Multiscale Morphology of Nanoporous Copper Made from Intermetallic Phases

Abstract

Many application-relevant properties of nanoporous metals critically depend on their multiscale architecture. For example, the intrinsically high step-edge density of curved surfaces at the nanoscale provides highly reactive sites for catalysis, whereas the macroscale pore and grain morphology determines the macroscopic properties, such as mass transport, electrical conductivity, or mechanical properties. In this work, we systematically study the effects of alloy composition and dealloying conditions on the multiscale morphology of nanoporous copper (np-Cu) made from various commercial Zn-Cu precursor alloys. Using a combination of X-ray diffraction, electron backscatter diffraction, and focused ion beam cross-sectional analysis, our results reveal that the macroscopic grain structure of the starting alloy surprisingly survives the dealloying process, despite a change in crystal structure from body-centered cubic (Zn-Cu starting alloy) to face-centered cubic (Cu). The nanoscale structure can be controlled by the acid used for dealloying with HCl leading to a larger and more faceted ligament morphology compared to that of HPO. Anhydrous ethanol dehydrogenation was used as a probe reaction to test the effect of the nanoscale ligament morphology on the apparent activation energy of the reaction.

Ligament Evolution in Nanoporous Cu Films Prepared by Dealloying

“…9,10 In addition, the pH value, kind of electrolyte, and applied potential can be adjusted to the structure of spongelike materials by controlling the surface diffusion of the remaining noble metal in the presence of adsorbing ions or oxide-based passivation layers. 11,12 This enables the tailoring of the characteristic properties like ligament size, pore size, and chemical composition of the np materials over a broad length scale. 13−15 Although numerous research works have already been performed, there is still a need for understanding of the evolution of porous materials by dealloying.…”

“…In particular, during the dissolution of a less noble metal, the surface diffusion process of the remaining noble metal leads to the formation of nanosized ligaments and pores. Thus, the dealloying processes depend on the kinetics of the dissolution of the less noble metal and of the surface diffusion of the remaining noble metal as well as the mass transport processes at the interface between the electrolyte and the alloyed surface. , In addition, the pH value, kind of electrolyte, and applied potential can be adjusted to the structure of spongelike materials by controlling the surface diffusion of the remaining noble metal in the presence of adsorbing ions or oxide-based passivation layers. , This enables the tailoring of the characteristic properties like ligament size, pore size, and chemical composition of the np materials over a broad length scale. − …”

Patterning Cu nanostructures tailored for CO2 reduction to electrooxidizable fuels and oxygen reduction in alkaline media

“…18 Although CuNSs are unstable in acidic environments under anodic polarization or unbiased conditions, 19 their anodic treatment in alkaline solutions causes the formation of CuO x nanostructures exhibiting catalytic activity towards electrooxidation of various organic substances, such as L-tyrosine, 20 glucose, 21,22 hydrazine, 22 and water. 23,24 Even though there are a number of successful applications of noble metal (Pt and Pd) based nanocatalysts to electrochemical conversion of CO 2 , [25][26][27] copper is the most promising catalyst for the CO 2 RR yielding valuable, high energy density products such as hydrocarbons, [28][29][30][31] alcohols, 28,29,32 formic acid and other carbonyls. 28,29,[32][33][34][35] It was demonstrated that the morphology and therefore the electrocatalytic properties of Cu nanostructures towards the CO 2 RR can be tuned by the addition of phosphate and the electrodeposition potential 35 or appropriate selection of the Cu complex precursor.…”

“…For electrocatalysis the most useful are CuNSs deposited on conductive surfaces. This can be achieved by laser ablation of copper surfaces, 13,41 plasma etching, 19 dealloying, 30,31 electrochemical polishing, 53 thermal annealing, 54 or electrodeposition. 10,18,20,22,43,55,56 Gowthaman and John demonstrated that the applied substrate potential during Cu electrodeposition affects the geometry of the obtained deposit.…”

Nanoporous Copper-Nickel – Macroscopic bodies of a strong and deformable nanoporous base metal by dealloying

“…As Cu is rather electropositive, it is a natural candidate as an affordable material for dealloying processes based on corrosion in aqueous media. Nanoporous Cu has been prepared by dealloying from various alloys compositions that include -next to Cu -Mn [6,29,30], Al [31,32] and Zn [32,33], respectively. However, while Cu in clean air forms a thick oxide layer that passivates the surface [34], Cu and its oxides are readily dissolved in numerous electrolytes when oxygen is present [35].…”