The Study Of Nanoporous Copper/Copper Oxides: Towards Fabrication, Performance And Mechanism

Because of their unique 3D continuous ligaments-pores structure, large specific surface area and distinctive physical and chemical properties, nanoporous（np-） metals have shown tremendous potential in a wide range of applications, such as catalyzing, sensing, actuating and energy transforming and storing. Dealloying has been demonstrated to be a simple and effective strategy to fabricate nanoporous metals（e.g. np-Au, np-Pt and np-Cu etc.） from many precursor alloys. Benefiting from its high reactivity and richer storage than Au, Pt and Pd, the study on np-Cu is academically and practically meaningful. So forth, corrosion conditions through which ligaments-pores structures can be tuned have been well studied, while the explorations of precursors are rare especially the alloying method as well as the role of the applied parameters during alloying on the dealloying products. Al-Cu alloy precursors with various components were prepared through sintering method under well controlled parameters and nanoporous copper/copper oxides with tunable microstructures were obtained after chemical dealloying. The relationships between microstructure of sintered alloys studied using molecular dynamic（MD） simulating sintering process and the adsorption behaviors of copper clusters investigated through density functional theory（DFT） were studied to identify the mechanism of formation of the oxides. In addition, a group of recommended alloying parameters was identified from which a mixture of Cu/Cu₂O/CuO that exhibited an excellent initial sonocatalytic degradation efficiency to methyl orange.The pressure, sintering temperature and holding time play significant roles in the formation of Al-Cu alloy precursors. For Al₆₇Cu₃₃ alloy, Al₄Cu₉ and AlCu phases appear in the alloys when sintering temperature is as low as 400 ℃, and elongation of holding time to 60 and 120 min would generate more Al₂Cu phase and less Al₄Cu₉ phases. When holding time is fixed, higher sintering temperature would make more Al₂Cu phase and less Al₄Cu₉ and AlCu phases. A small pressure（300 MPa） is good for the atom diffusion and the formation of Al₂Cu phase. As for Al₈₅Cu₁₅, only a minor AlCu phase and a majority of Al₂Cu phase are formed when a slight higher temperature of 430 ℃ is applied. When temperature is enhanced to 500 ℃ and sintering processes are prolonged, only Al and Al₂Cu phases are formed.Al₂Cu phase is fully dealloyed in 20 wt% NaOH while AlCu and Al₄Cu₉ phases corrodes at a relative slow rate so that they are detected in some dealloying samples.Cu and Cu2 O are found in all products from dealloying Al₆₇Cu₃₃ alloys while CuO is found in some certain cases. And the products from dealloying Al₈₅Cu₁₅ alloys also vary from one to another. In addition, the products are mainly composed of nanostructured particles and nanoplates in all cases, which is different from previous reports in which 3D continuous ligaments-pores were usually seem. Besides, hierarchical features in products form dealloying Al₈₅Cu₁₅ alloys suggest that microstructure in precursor would inherit during dealloying.Orientation growth during sintering is identified from XRD and electrochemical corrosion data. MD results indicate that Al diffuse faster than Cu atoms and their inter-percolation are determined by chemical potentials which are determined by the atoms ratios of Al/Cu. Namely, when Al/Cu ≤1, they finally form a Cu（core） @ Al（shell） structure and the elongation of simulating time to 2000 ps does not contribute to further inter-percolation of Al and Cu. When Al/Cu is large(5.36 here, which was close to that of Al₈₅Cu₁₅), Al would readily diffuse to the inner part of Cu and arrive at diffusion balance within 1000 ps. Cu clusters with various sizes distribute in Al-Cu and thereby form Cu-rich and Al-rich areas.Combining energies of Cun and O was 1.5¹.9 times larger than that of Cun and OH-. And O is mainly adsorbed on t he most（or nearly most） reactive Cu atoms on t op-type, bridge-type or three-fold hollow sites. In addition, Cun-O clusters diffuse much slower than Cu atoms by four orders of magnitudes. And this low diffusion race may allow Cu clusters adsorb more O and form the precursors of the copper oxides.Dealloyed product（np-Cu/oxides, 0.4 g/L） exihibit excellent sonocatalytic catalysis performance to Methyl Orange. A group of recommended alloying parameters is therefore identified: namely, a pressure of 300 MPa, sintering temperature of 500 ℃ and holding time of 60 min.