Fabrication And Electrochemical Properties Of Nanoporous Metals And Their Composities Based On Cu-Zr-Ag Metallic Glass Precursors

In this dissertation,Cu-Zr-Ag ternary amorphous alloys were used as the precursors to prepare nanoporous metals?NPM?by a combination of rapid solidification and free dealloying.Nanoporous copper-silver bimetal?NP-CuAg?and nanoporous silver?NP-Ag?can be prepared by dealloying Cu₄₀Zr₅₀Ag₁₀ and Cu₄₀Zr₄₀Ag₂₀ amorphous alloys in HF or HF+HNO₃ mixed solution.The dealloyed products of Cu₄₀Zr₅₀Ag₁₀ and Cu₄₀Zr₄₀Ag₂₀amorphous alloys in HF solution were denoted as NP-CuAg1 and NP-CuAg2,respectively.The NPM-supported MnO₂ composite electrode materials were prepared by chemical precipitation with reduction of KMnO₄ by ethanol.This work systematically studies the dealloying process of Cu-Zr-Ag ternary amorphous alloy and the influence of the precursor composition and dealloying parameters on the nanoporous structure of the dealloyed products.Moreover,the capacitance performances of NPM/MnO₂ composites with different substrate materials are investigated.The basic relationship among precursor alloy/dealloying parameters,microstructure and electrochemical performance is established in this work,which guides for developing new electrode materials with excellent capacitance for supercapacitors.The results obtained are summarized as follows:Firstly,the initial alloy composition has a great influence on the micromorphology of the dealloyed products.Cu₄₀Zr₅₀Ag₁₀ and Cu₄₀Zr₄₀Ag₂₀ amorphous alloys were dealloyed in HF solution under the same conditions to obtain NP-CuAg1 with both nano-pores and triangular micro-pores,and NP-CuAg2 with uniform nanoporous structure,respectively.The controllable preparation of NP-CuAg2with ligament size range of 55²00 nm was successfully achieved by controlling the parameters of dealloying process.Secondly,NP-Ag with three-dimensional bi-continuous homogeneous porous architecture was prepared by one-step dealloying Cu₄₀Zr₄₀Ag₂₀amorphous alloy in 0.5 M HF+0.67 M HNO₃ mixed solution,and NP-Ag exhibits finer ligaments/holes as compared to NP-CuAg.The electrochemical properties of the NPM/MnO₂ composites were investigated by cyclic voltammetry and galvanostatic charge/discharge measurements.The results show that NPM/MnO₂ composites exhibit excellent capacitance performance.The specific capacitance increases with the increase of the Ag content in the substrate materials.The electrode composites with NP-CuAg1,NP-CuAg2 and NP-Ag as substrates display specific capacitance values of 449.03 F/g,486.48 F/g and 520.41 F/g,respectively,at the scanning rate of 2 mV/s.The results of the EIS test show that with the increase of the Ag content in the electrode substrate material,NPM efficiently leads to the lower charge transfer resistance(R_ct)and the higher electrical conductivity of the composite.The NP-Ag/MnO₂composite possesses the optimal capacitance performance,resulting from the finer and uniform porous morphology of NP-Ag,excellent electrical conductivity,and the synergistic effect of Ag with the MnO₂ electroactive material in the electrode reaction.The NP-Ag/MnO₂ composite has a capacitance of 520.41 F/g at the scanning rate of 2 mV/s,which is 1.87 times that of the pure MnO₂ electrode.Moreover,it displays excellent cycle stability,the specific capacitance still remains 100.44%of the initial capacity value after5000 cycles.