Synthesis,Properties Of Flexible Nanoporous Metals And Their Composites

Nanoporous metals have attracted great attention in flexible electronics due to their unique three-dimensional（3D）bicontinuous open porous structure with a large specific surface area,high porosity,good thermal and electric conductivity,as well as other excellent physicochemical properties.Recently,most of the research focuses on controlling the microstructure and morphology of nanoporous metals and improving their chemical/electrochemical properties.However,the research on improving the strength and toughness of nanoporous metals,and solving its macroscopic brittleness is not enough.The macroscopic brittleness will easily cause the damage,fracture and crushing of nanoporous metals under the external force loading,which results the material are easily failed in long-term service.It also greatly limits their further development and commercial application in flexible electronics.Therefore,this paper systematically studied the main reasons that affect the mechanical properties of nanoporous metal materials.In order to design and prepare the nanoporous metals with excellent mechanical properties,we attempted to improve the connectivity of porous structure and enhance the intrinsic strength of the ligaments structure.The fracture and deformation mechanism of nanporous metal were studied in detail,and its applications in biosensors and flexible energy storage were finally discussed.1.Nanoporous metals with good ligaments were prepared by phase etching method to improve the mechanical properties of nanoporous metals.Nanoporous Ag（NP Ag）prepared by selective phase etching the bi-phased Cu-Ag-La nanocrystalline alloy precursors has better ligaments connectivity than NP Ag prepared by dealloying single-phase alloy precursors.The formation mechanism of highly continuous porous ligaments structure by phase etching bi-phased nanocrystalline alloy was studied.The Cu phase was selectively corroded from the alloy precursor and the Ag phase was retained to form the continuous NP Ag ligament structure.The effect of NP Ag structure（ligament continuity/microcrack）on the mechanical properties,especially the flexibility/brittleness was studied.The tensile strength and nanohardness of NP Ag with high ligaments connectivity were 68 MPa and 0.208 GPa,respectively.The tensile strength and nanohardness of NP Ag with low ligaments connectivity were 32MPa and 0.128 GPa,respectively.The degree of ligaments connectivity of NP Ag affects its strength and hardness,but it has less effect on its flexibility/brittleness.The tensile strength and nanohardness of NP Ag with crack defects were 9 MPa and 0.018GPa,respectively,which are much lower than that of NP Ag without crack defects.The rapid propagation and expansion of microcracks in NP Ag under external forces leads to the destruction of the porous structure,which makes it exhibit macroscopic brittleness.By controlling the crystal structure of Cu_60-xAg₄₀La_x（x=0,3,6 at.%）alloy precursor,the microstructure of NP Ag was controlled.And then,the mechanical properties of NP Ag was controlled,such as strength,hardness and fracture toughness.The flexible energy storage electrode was prepared by using NP Ag as a current collector and high-performance Co（OH）₂nanoplates as electrode material,which showed good supercapacitor performance.2.The intrinsic strength of ligaments was enhanced to improve the mechanical properties of nanoporous metals.By selective etching the bi-phased Cu-Zr-Y-Al metallic glass（MG）,the nanoporous Zr-Cu-Al MG（NP Zr-Cu-Al MG）with high ligaments connectivity was formed.The tensile strength and nanohardness of NP Zr-Cu-Al MG were 240.7 MPa and 1.27 GPa,respectively.After further dealloying the NP Zr-Cu-Al MG,the uniform Cu metal layer were formed on the surface of Zr-Cu-Al MG ligament.The tensile strength and nanohardness of NP Cu@Zr-Cu-Al MG were 143.9 MPa and 0.79 GPa,respectively,which were much higher than that of the other nanoporous metals.The Zr-Cu-Al MG matrix in Cu@Zr-Cu-Al MG ligaments showed high intrinsic strength,which could inhibit the initiation and propagation of cracks in NP Cu@Zr-Cu-Al MG,and then the NP Cu@Zr-Cu-Al MG could exhibit excellent mechanical properties.The Cu metal layer on the Zr-Cu-Al MG ligaments improved its electrical conductivity.The NP Cu@Zr-Cu-Al MG can be directly used as the flexible electrode material,which showed good supercapacitor and glucose sensor performance.