Multi-scale morphological characterization of Ni foams with directional pores

Metallic foams show great potential as functional materials, due to their large surface area, low density, good gas permeability, and high strength-to-weight ratio. Owing to the inherent properties of Ni, including relatively high electrical conductivity, catalytic activity, and corrosion resistance, Ni foams are excellent candidate materials in energy applications such as electrodes for batteries and dye-sensitized solar cells, as well as current collectors in solid oxide fuel cells. In this study, we characterized Ni foams made by the freeze casting process using multi-scale morphological and structural characterization techniques, including X-ray computed tomography (XCT), scanning electron microscopy (SEM), and electron backscattered diffraction (EBSD) to study the structure of the Ni foams on the scale of several micrometers to a few millimeters. The multi-scale structural characterization results showed that the freeze casting method was successful in creating Ni foams with uniform directional pores, and the relative densities/solid area fraction and pore distribution of the Ni foams were uniform across different sample thicknesses, which can be fine-tuned by varying the concentration of NiO powder in the slurry during freeze casting.