this designed novel absorber increased up to~3.7 and~3 times,respectively.Fur-thermore,the inert ceramic dual-shells have improved 9.0 times the anti-corrosion property of FeSiAl core by multistage barriers towards corrosive medium and obstruction of the electric circuit.This is attributed to the large charge transfer resistance,increased impedance modulus|Z|0.01 Hz,and frequency time constant of FeSiAl@ZnO@Al_(2)O_(3).The research demonstrates a promising platform toward the design of next-generation MAs with improved anti-corrosion properties.展开更多
Electrocatalysis is a promising approach to clean energy conversion due to its high efficiency and low environmental pollution. Noble metal materials have been studied to show high activity toward electrocatalyltic re...Electrocatalysis is a promising approach to clean energy conversion due to its high efficiency and low environmental pollution. Noble metal materials have been studied to show high activity toward electrocatalyltic reactions, although such applications remain restricted by the high cost and poor durability of the noble metals. By precisely adjusting the catalyst composition, size, and structure, electrocatalysts with excellent performance can be obtained. Atomic layer deposition(ALD) is a technique used to produce ultrathin films and ultrafine nanoparticles at the atomic level. It possesses unique advantages for the controllable design and synthesis of electrocatalysts. Furthermore, the homogenous composition and structure of the electrocatalysts prepared by ALD favor the exploration of structure-reactivity relationships and catalytic mechanisms. In this review, the mechanism, characteristics, and advantages of ALD in fabricating nanostructures are introduced first. Subsequently, the problems associated with existing electrocatalysts and a series of recently developed ALD strategies to enhance the activity and durability of electrocatalysts are presented. For example, the deposition of ultrafine Pt nanoparticles to increase the utilization and activity of Pt, fabrication of core–shell, overcoat, nanotrap, and other novel structures to protect the noble-metal nanoparticles and enhance the catalyst stability. In addition, ALD developments in synthesizing non-noble metallic electrocatalysts are summarized and discussed. Finally, based on the current studies, an outlook for the ALD application in the design and synthesis of electrocatalysts is presented.展开更多
Developing advanced technologies to stabilize positive electrodes of lithium ion batteries under high-voltage operation is becoming increasingly important,owing to the potential to achieve substantially enhanced energ...Developing advanced technologies to stabilize positive electrodes of lithium ion batteries under high-voltage operation is becoming increasingly important,owing to the potential to achieve substantially enhanced energy density for applications such as portable electronics and electrical vehicles.Here,we deposited chemically inert and ionically conductive LiAlO2 interfacial layers on LiCoO2 electrodes using the atomic layer deposition technique.During prolonged cycling at high-voltage,the LiAlO2 coating not only prevented interfacial reactions between the LiCoO2 electrode and electrolyte,as confirmed by electrochemical impedance spectroscopy and Raman characterizations,but also allowed lithium ions to freely diffuse into LiCoO2 without sacrificing the power density.As a result,a capacity value close to 200 mA·h·g-1 was achieved for the LiCoO2 electrodes with commercial level loading densities,cycled at the cut-off potential of 4.6 V vs.Li+/Li for 50 stable cycles;this represents a 40% capacity gain,compared with the values obtained for commercial samples cycled at the cut-off potential of 4.2 V vs.Li+/Li.展开更多
Impedance matching is important for achieving high-efficiency microwave absorbers. The high conductivity of dielectric loss materials such as pure metals and carbon nanomaterials generally results in poor absorption o...Impedance matching is important for achieving high-efficiency microwave absorbers. The high conductivity of dielectric loss materials such as pure metals and carbon nanomaterials generally results in poor absorption owing to the low impedance matching between the absorbers and air. Carbon nanostructures are very promising candidates for high-efficiency absorption because of their attractive features including low density, high surface area, and good stability. Herein, a new strategy is proposed to improve the impedance matching of dielectric loss materials using electrospun carbon nanofibers as an example. The carbon nanofibers are coated with specifically designed gradient multilayer nanofilms with gradually increasing electroconductibility synthesized by doping ZnO with different A1203 content (AZO) by atomic layer deposition. The gradient nanofilms are composed of five layers of dielectric films, namely, pure A1203, AZO (5:1, the pulse cycle ratio of ZnO to A1203), pure ZnO, AZO (10:1), and AZO (20:1). The versatile gradient films serve as intermediate layers to tune the impedance matching between air and the carbon nanofiber surfaces. Therefore, the carbon nanofibers coated with gradient films of rationally selected thicknesses exhibit remarkably enhanced microwave absorption performance, and the optimal reflection loss reaches -58.5 dB at 16.2 GHz with a thickness of only 1.8 mm. This work can help further understand the contribution of impedance matching to microwave absorption. Our strategy is general and can be applied to improve the absorption properties of other dielectric loss materials and even for applications in other fields.展开更多
文摘An atomic layer deposition (ALD) method has been employed to synthesize Fe3O4/graphene and Ni/graphene composites. The structure and microwave absorbing properties of the as-prepared composites are investigated. The surfaces of graphene are densely covered by Fe3O4 or Ni nanoparticles with a narrow size distribution, and the magnetic nanoparticles are well distributed on each graphene sheet without significant conglomeration or large vacancies. The coated graphene materials exhibit remarkably improved electromagnetic (EM) absorption properties compared to the pristine graphene. The optimal reflection loss (RL) reaches -46.4 dB at 15.6 GHz with a thickness of only 1.4 mm for the Fe3O4/graphene composites obtained by applying 100 cycles of Fe2O3 deposition followed by a hydrogen reduction. The enhanced absorption ability arises from the effective impedance matching, multiple interfacial polarization and increased magnetic loss from the added magnetic constituents. Moreover, compared with other recently reported materials, the composites have a lower filling ratio and smaller coating thickness resulting in significantly increased EM absorption properties. This demonstrates that nanoscale surface modification of magnetic particles on graphene by ALD is a very promising way to design lightweight and high-efficiency microwave absorbers.
基金Acknowledgements This work was supported by the Thousand Talents Plan, the National Natural Science Foundation of China (Nos. 21473169, 21673215, and 51402283), the Fundamental Research Funds for the Central Universities (Nos. WK2060030017 and WK2060190026), and the startup funds from the University of Science and Technology of China. This work was also supported by Hefei Science Center (No. 2015HSC-UP010).
文摘Selective hydrogenation is an important industrial catalytic process in chemical upgrading, where Pd-based catalysts are widely used because of their high hydrogenation activities. However, poor selectivity and short catalyst lifetime because of heavy coke formation have been major concerns. In this work, atomically dispersed Pd atoms were successfully synthesized on graphitic carbon nitride (g-C3N4) using atomic layer deposition. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) confirmed the dominant presence of isolated Pd atoms without Pd nanoparticle (NP) formation. During selective hydrogenation of acetylene in excess ethylene, the g-C3N4-supported Pd NP catalysts had strikingly higher ethylene selectivities than the conventional Pd/Al2O3 and Pd/SiO2 catalysts. In-situ X-ray photoemission spectroscopy revealed that the considerable charge transfer from the Pd NPs to g-C3N4 likely plays an important role in the catalytic performance enhancement. More impressively, the single-atom Pd1/C3N4 catalyst exhibited both higher ethylene selectivity and higher coking resistance. Our work demonstrates that the single-atom Pd catalyst is a promising candidate for improving both selectivity and coking-resistance in hydrogenation reactions.
基金This work was supported by the National Natural Science Foundation of China(51571134 and 51601108)the SDUST Research Fund(2014TDJH104).
文摘Micro-arc oxidation(MAO)coating with outstanding adhesion strength to Mg alloys has attracted more and more attention.However,owing to the porous structure,aggressive ions easily invaded the MAO/substrate interface through the through pores,limiting long-term corrosion resistance.Therefore,a dense and biocompatible tantalum oxide(Ta2O5)nanofilm was deposited on MAO coated Mg alloy AZ31 through atomic layer deposition(ALD)technique to seal the micropores and regulate the degradation rate.Surface micrography,chemical compositions and crystallographic structure were characterized using FE-SEM,EDS,XPS and XRD.The corrosion resistance of all samples was evaluated through electrochemical and hydrogen evolution tests.Results revealed that the Ta2O5 film mainly existed in the form of amorphousness.Moreover,uniform deposition of Ta2O5 film and effective sealing of micropores and microcracks in MAO coating were achieved.The current density(icorr)of the composite coating decreased three orders of magnitude than that of the substrate and MAO coating,improving corrosion resistance.Besides,the formation and corrosion resistance mechanisms of the composite coating were proposed.
基金financially supported by the National Natural Science Foundation of China(No.51772241)the Key Research Program of Shaanxi Province(No.2017ZDXM-GY-035)+2 种基金the Young Talent Support Plan of Xi’an Jiaotong University(No.DQ1J006)the Project from State Key Laboratory of Electrical Insulation and Power Equipment,Xi’an Jiaotong University(No.EIPE17306)the Fundamental Research Funds for the Central Universities(Nos.zrzd2017004,xjj2017076)for financial support
文摘Lithium (Li) metal has been considered as the most attractive anode materials for Li-ion batteries (LIBs) due to its high theoretic specific capacity. The formation of unstable solid electrolyte interphase (SEI) and dendritic Li on the metal anode, however, hindered its practical application. Herein, to address the issues, a Li-free electrode with ultrathin Al2O3 coated on reduced graphene oxide (rGO) membrane that covers a Cu foil current collector was developed. The composite electrode exhibits excellent interfacial protection of lithium metal deposited between Cu foil and rGO electrochemically. Firstly, it affords good Li^+ permeability from the electrolyte. Secondly, the ultrathin Al2O3 has sufficient mechanical strength to inhibit the penetration of Li dendrite. Li metal was observed uniformly deposited between rGO membrane and Cu collector, and stable cycle performance of Li plating/stripping with Coulombic efficiency of ~ 91.75% at the lOOth cycle is achieved in organic carbonate electrolyte without any additives.
基金supported by the Natural Science and Engineering Research Council of Canada (NSERC)the Canada Research Chair Program (CRC) and the University of Western Ontario (UWO)
文摘Noble single‐atom catalysts have rapidly been attracting attention due to their unique catalytic properties and maximized utilization.Atomic layer deposition(ALD)is an emerging powerful technique for large‐scale synthesis of stable single atom.In this review,we summarize recent developments of single atom synthesized by ALD as well as explore future research direction and trends.
基金financially supported by the National Natural Science Foundation of China(No.51972045,5197021414)the Fundamental Research Funds for the Chinese Central Universities,China(No.ZYGX2019J025)+4 种基金Sichuan Science and Technology Program(No.2020JDRC0015 and No.2020JDRC0045)Sichuan Science and Technology Innovation Talent Project(No.2021JDRC0021)the Vice-Chancellor fellowship scheme at RMIT Universitythe RMIT Micro Nano Research Facility(MNRF)in the Victorian node of the Australian National Fabrication Facility(ANFF)the RMIT Microscopy and Microanalysis Facility(RMMF)to support this work。
文摘Developing highly efficient magnetic microwave absorb-ers(MAs)is crucial,and yet challenging for anti-corrosion properties in extremely humid and salt-induced foggy environments.Herein,a dual-oxide shell of ZnO/Al_(2)O_(3) as a robust barrier to FeSiAl core is introduced to mitigate corrosion resistance.The FeSiAl@ZnO@Al_(2)O_(3) layer by layer hybrid structure is realized with atomic-scale precision through the atomic layer deposition technique.Owing to the unique hybrid structure,the FeSiAl@ZnO@Al_(2)O_(3) exhibits record-high micro-wave absorbing performance in low-frequency bands covering L and S bands with a minimum reflection loss(RLmin)of-50.6 dB at 3.4 GHz.Compared with pure FeSiAl(RLmin of-13.5 dB,a bandwidth of 0.5 GHz),the RLmin value and effective bandwidth of this designed novel absorber increased up to~3.7 and~3 times,respectively.Fur-thermore,the inert ceramic dual-shells have improved 9.0 times the anti-corrosion property of FeSiAl core by multistage barriers towards corrosive medium and obstruction of the electric circuit.This is attributed to the large charge transfer resistance,increased impedance modulus|Z|0.01 Hz,and frequency time constant of FeSiAl@ZnO@Al_(2)O_(3).The research demonstrates a promising platform toward the design of next-generation MAs with improved anti-corrosion properties.
基金supported by the National Natural Science Foundation of China(21872160,21802094,21673269)the National Science Fund for Distinguished Young Scholars(21825204)+1 种基金the National Key R&D Program of China(2017YFA0700101)the Natural Science Basic Research Plan in Shaanxi Province of China(2018JQ2038)~~
文摘Electrocatalysis is a promising approach to clean energy conversion due to its high efficiency and low environmental pollution. Noble metal materials have been studied to show high activity toward electrocatalyltic reactions, although such applications remain restricted by the high cost and poor durability of the noble metals. By precisely adjusting the catalyst composition, size, and structure, electrocatalysts with excellent performance can be obtained. Atomic layer deposition(ALD) is a technique used to produce ultrathin films and ultrafine nanoparticles at the atomic level. It possesses unique advantages for the controllable design and synthesis of electrocatalysts. Furthermore, the homogenous composition and structure of the electrocatalysts prepared by ALD favor the exploration of structure-reactivity relationships and catalytic mechanisms. In this review, the mechanism, characteristics, and advantages of ALD in fabricating nanostructures are introduced first. Subsequently, the problems associated with existing electrocatalysts and a series of recently developed ALD strategies to enhance the activity and durability of electrocatalysts are presented. For example, the deposition of ultrafine Pt nanoparticles to increase the utilization and activity of Pt, fabrication of core–shell, overcoat, nanotrap, and other novel structures to protect the noble-metal nanoparticles and enhance the catalyst stability. In addition, ALD developments in synthesizing non-noble metallic electrocatalysts are summarized and discussed. Finally, based on the current studies, an outlook for the ALD application in the design and synthesis of electrocatalysts is presented.
文摘Developing advanced technologies to stabilize positive electrodes of lithium ion batteries under high-voltage operation is becoming increasingly important,owing to the potential to achieve substantially enhanced energy density for applications such as portable electronics and electrical vehicles.Here,we deposited chemically inert and ionically conductive LiAlO2 interfacial layers on LiCoO2 electrodes using the atomic layer deposition technique.During prolonged cycling at high-voltage,the LiAlO2 coating not only prevented interfacial reactions between the LiCoO2 electrode and electrolyte,as confirmed by electrochemical impedance spectroscopy and Raman characterizations,but also allowed lithium ions to freely diffuse into LiCoO2 without sacrificing the power density.As a result,a capacity value close to 200 mA·h·g-1 was achieved for the LiCoO2 electrodes with commercial level loading densities,cycled at the cut-off potential of 4.6 V vs.Li+/Li for 50 stable cycles;this represents a 40% capacity gain,compared with the values obtained for commercial samples cycled at the cut-off potential of 4.2 V vs.Li+/Li.
文摘Impedance matching is important for achieving high-efficiency microwave absorbers. The high conductivity of dielectric loss materials such as pure metals and carbon nanomaterials generally results in poor absorption owing to the low impedance matching between the absorbers and air. Carbon nanostructures are very promising candidates for high-efficiency absorption because of their attractive features including low density, high surface area, and good stability. Herein, a new strategy is proposed to improve the impedance matching of dielectric loss materials using electrospun carbon nanofibers as an example. The carbon nanofibers are coated with specifically designed gradient multilayer nanofilms with gradually increasing electroconductibility synthesized by doping ZnO with different A1203 content (AZO) by atomic layer deposition. The gradient nanofilms are composed of five layers of dielectric films, namely, pure A1203, AZO (5:1, the pulse cycle ratio of ZnO to A1203), pure ZnO, AZO (10:1), and AZO (20:1). The versatile gradient films serve as intermediate layers to tune the impedance matching between air and the carbon nanofiber surfaces. Therefore, the carbon nanofibers coated with gradient films of rationally selected thicknesses exhibit remarkably enhanced microwave absorption performance, and the optimal reflection loss reaches -58.5 dB at 16.2 GHz with a thickness of only 1.8 mm. This work can help further understand the contribution of impedance matching to microwave absorption. Our strategy is general and can be applied to improve the absorption properties of other dielectric loss materials and even for applications in other fields.