Morphological Control of Nanoporous Copper Formed from Conversion Reaction Synthesis

Abstract

The pore architecture of nanoporous copper (NP-Cu) plays a vital role in its technological applications. The synthesis of NP-Cu by the conversion reaction has been reported, where an ionic Cu precursor (salt or oxide) is chemically reduced with n-butyllithium to form a Cu metal nanocomposite, from which the Li-containing product is removed to form NP-Cu. Anions in the Cu compound precursors significantly affect the size of Cu in the nanocomposite due to the effect of lithium salt on Cu diffusion. Thermal annealing of the nanocomposites reveals that the activation energy for diffusion correlates with the melting point of the lithium salt, which is used as a proxy for their tendencies of forming defects, indicating that Cu diffusion takes place through the bulk phase of the salt rather than the Cu/salt interfaces. This experimentally observed behavior is consistent with the results from density functional theory calculations. Further, doping the lithium salt with Mg2+ increases the defect concentration and facilitates enhanced Cu diffusion. The choice of anion in the Cu salt precursor thus provides an effective tool to enable control of the nanoscale size of Cu and the resultant NP porosity.