| Nanoporous metals(NPMs)are such a kind of new functional nanometer materials with three-dimensional,bicontinuous,quasi-periodic ligament-channel structure.The well combination of preeminent electric/thermal conductivity of metals with high specific surface area of nano materials makes them exhibit great application potentials in catalysis,sensors,energy storage/conversion and biomedical science.Dealloying,as one of the main methods to fabricate NMPs,has been successfully applied to fabricate NPMs with different sizes and dimensions and becomes one of the hottest research topics in the advanced material and nanotechnology field.However,the selective dissolution of elements usually accompanies with the volume shrinkage and stress corrosion cracking of precursor alloys,resulting in the absence of tensile plasticity of the as-fabricated NPMs.Consequently,the intrinsic brittleness of NPMs has become the main factor that impedes their practical applications.Furthermore,the NPMs obtained via dealloying are usually composed of nanopores and ligaments with single size distribution,which could effectively improve the specific surface area and active catalytic sites but are not favorable for the rapid mass transfer and signal response.Based on above research background,in this dissertation,from the design of precursor alloys,utilizing the liquid Ga/vapor Zn-assisted alloying strategy and combining with various dealloying methods,the substrate-supported NPMs and hierarchically nested-network NPMs with three different length scales are successfully prepared.Moreover,the evolution of component,structure,morphology,as well as related properties and applications have been further investigated.Firstly,based on the fluidity of liquid Ga,utilizing the painting-alloying-dealloying strategy,the flexible substrate-supported nanoporous Cu film(3D porous Cu)was successfully fabricated.The 3D porous Cu exhibits a typical three-dimensional bicontinuous ligamentchannel structure,which possesses high specific surface area,excellent flexibility and mechanical tensile plasticity.Noticeably,the painting-alloying-dealloying strategy shows the advantages of easy operation,low cost,high efficiency and is suitable for scale production.When directly used as the current collector in Li metal batteries,3D porous Cu exhibits a coulombic efficiency of 98.2%over 200 cycles at 0.5 mA·cm-2 in half cells,and a long cycling life surpassing 700 h at 0.5 mA·cm-2 in symmetric cells,much superior to commercial Cu film.Besides,the full cells with a LiFePO4 cathode show good cycling stability and excellent rate capability,further demonstrating the potential application value of 3D porous Cu current collector.The deposition morphologies of Li metal on the two kinds of current collectors are observed utilizing the scanning electron microscopy(SEM).The results show that the Li metal deposited on the surface of 3D porous Cu current collector is more homogeneous and compact，which illustrates that the nanoporous structure can alleviate the growth of Li dendrites.Secondly,utilizing the same painting-alloying-dealloying strategy,taking the Ag-Ga system as the example,the substrate-supported nanoporous Ag film was fabricated to further explore the influence of liquid Ga-assisted alloying strategy on the macro/micro structure modulation and mechanical tensile properties.The study shows that during the alloying process.the bulk-like Ag3Ga mainly forms in the Ag-rich zone while the wire-like Ag3Ga prevails in the Ga-rich zone,and the thickness of alloy layer versus mass loading of Ga follows a good linear relationship.After dealloying,the bimodal wire-like and unimodal bulk-like nanoporous Ag is obtained because of the "inheritance effect".Moreover,the thickness of nanoporous layer matches well with the alloy layer,demonstrating the controllability of nanoporous layer.The in-situ X-ray diffraction(XRD)results reveal that during the dealloying process of Ag3Ga,no other intermediate phases appear and the dealloying process can be described by the dissolution-surface diffusion model.The nanoindentation and tensile tests show that owing to the good adhesion and modulus matching,the nanoporous layer could deform synergistically with the substrate when subjected to the external force,which could greatly improve the mechanical tensile properties of nanoporous Ag films.Thirdly,based on the vapor pressure difference between Zn and other metals,taking Ag as the example and utilizing the vapor phase alloying(VPA)-dealloying strategy,the substratesupported nanoporous Ag was successfully fabricated.By modulating the VPA time and temperature,the thickness and phase composition(AgZn-Ag5Zn8-AgZn3)of alloy layer could be controlled,which could realize the coupling regulation of macro thickness and micro morphology toward nanoporous layers after dealloying.The in-situ XRD and SEM results reveal that the dissolution of Zn proceeds almost layer by layer and no other intermediate phases appear during the dealloying process of AgZn3.Besides,the nanoindentation and tensile tests show that the substrate-supported nanoporous Ag exhibits obvious plastic deformation stage under the support and restrict effect of Ag substrate.The excellent mechanical tensile properties could be attributed to the good interfacial adhesion and modulus matching between the nanoporous layer and substrate.Additionally,the metals with different macro sizes and shapes,such as Ag.Au.Cu.Co.Ni.can be fabricated into nanoporous structure with good selfsupporting properties by the VPA-dealloying strategy;meanwhile,the nanoporous Ni foam fabricated by this strategy exhibits better catalytic performance than commercial Ni foam when applied as the electrode in hydrogen evolution reaction,demonstrating the generalizability and application value of VPA-dealloying strategy.Finally,based on above study,the ternary dilute precursor alloy Ag-Au-Zn with a low content of Au was designed and prepared.Utilizing the length scale difference of ligaments fabricated by different dealloying methods,combining vapor phase dealloying,annealing and electrochemical dealloying,the nanoporous Au with three-level structural hierarchy(N3PG)was successfully fabricated.SEM and transmission electron microscopy(TEM)results show that the hierarchy level evolution mainly involves four stages:micron scale(MP-Ag95Au5),micron scale-nanoscale(NP-Ag68Au32),micron scale-submicron scale(SP-Ag68Au32),micron scale-submicron scale-nanoscale(N3PG).The average ligament sizes of N3PG on different hierarchy levels are 5866.8±1445.5,509.9±106.0 and 20.1±3.0 nm,respectively.The step potential measurements and cyclic voltammetry scans reveal the interpenetrating pores with micron-and submicron-scale in N3PG jointly provide multi-level channels for charge transfer,improving the charge transfer rate and numbers.On the other hand,nanoscale pores of N3PG guarantee its electrochemical active surface area.The solar water evaporation test shows that N3PG exhibits excellent water evaporation performance,demonstrating its potential application value.In summary,based on the flexibility and reactivity of liquid/vapor metal,the design and fabrication of precursor alloys are improved and optimized.Combining with diversified dealloying methods,the substrate-supported NPMs and hierarchically NPMs are successfully fabricated,realizing the multiple control over the macro shape/size and micro structure/composition.Moreover,the as-fabricated substrate-supported NPMs and hierarchically NPMs break the function limitations of traditional NPMs,exhibiting excellent mechanical tensile properties and unique structure function(combining high specific surface area with faster charge transfer behaviors),which could provide ideas for the design and fabrication of nanoporous metals with high activities and high structure/performance stabilities,and push forward their practical applications. |
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