Casting of high surface area electrodes enabled by low-temperature welding of copper nanoporous powders and nanoparticles hybrid feedstocks

Abstract

Nanoporous metallic powders are proposed as electrodes for hydrogen production, current collectors in batteries, or active material in propellants to overcome limitations in reaction kinetics of their bulk solid counterpart. However, their consolidation into 3D parts via powder metallurgy while maintaining high mechanical performance is limited by their thermodynamic instability during sintering and poor flowability. This paper demonstrates the synthesis of spherical nanoporous copper powders (PCu) via dealloying of Cu-Al gas-atomized precursors with high-throughput (i.e., 0.1 kg/hr), moderate flowability (i.e., Carney flowrate of 32.9 s/50 g), moderate-oxygen content (i.e., < 12 at.%), high-surface area (∼12 m2/g) and free of precipitates. The nanoscale weldability of hybrid feedstocks composed of PCu (65.5 – 91.2 vol.%) and copper nanoparticles (8.8 – 34.5 vol.%) were harvested to sinter them at temperatures as low as a third of its melting point and overcome the metastability of PCu to preserve its high-surface area. Open-die casting in reducing atmospheres was employed at temperatures between 300 – 700 °C resulting in parts with ultimate compression strength of 3.6 – 17.8 MPa while forming electrically conductive solids with preserved nanoporosity (i.e., pore size 24 – 36 nm). Such feedstocks may be integrated with powder-based manufacturing processes such as powder injection molding and additive manufacturing to produce complex architectures.