Multigram Synthesis of Cu-Ag Core–Shell Nanowires Enables the Production of a Highly Conductive Polymer Filament for 3D Printing Electronics

This article reports a synthesis that yields 4.4 g of Cu nanowires in 1 h, and a method to coat 22 g of Cu nanowires with Ag within 1 h. Due to the large diameters of Cu nanowires (≈240 nm) produced by this synthesis, a Ag:Cu mol ratio of 0.04 is sufficient to coat the nanowires with ≈3 nm of Ag, and thereby protect them from oxidation. This multigram Cu-Ag core–shell nanowire production process enabled the production of the first nanowire-based conductive polymer composite filament for 3D printing. The 3D printing filament has a resistivity of 0.002 Ω cm, >100 times more conductive than commercially available graphene-based 3D printing filaments. The conductivity of composites containing 5 vol% of 50-µm-long Cu-Ag nanowires is greater than composites containing 22 vol% of 20-µm-long Ag nanowires or 10-µm-long flakes, indicating that high-aspect ratio Cu-Ag nanowires enable the production of highly conductive composites at relatively low volume fractions. The highly conductive filament can support current densities between 2.5 and 4.5 × 10⁵ A m⁻² depending on the surface-to-volume ratio of the printed trace, and was used to 3D print a conductive coil for wireless power transfer.