Structural Characterisation of Nanoporous Copper

Nanoporous metals are generally defined as metals with features in the pore structure in the range of 100 nm or less and are of significant interest due to their high surface areas and unique properties, which make them valuable for applications in catalysis, energy storage, and sensing. Nanoporous copper (np-Cu) has recently emerged as a promising alternative to more expensive nanoporous metals such as gold and platinum. In this study, np-Cu was prepared using a three-step process: (i) in-situ alloying of aluminium and copper by laser powder bed fusion (LPBF), commonly known as 3D laser printing, (ii) annealing the alloy at 530°C to promote phase stability and atomic diffusion, and (iii) de-alloying to selectively remove aluminium from the bulk alloy, leaving behind a porous copper structure. Despite changes in the composition during the de-alloying process, the domains within the alloy retained their spatial positioning and extent, preserving the structural integrity of the material. The properties of np-Cu were systematically characterized using various techniques. X-ray diffraction (XRD) was employed to examine the crystal structures, confirming the retention of the copper crystal lattice post-de-alloying, while X-ray fluorescence (XRF) spectroscopy provided an analysis of the chemical composition, verifying the effective removal of aluminium and purity of the copper. Surface topography and morphology were investigated using scanning electron microscopy (SEM), revealing a well-distributed network of nanopores. The pore size distribution and internal surface area were quantified using advanced techniques such as microcomputed tomography (-CT) and mercury intrusion porosimetry. These methods provided detailed insights into the material’s internal structure, confirming an internal surface area and a controlled pore size distribution. Overall, the three-step process used to synthesize np-Cu, involving in-situ alloying, annealing, and de-alloying, offers a versatile and scalable approach to producing nanoporous metals with controlled properties. The retention of the spatial arrangement of alloy domains throughout the de-alloying process ensures the stability of the nanoporous structure, making np-Cu a promising material for a variety of advanced applications. The comprehensive characterization of its morphology, crystal structure, and surface properties provides valuable insights into its potential use in fields such as catalysis, energy storage, and sensing technologies.