Refinement of Nanoporous Copper: A Summary of Micro-Alloying of Au-Group and Pt-Group Elements

Abstract

The micro-alloying of 1 at% metals of Au-Group (Ag, Au) and the Pt-Group (Ni, Pd, Pt) with the Ti 60 Cu 40 amorphous alloy resulted in the formation of fine nanoporous copper (NPC) in the order of 628 nm. The smallest characteristic pore size of opencell nanoporous fcc Cu was 7 and 6 nm after dealloying the amorphous Ti 60 Cu 39 Pd 1 and Ti 60 Cu 39 Pt 1 precursor alloys for 43.2 ks in 0.03 M HF solution, while NPC had a pore size of 39 nm after dealloying the amorphous Ti 60 Cu 40 precursor alloy. On the basis of TEM micrographs, the refining factor increased approximately from 4 for the Ti 60 Cu 39 Ag 1 precursor alloy to 1780 for the Ti 60 Cu 39 Pt 1 precursor alloy. The refinement was attributed to the dramatic decrease in the surface diffusivity during dealloying. The refinement efficiency of the micro-alloying of the Pt-group elements was higher than that of the Au-group elements. The homogeneous distribution of additives in both of the amorphous precursor alloys and the final stabilized NPCs played a key role in refining the NPCs. This strategy may contribute to the fabrication of cost-effective nanoporous metals with a nanoporosity comparable to that of nanoporous Au, Pd and Pt catalysts.

Elaboration of Nanoporous Copper via Chemical Composition Design of Amorphous Precursor Alloys

“…The ribbon samples were fabricated by melt spinning with a dimension of 20 μm in thickness and 2 mm in width. The starting Ti 60 Cu 39 M 1 amorphous precursor alloys were treated under the free immersion condition for 43.2 ks in 0.03 M HF solution at 298 K. The detailed information of the experimental procedures has been supplied in the previous publications [27][28][29][30]. An X-ray diffractometer (XRD, Rigaku 4200) was employed to identify the change in the lattice constants, crystalline states of dealloyed alloys and microstructure of precursor alloys and dealloyed alloys.…”

“…The Cu adatoms diffused quickly in and out by themselves; however, the Au adatoms at the activated sites diffused out slowly and hardly ever diffused back to the NPC ligaments. Consequently, Au adatoms gradually accumulated outside the ligaments during the dealloying [27,30]. As a result, Au adatoms uniformly distributed outside the ligaments after dealloying for 43.2 ks via the hopping mechanism, as shown in Figure 5.…”

“…On the other hand, the grain sizes were reduced to 15 nm and 13 nm when the Pd and Pt were added into Ti 60 Cu 40 ribbons. The decrease in the grain sizes was considered to be due to the retardation of the self-diffusion of Cu adatoms by LSD elements [27,29,30]. The diffusion distance of Cu adatoms under free diffusion patterns is prevailed in a long-distance diffusion mode [2,5,10,[19][20][21].…”

“…On the other hand, the elaboration of NPCs is helpful for the enhancements of the catalytic performance and sensitivity for various gaseous phases or metallic ions. Effective ways to reduce the characteristic nanopore sizes have been reported to be dealloying at low temperature [23]; chemical composition design of the precursor alloys, for example, Ag-Au-Pt [24], Al-Pt-Au [25], Ti-Cu-Au [26,27], Ti-Cu-Ag [28], Ti-Cu-Ni [29], and Ti-Cu-Pd/Pt [30]; and modification of the solution chemistry by using organic acids [31] and by introducing the macromolecules of polyvinylpyrrolidone [32,33]. The chemical composition design is considered to be an effective way to change the surface diffusion and rearrangements of the adatoms of the noble elements in the precursor alloys since these noble elements take effect from inside to outside.…”

Ethanol-Mediated 2D Growth of Cu2O Nanoarchitectures on Nanoporous Cu Templates in Anhydrous Ethanol

“…Nanoporous noble metals with a high surface area and conductivity, such as Pt, Pd, Au, Ag, [ 26 , 27 , 28 ] have been fabricated via dealloying process. In order to reduce the cost of the nanoporous noble metals, many cost-effective metals with porous structures, such as Ni and Cu [ 29 , 30 , 31 ], have also been fabricated. The relative rough morphology with large nanopores and coarse ligaments restricts the potential application of nanoporous Cu in the catalytic and energy fields.…”