Nanoporous Ni and Ni-Cu Fabricated by Dealloying
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1228-KK06-02
Nanoporous Ni and Ni-Cu Fabricated by Dealloying Masataka Hakamada,1 Yasumasa Chino1 and Mamoru Mabuchi2 1
Materials Research Institute for Sustainable Development, National Institute of Advanced Industrial Science and Technology (AIST), 2266-98 Anagahora, Shimoshidami, Moriyama, Nagoya 463-8560, Japan 2 Graduate School of Energy Science, Kyoto University, Yoshidahonmachi, Sakyo, Kyoto 6068501, Japan ABSTRACT Metallic nanoporous architecture can be spontaneously attained by dealloying of a binary alloy. The nanoporous architecture can be often fabricated in noble metals such as Au and Pt. In this study, nanoporous Ni, Ni-Cu are fabricated by dealloying rolled Ni-Mn and Cu-Ni-Mn alloys, respectively. Unlike conventional Raney nickel composed of brittle Ni-Al or Cu-Al intermetallic compounds, the initial alloys had good workability probably because of their fcc crystal structures. After the electrolysis of the alloys in (NH4)2SO4 aqueous solution, nanoporous architectures of Ni and Ni-Cu with pore and ligament sizes of 10–20 nm were confirmed by scanning electron microscopy and transmission electron microscopy. X-ray diffraction analyses suggested that Ni and Cu atoms form a homogeneous solid solution in the Ni-Cu nanoporous architecture. The ligament sizes of nanoporous Ni and Ni-Cu were smaller than that of nanoporous Cu, reflecting the difference between diffusivities of Ni and Cu at solid/electrolyte interface. Ni can reduce the pore and ligament sizes of resulting nanoporous architecture when added to initial Cu-Mn alloys. INTRODUCTION Nanoporous metals having pore and ligament sizes of nanometer order can be fabricated by dealloying (or electrochemically etching) binary alloys [1,2]. Recent studies involving dealloying have been concentrated on nanoporous gold fabricated by dealloying Au-Ag alloy [3– 7] during which the less noble silver dissolves in the electrolyte such as nitric acid. Nanoporous metals other than Au can also be fabricated through dealloying; for example, Pugh et al. [8] and Liu et al. [9] fabricated nanoporous platinum by dealloying Pt-Cu alloy. Nanoporous Pd can be also fabricated by dealloying of Pd-Co [10,11] and amorphous Pd-Ni-P alloys [12]. Nanoporous nickel can be obtained by the alkali leaching of aluminum from Ni-Al Raney nickel [13] and has been widely used in catalytic applications [14,15]. The alkali leaching corresponds to dealloying without the application of an electrochemical potential. In the same manner, Cu-Al Raney copper can be alkali-leached to fabricate a nanoporous copper catalyst [16]. However, the porous structure derived from Raney nickel and copper is irregular [15,17] probably due to Ni-Al and Cu-Al intermetallics with their specific compositions. The brittle intermetallics also limit the application of nanoporous nickel and copper to the powder form. If the starting alloy is ductile, the desired macroscopic shape of the resulting nanoporous nickel and copper can be formed by plastic deformation of the starting alloy, thus widening the range of forms
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