A group of Korean researchers have developed a new technique for producing metal foams with highly ordered, sub-micrometre-scale pores.
Nanoporous foams have been a buzz word in materials research over the last decade, but much of the work has focused on organic or inorganic materials. Until recently, producing metallic foams with reliable pore size remained elusive. With their high surface area, such foams have been proposed for use in a range of applications, from sensors to high-efficiency heat-exchangers.
AFM images of (a) the top morphology of the nanoporous Cu foam taken at a low magnification and (b) the smooth surface of a zoomed-in Cu strut with an average surface roughness (Ra) ~13 nm.In a recent issue of Materials Letters, a Korean research group presented a new technique for producing copper and nickel foams that display sub-micrometre-scale, highly-ordered pores. They believe that these foams could be promising electrode materials for energy storage systems, such as the next generation of batteries.
To produce these foams, the team developed a modified electroless plating technique, based on a proximity-field nanopatterned (PnP) polymer template. The polymer template was produced in-house, and activated so that it became catalytic. The template was then plated with either nickel of copper (to a thickness of 45 – 51 nm), resulting in foams with uniform pore size or up to 330 nm in diameter.
The researchers, who published the work in Materials Letters [doi:10.1016/j.matlet.2014.05.043], believe that their technique offers a number of advantages over conventional techniques – by using the polymer template, it can produce highly ordered submicron pores in both Ni and Cu foams, and the resulting foams can be several tens of microns in thickness. The use of electroless plating also has the added benefit of preventing corrosion of the metal in the foam.
Mechanical strength is also a key consideration for all battery materials, and so the strut structure of the Cu and Ni foams was also analysed, and was found to outperform other types of metallic foams fabricated by the conventional de-alloying process.
The structural and mechanical properties of the metal foams render them suitable for practical applications, such as for use as electrodes in batteries, dye-sensitised solar cells, or fuel cells.
Materials Letters (2014) doi:10.1016/j.matlet.2014.05.043
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