Fabrication And Properties Of Nanoporous Metals And Their Composites Based On Metallic Glass Precursors

Nanoporous metals as a representative class of functional materials have attracted extensive attention owing to their high surface area,low density,high permeability,high electric/thermal conductivity and tunable nanostructure,which endow their great potential applications for catalysis,sensor and energy storage.To date,most nanoporous metals have been fabricated by dealloying crystalline alloy precursors,typically solid solution alloys.Nevertheless,considering the fact that metallic glasses have advantages for obtaining uniform nanoporous structure with tunable porosity due to their monolithic amorphous microstructure and wide composition range,in this research,several new-type nanoporous metals and their composites with tunable nanoporosity and excellent performance have been designed and fabricated by dealloying two kinds of selected glassy precursors,i.e.,Ag-and Cu-based metallic glasses.The formation mechanism and service performances of these nanoporous materials have been systematically investigated.The thesis mainly includes the following contents:(1)Fabrication of nanoporous silvers(NPSs)by dealloying Ag-based glassy precursors and their surface enhanced Raman scattering(SERS)properties.Ag-Mg-Ca metallic glasses were selected as precursors to fabricate 3D NPS with tunable nanoporosity(pore size:25?200 nm).By systematically investigating the dynamic evolution of pore characteristics with precursor compositions and dealloying conditions,the correlation between nanoporosity and dealloying parameters was successfully established.Formation mechanism of the nanoporous structure was also revealed,which mainly involves:the dissolution of active Mg and Ca elements from the glassy precursor and the surface diffusion of Ag atoms at the glassy precursor/solution interface.Further investigations show that the growth of Ag ligaments is a thermally-activated diffusion process,which can be well described by the classical model of crystal growth.The resultant NPS can be used as high-performance SERS substrate,exhibiting the highest SERS enhancement factor of 7.59 × 108,which is close to the detection level of a single molecule.Meanwhile,smaller pore sizes could lead to stronger SERS enhancement.(2)Development of electrochemical supercapacitors with uniform NPS network.By plating the MnO2 nanocrystals into the NPS matrix,the composite electrode was fabricated,which exhibits an ultrahigh specific capacitance(1088 F/g)of the plated active MnO2,?80%of the theoretical value,due to the fast ionic conduction and excellent electron-proton transport.The high specific capacitance(-384 F/g)and long operating lifetime of the nanocomposite make it a promising candidate as electrode material in high-performance electrochemical supercapacitor.(3)Bendable nanoporous copper(NPC)thin films with tunable thickness and pore features.Uniform NPC films with a tunable thickness in the range of?230 nm to?2.2 ?m were fabricated by surface chemical dealloying Cu-Zr-Al metallic glasses.Effects of the dealloying condition on the nanoporosity and thickness of the resultant NPC thin film were systematically investigated.The brittle-to-ductile transition was found to be dependent on the thickness of films,i.e.,the NPC becomes flexible as its thickness reduces below?2.2 ?m.This bendable nanoporous thin film could solve the problem of the brittleness of NPC and is promising for functional applications in micro/nano electromechanical systems.(4)Development of Cu(OH)2 nanograss array decorated NPC hybrid electrode for electrochemical glucose sensing.Hierarchical Cu(OH)2 nanowire array@NPC composite was fabricated by alkaline oxidation of NPC film in the(NH4)2S2O8 and NaOH aqueous solution.The inexpensive nanocomposite exhibits outstanding electrocatalytic activity for the glucose detection,including an ultrahigh sensitivity of?2.09 mA cm-2·mM-1,a wide linear dynamic range from 0.2 to 9 mM,remarkable low detection of 197 nM(S/N=3),fast response time of?1 s and excellent long-term stability,which have great potential to be commercialized for applications in quick blood sugar detection.(5)Fabrication of CuO nanowire array modified nanoporous Cu2O nanocomposites and their properties.Sandwich nanoporous Cu2O composite integrated with uniform CuO nanowire arrays was fabricated by heating the NPC thin film at 500 ? in air.The nanostructured electrode was evaluated for electrochemical glucose detection and the results show that the novel material exhibits reliable electrocatalytic activity towards the oxidation of glucose,i.e.,a high sensitivity of 1.95 mA cm-2 ·mM-1,a wide linear dynamic range from 0.1 to 6 mM and a low detection limit of 1 ?M(S/N=3).The hierarchical nanocomposite can also be employed as catalyst for degradation.Due to its high internal surface area,this material exhibits superior oxidation degradation performance for dyes than that of commercial CuO nanoparticles.