A simple preparation of ultrathin nanoporous gold film was described. Copper and gold were used to fabricate Cu-Au alloy films through vacuum deposition. The formation of nanoporous gold films from the alloy films inv...A simple preparation of ultrathin nanoporous gold film was described. Copper and gold were used to fabricate Cu-Au alloy films through vacuum deposition. The formation of nanoporous gold films from the alloy films involved thermal process and chemical etch by hydrochloric acid or by nitric acid. The free-standing nanoporous gold films have been analyzed by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray photoelectron spectrometer （XPS） and surface-enhanced Raman scattering （SELLS）. R was noted that the nanoporous gold film etched by hydrochloric acid is uniform with a cover of fog-like moieties.展开更多
Grain boundaries(GBs),as a prevalent structural characteristic,play a crucial role in the deformation of nanoporous metals with nanosized grains and ligaments.However,the fundamental understanding of GB-mediated defor...Grain boundaries(GBs),as a prevalent structural characteristic,play a crucial role in the deformation of nanoporous metals with nanosized grains and ligaments.However,the fundamental understanding of GB-mediated deformation is still lacking because the plastic behavior of discrete ligaments involving GBs remains to be unknown.Here,we report atomic scale visualizations of coupled GB dislocation climb and glide in nanoporous gold ligaments with low-angle GBs via in situ tensile straining inside a Cs-corrected transmission electron microscope.The zig-zag motion paths of GB dislocations are precisely determined by real-time tracking of the movements of dislocation cores.The concurrent climb and glide of the dislocation arrays are confined to a narrow GB region,greatly enhancing GB diffusion in the bicrystal ligament.Our findings of coupled dislocation climb and glide shine a light on the room-temperature deformation of nanoporous metals and provide a time-dependent atomic-level physical image for GB engineering.展开更多
Solid-state nanopores with controllable pore size and morphology have huge application potential.However,it has been very challenging to process sub-10 nm silicon nanopore arrays with high efficiency and high quality ...Solid-state nanopores with controllable pore size and morphology have huge application potential.However,it has been very challenging to process sub-10 nm silicon nanopore arrays with high efficiency and high quality at low cost.In this study,a method combining metal-assisted chemical etching and machine learning is proposed to fabricate sub-10 nm nanopore arrays on silicon wafers with various dopant types and concentrations.Through a SVM algorithm,the relationship between the nanopore structures and the fabrication conditions,including the etching solution,etching time,dopant type,and concentration,was modeled and experimentally verified.Based on this,a processing parameter window for generating regular nanopore arrays on silicon wafers with variable doping types and concentrations was obtained.The proposed machine-learning-assisted etching method will provide a feasible and economical way to process high-quality silicon nanopores,nanostructures,and devices.展开更多
The oxygen reduction reaction （ORR） and oxygen evolution reaction （OER） are crucial processes for energy conversion/storage systems, such as fuel cells, metal-air batteries, and water splitting. However, both reac...The oxygen reduction reaction （ORR） and oxygen evolution reaction （OER） are crucial processes for energy conversion/storage systems, such as fuel cells, metal-air batteries, and water splitting. However, both reactions are severely restricted by their sluggish kinetics, thus requiring highly active, cost-effective, and durable electrocatalysts. Herein, we develop novel bifunctional nanocatalysts through surface nanoengineering of dealloying-driven nanoporous gold （NPG）. Pd overlayers were precisely deposited onto the NPG ligament surface by epitaxial layer-by-layer growth. More importantly, the obtained NPG-Pd overlayer nanocatalysts exhibit remarkably enhanced electrocatalytic activities toward both the ORR and OER in alkaline media, benchmarked against a state- of-the-art Pt/C catalyst. The improved electrocatalytic performance is rationalized by the unique three-dimensional nanoarchitecture of NPG, enhanced Pd utilization efficiency from precise control of the Pd overlayers, and change in electronic structure, as revealed by density functional theory calculations.展开更多
A simple and rapid approach for the electrochemical synthesis of Ag nanoparticles-coated gold nanoporous film (AgGNF) on a gold substrate was reported. The solid gold electrode (SGE) was directly anodized under a high...A simple and rapid approach for the electrochemical synthesis of Ag nanoparticles-coated gold nanoporous film (AgGNF) on a gold substrate was reported. The solid gold electrode (SGE) was directly anodized under a high potential of 5 V, and then reduced to obtain gold nanoporous film (AuNF) by freshly prepared ascorbic acid. The Ag nanoparticles (AgNPs) were grown on the AuNF electrode by potential-step electrodeposition. The resulting AgGNF composites electrodes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy and cyclic voltammetry (CV). As-prepared AgGNF electrode was used as a kind of superior sensor for Cr(VI) detection, which exhibited better electrocatalytic behavior than those of AuNF and SGE under identical conditions. Such a designed AgGNF nanocomposites electrode showed outstanding sensitivity (about 0.15 nA/ppb) and favorable reproducibility for Cr(VI) detection. The dependence of reduction current on Cr(VI) concentration is linear from 2 to 370 ppb with a low detection limit of 0.65 ppb. Interferences from other heavy metals ions (Cr3+, Cu2+, Pb2+, As3+ and Hg2+) associated with Cr(VI) analysis could be effectively diminished. The present method proves to be rapid, reliable, sensitive and low-cost.展开更多
Design and fabrication of highly efficient and stable electrocatalysts remain key challenges in green energy technologies such as low-temperature direct liquid fuel cells.Based on in-depth theoretical calculations,her...Design and fabrication of highly efficient and stable electrocatalysts remain key challenges in green energy technologies such as low-temperature direct liquid fuel cells.Based on in-depth theoretical calculations,here we demonstrate that surface Pd atoms with high coordination numbers(HCNs)can effectively modulate their adsorption energies for CO and OH,and thus achieve very high performance for formic acid electro-oxidation reaction(FAOR).Based on epitaxial coating Pd atomic layers onto nanoporous gold(NPG)thin membranes and a slight further decoration of Au clusters on top,the resulted core-shell structured NPG-Pd-Au electrocatalyst can demonstrate Pd intrinsic and mass activities of 8.62 mA·cm^(-2)and 27.25 A·mg^(-1)respectively at the peak potential around 0.33 V versus saturated calomel electrode toward FAOR,which are far better than those of commercial Pd/C catalysts(1.09 mA·cm^(-2)and 0.32 A·mg^(-1))tested under the same conditions.Moreover,the membrane electrode assemblies based on these low precious metal loading electrodes can achieve an anode Pd power efficiency over 10 W·mg^(-1)in a direct formic acid fuel cell,which is two orders of magnitude higher than that of the commercial Pd/C.These results provide new inspirations for the development of revolutionary electrodes for energy technologies in a rational manner.展开更多
The combination of focused ion beam (FIB) with scanning electron microscopy (SEM), also known as FIB-SEM tomography, has become a powerful 3D imaging technique at the nanometer scale. This method uses an ion beam to m...The combination of focused ion beam (FIB) with scanning electron microscopy (SEM), also known as FIB-SEM tomography, has become a powerful 3D imaging technique at the nanometer scale. This method uses an ion beam to mill away a thin slice of material, which is then block-face imaged using an electron beam. With consecutive slicing along the z-axis and subsequent imaging, a volume of interest can be reconstructed from the images and further analyzed. Hierarchical nanoporous gold (HNPG) exhibits unique structural properties and has a ligament size of 15–110 nm and pore size of 5–20 nm. Accurate reconstruction of its image is crucial in determining its mechanical and other properties. Slice thickness is one of the most critical and uncertain parameters in FIB-SEM tomography. For HNPG, the slice thickness should be at least half as thin as the pore size and, in our approach, should not exceed 10 nm. Variations in slice thickness are caused by various microscope and sample parameters, e.g., converged ion milling beam shape, charging effects, beam drift, or sample surface roughness. Determining and optimizing the actual slice thickness variation appear challenging. In this work, we examine the influence of ion beam scan resolution and the dwell time on the mean and standard deviation of slice thickness. After optimizing the resolution and dwell time to achieve the target slice thickness and lowest possible standard deviation, we apply these parameters to analyze an actual HNPG sample. Our approach can determine the thickness of each slice along the z-axis and estimate the deviation of the milling process along the y-axis (slow imaging axis). For this function, we create a multi-ruler structure integrated with the HNPG sample.展开更多
The increasing demand for portable electronic devices and hybrid electric vehicles stimulates the develop- ment of supercapacitors as an advanced energy storage system. Here, we demonstrate a binder-free nickel hydrox...The increasing demand for portable electronic devices and hybrid electric vehicles stimulates the develop- ment of supercapacitors as an advanced energy storage system. Here, we demonstrate a binder-free nickel hydroxide@nano- porous gold/Ni foam （Ni（OH）2@NPG/Ni foam） electrode for high-performance supercapacitors, which is prepared by a facile three-step fabrication route including electrodeposition of Au-Sn alloy on Ni foam, chemical dealloying of Sn and electrodepostion of Ni（OH）2 on NPG/Ni foam. Such Ni（OH）2@NPG/Ni foam electrode is composed of a thin layer of conformable Ni（OH）2 nanoflakes supported on three-di- mensional （3D） hierarchically porous NPG/Ni foam substrate. The resulting Ni（OH）2@NPG/Ni foam electrode can offer highways for both electron transfer and ion transport and lead to an excellent electrochemical performance with an ultrahigh specific capacitance of 3,380 F g-1 at a current density of 2 A g-1. Even when the current density was increased to 50 A g-1, it still retained a high capacitance of 1,927 F g-1. The promising performance of the Ni（OH）2@NPG/Ni foam elec- trode is mainly ascribed to the 3D hierarchical porosity and the highly conductive network on the NPG/Ni foam composite current collector, as well as the conformal electrodeposition of Ni（OH）2 active material on the NPG/Ni foam, which induces the formation of interconnected porosity both on the top surface and on the inner surface of the electrode. This in- spiring electrochemical performance would make the as-de- signed electrode material become one of the most promising candidates for future electrochemical energy storage systems.展开更多
纳米多孔金(NPG)具有高曲率、高比表面积的结构特征,且比强度较高,作为一种结构功能一体化材料受到广泛关注。然而,影响NPG实际应用的最大障碍之一是其在拉伸作用下内部单根韧带失效导致的塑性失稳。过去的研究主要集中在宏观力学实验...纳米多孔金(NPG)具有高曲率、高比表面积的结构特征,且比强度较高,作为一种结构功能一体化材料受到广泛关注。然而,影响NPG实际应用的最大障碍之一是其在拉伸作用下内部单根韧带失效导致的塑性失稳。过去的研究主要集中在宏观力学实验的研究,无法直接观察单根韧带的塑性变形行为。随着原位透射电子显微镜(transmission electron microscopy,TEM)的发展,已具备从原子尺度研究NPG中单根韧带塑性变形过程的能力,这对理解NPG变形机理进而合理设计制备高塑性纳米多孔结构金属具有重要意义。本文主要以近几年利用球差校正透射电子显微镜(Cs⁃corrected TEM)原位原子尺度研究NPG塑性变形的系列工作为例,简要综述了NPG单根韧带在塑性变形过程中位错运动(攀移和滑移)和表面原子扩散行为的最新进展,并对纳米结构金属材料的未来研究进行了展望。展开更多
Three-dimensional(3D)nanoporous gold(NPG)shows promising applications in various fields.However,its most common fabrication strategy(i.e.,dealloying)faces the problems of high energy consumption,resource waste,the use...Three-dimensional(3D)nanoporous gold(NPG)shows promising applications in various fields.However,its most common fabrication strategy(i.e.,dealloying)faces the problems of high energy consumption,resource waste,the use of corrosive solvent,and residue of the sacrificial component.Here,we report a general bottom-up nanowelding strategy to fabricate high-purity NPG from Au nanoparticles(NPs),accomplished via interfacial self-assembly of the Au NPs into monolayer Au NP film,its subsequent layer-by-layer transfer onto a solid substrate,and direct current(DC)nanowelding.We show that the DC nanowelding process can gradually evolve the layered Au NP film into NPG at low temperatures within 10 s,while not damaging their spherical structure.This is because during the nanowelding,electrons are preferred to be localized at the high-resistance NP/NP junctions,whose electrostatic repulsion in turn strengthens their surface atom diffusion to initiate a mild solid-state diffusion nanowelding.Furthermore,when using differently sized Au NPs as the starting building blocks,this strategy allows readily tuning the thickness,ligament size,and pore size,thereby offering great flexibility to create functional porous nanomaterials,e.g.,electrocatalyst for methanol electrooxidation.Surely,low-temperature nanowelding can play a role for the production of diverse nanoporous materials from other NPs beyond Au NPs.展开更多
Nanoporous gold （np-Au） is an emerging nanostructured material that exhibits many desirable properties, including high electrical and thermal conductivity, high surface area-to-volume ratio, tunable pore morphology ...Nanoporous gold （np-Au） is an emerging nanostructured material that exhibits many desirable properties, including high electrical and thermal conductivity, high surface area-to-volume ratio, tunable pore morphology well-established surface-binding chemistry, and compatibility with microfabrication. These features make np-Au a popular material for use in fuel cells, optical and electrical biosensors, drug delivery vehicles, neural electrode coatings, and as a model system for nanoscale mechanics. In each of its many applications, np-Au morphology plays an essential role in the overall device operation. Therefore, precise morphological control is necessary to attain optimal device performance. Traditionally thermal treatment by furnaces and hot plates is used to obtain np-Au with self-similar but coarser morphologies. However, this approach lacks the ability to create different morphologies on a single substrate and requires high temperatures （〉 250 ℃） incompatible with most plastic substrates. Herein, we report electro-annealing as a novel method that permits control of the extent and location of pore coarsening on a single substrate in one fast treatment step. The electro-annealing entails much lower temperatures （〈 150 ℃） than traditional thermal treatment, putatively due to electrically assisted phenomena contributing to the thermally activated surface diffusion of gold atoms, responsible for coarsening. Overall, this approach is easily scaled to display multiple pore morphologies on a single chip, therefore enabling high-throughput screening of optimal nanostructures for specific applications.展开更多
A series of large-scale molecular dynamics(MD) simulations has been performed to study the effects of grain size and ligament diameter on the mechanical properties of nanocrystalline nanoporous gold. Such simulations ...A series of large-scale molecular dynamics(MD) simulations has been performed to study the effects of grain size and ligament diameter on the mechanical properties of nanocrystalline nanoporous gold. Such simulations indicate that the principal deformation mechanism is a combination of grain boundary sliding, grain rotation and dislocation movement. The results of uniaxial tensile tests reveal the presence of a reverse Hall-Petch relation between strength and nominal grain size, rather than the conventional Hall-Petch relationship in the present range of nominal grain size(7.9–52.7 nm). An increase of flow stress may possibly attribute to the lower total proportion of grain boundary sliding and grain rotation in the deformation of samples with larger grain size. The Young's modulus shows a linear relation with the reciprocal of nominal grain size, which depends largely on the volume fraction of grain boundaries and thus decreasing grain size leads to relatively lower Young's modulus. MD simulations on samples with ligament diameter ranging from 4.07 to 8.10 nm are also carried out and results show that the increasing ligament diameter resulted in decreased flow stress and increased Young's modulus.展开更多
基金This work was supported by the National Natural Science Foundation of China(No.60171008)Shanghai Science and Technology Committee(No.0214nm005,No.0452nm087).
文摘A simple preparation of ultrathin nanoporous gold film was described. Copper and gold were used to fabricate Cu-Au alloy films through vacuum deposition. The formation of nanoporous gold films from the alloy films involved thermal process and chemical etch by hydrochloric acid or by nitric acid. The free-standing nanoporous gold films have been analyzed by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray photoelectron spectrometer （XPS） and surface-enhanced Raman scattering （SELLS）. R was noted that the nanoporous gold film etched by hydrochloric acid is uniform with a cover of fog-like moieties.
基金supported by the National Natural Science Foundation of China(Nos.52173224,52130105,and 51821001)Natural Science Foundation of Shanghai(No.21ZR1431200)the Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learning.
文摘Grain boundaries(GBs),as a prevalent structural characteristic,play a crucial role in the deformation of nanoporous metals with nanosized grains and ligaments.However,the fundamental understanding of GB-mediated deformation is still lacking because the plastic behavior of discrete ligaments involving GBs remains to be unknown.Here,we report atomic scale visualizations of coupled GB dislocation climb and glide in nanoporous gold ligaments with low-angle GBs via in situ tensile straining inside a Cs-corrected transmission electron microscope.The zig-zag motion paths of GB dislocations are precisely determined by real-time tracking of the movements of dislocation cores.The concurrent climb and glide of the dislocation arrays are confined to a narrow GB region,greatly enhancing GB diffusion in the bicrystal ligament.Our findings of coupled dislocation climb and glide shine a light on the room-temperature deformation of nanoporous metals and provide a time-dependent atomic-level physical image for GB engineering.
基金supported by the National Natural Science Foundation of China[Grant Nos.51975127,U20A6004]the Guangdong-Hong Kong Technology Coopeartion[Grant No.GHP/112/19GD]from Hong Kong Innovation and Technology Commission+1 种基金Research and Development Program of Guangdong Province[Grant No.2020A0505140008]the Fund of Key-Area Research and Development Program of Guangdong Province[Grant No.2018B090906002]。
文摘Solid-state nanopores with controllable pore size and morphology have huge application potential.However,it has been very challenging to process sub-10 nm silicon nanopore arrays with high efficiency and high quality at low cost.In this study,a method combining metal-assisted chemical etching and machine learning is proposed to fabricate sub-10 nm nanopore arrays on silicon wafers with various dopant types and concentrations.Through a SVM algorithm,the relationship between the nanopore structures and the fabrication conditions,including the etching solution,etching time,dopant type,and concentration,was modeled and experimentally verified.Based on this,a processing parameter window for generating regular nanopore arrays on silicon wafers with variable doping types and concentrations was obtained.The proposed machine-learning-assisted etching method will provide a feasible and economical way to process high-quality silicon nanopores,nanostructures,and devices.
基金The authors gratefully acknowledge financial support by the National Basic Research Program of China （No. 2012CB932800）, National Natural Science Foundation of China （Nos. 51371106 and 51222202）, and Young Tip-top Talent Support Project （the Organization Department of the Central Committee of the CPC）. The Institute of Materials of Ruhr University Bochum （Germany） is acknowledged for the support of SEM and TEM characterization. This work also made use of the resources of the Center of Electron Microscopy of Zhejiang University.
文摘The oxygen reduction reaction （ORR） and oxygen evolution reaction （OER） are crucial processes for energy conversion/storage systems, such as fuel cells, metal-air batteries, and water splitting. However, both reactions are severely restricted by their sluggish kinetics, thus requiring highly active, cost-effective, and durable electrocatalysts. Herein, we develop novel bifunctional nanocatalysts through surface nanoengineering of dealloying-driven nanoporous gold （NPG）. Pd overlayers were precisely deposited onto the NPG ligament surface by epitaxial layer-by-layer growth. More importantly, the obtained NPG-Pd overlayer nanocatalysts exhibit remarkably enhanced electrocatalytic activities toward both the ORR and OER in alkaline media, benchmarked against a state- of-the-art Pt/C catalyst. The improved electrocatalytic performance is rationalized by the unique three-dimensional nanoarchitecture of NPG, enhanced Pd utilization efficiency from precise control of the Pd overlayers, and change in electronic structure, as revealed by density functional theory calculations.
基金supported by the National Natural Science Foundation of China (21005014)the Foundation of Donghua University (113-10-0044029)
文摘A simple and rapid approach for the electrochemical synthesis of Ag nanoparticles-coated gold nanoporous film (AgGNF) on a gold substrate was reported. The solid gold electrode (SGE) was directly anodized under a high potential of 5 V, and then reduced to obtain gold nanoporous film (AuNF) by freshly prepared ascorbic acid. The Ag nanoparticles (AgNPs) were grown on the AuNF electrode by potential-step electrodeposition. The resulting AgGNF composites electrodes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy and cyclic voltammetry (CV). As-prepared AgGNF electrode was used as a kind of superior sensor for Cr(VI) detection, which exhibited better electrocatalytic behavior than those of AuNF and SGE under identical conditions. Such a designed AgGNF nanocomposites electrode showed outstanding sensitivity (about 0.15 nA/ppb) and favorable reproducibility for Cr(VI) detection. The dependence of reduction current on Cr(VI) concentration is linear from 2 to 370 ppb with a low detection limit of 0.65 ppb. Interferences from other heavy metals ions (Cr3+, Cu2+, Pb2+, As3+ and Hg2+) associated with Cr(VI) analysis could be effectively diminished. The present method proves to be rapid, reliable, sensitive and low-cost.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.51901156,52073214,and U1804255)the National Science Fund for Distinguished Young Scholars(No.51825102).
文摘Design and fabrication of highly efficient and stable electrocatalysts remain key challenges in green energy technologies such as low-temperature direct liquid fuel cells.Based on in-depth theoretical calculations,here we demonstrate that surface Pd atoms with high coordination numbers(HCNs)can effectively modulate their adsorption energies for CO and OH,and thus achieve very high performance for formic acid electro-oxidation reaction(FAOR).Based on epitaxial coating Pd atomic layers onto nanoporous gold(NPG)thin membranes and a slight further decoration of Au clusters on top,the resulted core-shell structured NPG-Pd-Au electrocatalyst can demonstrate Pd intrinsic and mass activities of 8.62 mA·cm^(-2)and 27.25 A·mg^(-1)respectively at the peak potential around 0.33 V versus saturated calomel electrode toward FAOR,which are far better than those of commercial Pd/C catalysts(1.09 mA·cm^(-2)and 0.32 A·mg^(-1))tested under the same conditions.Moreover,the membrane electrode assemblies based on these low precious metal loading electrodes can achieve an anode Pd power efficiency over 10 W·mg^(-1)in a direct formic acid fuel cell,which is two orders of magnitude higher than that of the commercial Pd/C.These results provide new inspirations for the development of revolutionary electrodes for energy technologies in a rational manner.
基金funded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)—Project SFB 986—Tailor-Made Multiscale Materials Systems,subproject B9—Microstructure-based classification and mechanical analysis of nanoporous metals by machine learningOpen Access funding enabled and organized by Projekt DEAL.
文摘The combination of focused ion beam (FIB) with scanning electron microscopy (SEM), also known as FIB-SEM tomography, has become a powerful 3D imaging technique at the nanometer scale. This method uses an ion beam to mill away a thin slice of material, which is then block-face imaged using an electron beam. With consecutive slicing along the z-axis and subsequent imaging, a volume of interest can be reconstructed from the images and further analyzed. Hierarchical nanoporous gold (HNPG) exhibits unique structural properties and has a ligament size of 15–110 nm and pore size of 5–20 nm. Accurate reconstruction of its image is crucial in determining its mechanical and other properties. Slice thickness is one of the most critical and uncertain parameters in FIB-SEM tomography. For HNPG, the slice thickness should be at least half as thin as the pore size and, in our approach, should not exceed 10 nm. Variations in slice thickness are caused by various microscope and sample parameters, e.g., converged ion milling beam shape, charging effects, beam drift, or sample surface roughness. Determining and optimizing the actual slice thickness variation appear challenging. In this work, we examine the influence of ion beam scan resolution and the dwell time on the mean and standard deviation of slice thickness. After optimizing the resolution and dwell time to achieve the target slice thickness and lowest possible standard deviation, we apply these parameters to analyze an actual HNPG sample. Our approach can determine the thickness of each slice along the z-axis and estimate the deviation of the milling process along the y-axis (slow imaging axis). For this function, we create a multi-ruler structure integrated with the HNPG sample.
基金financially supported by the National Natural Science Foundation of China (21673051,51604086)the Guangdong Science and Technology Department (2016A010104015)+4 种基金the Pearl River Scholar Funded Scheme of Guangdong Province Universities and Colleges (2015)the Science and Technology Program of Guangzhou (201604030037)the 'One-hundred Talents plan' (220418056)the 'One-hundred Young Talents plan' (220413126)the Youth Foundation (252151038) of Guangdong University of Technology
文摘The increasing demand for portable electronic devices and hybrid electric vehicles stimulates the develop- ment of supercapacitors as an advanced energy storage system. Here, we demonstrate a binder-free nickel hydroxide@nano- porous gold/Ni foam （Ni（OH）2@NPG/Ni foam） electrode for high-performance supercapacitors, which is prepared by a facile three-step fabrication route including electrodeposition of Au-Sn alloy on Ni foam, chemical dealloying of Sn and electrodepostion of Ni（OH）2 on NPG/Ni foam. Such Ni（OH）2@NPG/Ni foam electrode is composed of a thin layer of conformable Ni（OH）2 nanoflakes supported on three-di- mensional （3D） hierarchically porous NPG/Ni foam substrate. The resulting Ni（OH）2@NPG/Ni foam electrode can offer highways for both electron transfer and ion transport and lead to an excellent electrochemical performance with an ultrahigh specific capacitance of 3,380 F g-1 at a current density of 2 A g-1. Even when the current density was increased to 50 A g-1, it still retained a high capacitance of 1,927 F g-1. The promising performance of the Ni（OH）2@NPG/Ni foam elec- trode is mainly ascribed to the 3D hierarchical porosity and the highly conductive network on the NPG/Ni foam composite current collector, as well as the conformal electrodeposition of Ni（OH）2 active material on the NPG/Ni foam, which induces the formation of interconnected porosity both on the top surface and on the inner surface of the electrode. This in- spiring electrochemical performance would make the as-de- signed electrode material become one of the most promising candidates for future electrochemical energy storage systems.
文摘纳米多孔金(NPG)具有高曲率、高比表面积的结构特征,且比强度较高,作为一种结构功能一体化材料受到广泛关注。然而,影响NPG实际应用的最大障碍之一是其在拉伸作用下内部单根韧带失效导致的塑性失稳。过去的研究主要集中在宏观力学实验的研究,无法直接观察单根韧带的塑性变形行为。随着原位透射电子显微镜(transmission electron microscopy,TEM)的发展,已具备从原子尺度研究NPG中单根韧带塑性变形过程的能力,这对理解NPG变形机理进而合理设计制备高塑性纳米多孔结构金属具有重要意义。本文主要以近几年利用球差校正透射电子显微镜(Cs⁃corrected TEM)原位原子尺度研究NPG塑性变形的系列工作为例,简要综述了NPG单根韧带在塑性变形过程中位错运动(攀移和滑移)和表面原子扩散行为的最新进展,并对纳米结构金属材料的未来研究进行了展望。
基金supported by the National Natural Science Foundation of China (21872047 and 21673070)Hunan Key Laboratory of Two-Dimensional Materials (2018TP1010)。
文摘Three-dimensional(3D)nanoporous gold(NPG)shows promising applications in various fields.However,its most common fabrication strategy(i.e.,dealloying)faces the problems of high energy consumption,resource waste,the use of corrosive solvent,and residue of the sacrificial component.Here,we report a general bottom-up nanowelding strategy to fabricate high-purity NPG from Au nanoparticles(NPs),accomplished via interfacial self-assembly of the Au NPs into monolayer Au NP film,its subsequent layer-by-layer transfer onto a solid substrate,and direct current(DC)nanowelding.We show that the DC nanowelding process can gradually evolve the layered Au NP film into NPG at low temperatures within 10 s,while not damaging their spherical structure.This is because during the nanowelding,electrons are preferred to be localized at the high-resistance NP/NP junctions,whose electrostatic repulsion in turn strengthens their surface atom diffusion to initiate a mild solid-state diffusion nanowelding.Furthermore,when using differently sized Au NPs as the starting building blocks,this strategy allows readily tuning the thickness,ligament size,and pore size,thereby offering great flexibility to create functional porous nanomaterials,e.g.,electrocatalyst for methanol electrooxidation.Surely,low-temperature nanowelding can play a role for the production of diverse nanoporous materials from other NPs beyond Au NPs.
文摘Nanoporous gold （np-Au） is an emerging nanostructured material that exhibits many desirable properties, including high electrical and thermal conductivity, high surface area-to-volume ratio, tunable pore morphology well-established surface-binding chemistry, and compatibility with microfabrication. These features make np-Au a popular material for use in fuel cells, optical and electrical biosensors, drug delivery vehicles, neural electrode coatings, and as a model system for nanoscale mechanics. In each of its many applications, np-Au morphology plays an essential role in the overall device operation. Therefore, precise morphological control is necessary to attain optimal device performance. Traditionally thermal treatment by furnaces and hot plates is used to obtain np-Au with self-similar but coarser morphologies. However, this approach lacks the ability to create different morphologies on a single substrate and requires high temperatures （〉 250 ℃） incompatible with most plastic substrates. Herein, we report electro-annealing as a novel method that permits control of the extent and location of pore coarsening on a single substrate in one fast treatment step. The electro-annealing entails much lower temperatures （〈 150 ℃） than traditional thermal treatment, putatively due to electrically assisted phenomena contributing to the thermally activated surface diffusion of gold atoms, responsible for coarsening. Overall, this approach is easily scaled to display multiple pore morphologies on a single chip, therefore enabling high-throughput screening of optimal nanostructures for specific applications.
基金supported by the National Natural Science Foundation of China(Grant Nos.11102140&51575404)
文摘A series of large-scale molecular dynamics(MD) simulations has been performed to study the effects of grain size and ligament diameter on the mechanical properties of nanocrystalline nanoporous gold. Such simulations indicate that the principal deformation mechanism is a combination of grain boundary sliding, grain rotation and dislocation movement. The results of uniaxial tensile tests reveal the presence of a reverse Hall-Petch relation between strength and nominal grain size, rather than the conventional Hall-Petch relationship in the present range of nominal grain size(7.9–52.7 nm). An increase of flow stress may possibly attribute to the lower total proportion of grain boundary sliding and grain rotation in the deformation of samples with larger grain size. The Young's modulus shows a linear relation with the reciprocal of nominal grain size, which depends largely on the volume fraction of grain boundaries and thus decreasing grain size leads to relatively lower Young's modulus. MD simulations on samples with ligament diameter ranging from 4.07 to 8.10 nm are also carried out and results show that the increasing ligament diameter resulted in decreased flow stress and increased Young's modulus.
