Easy access to Cu0nanoparticles and porous copper electrodes with high oxidation stability and high conductivity

Abstract

Cu⁰ nanoparticles with a diameter of 20 nm and a narrow size distribution are obtained by NaBH₄-induced reduction of CuCl₂·2H₂O in diethylene glycol. The course of the reaction essentially involves an intermediate formation of copper citrate (Cu₃(citrate)₂·nH₂O) nanoparticles to control the nucleation of almost monodisperse and non-agglomerated Cu⁰ nanoparticles. The as-prepared and citrate-capped Cu⁰ nanoparticles turn out as surprisingly stable against air oxidation. When left in contact with air for 14 months, the Cu⁰ powder samples and thin films do only show minor oxide impurities. Even short-time heating to 120 °C in air is tolerable. Via simple solvent evaporation, porous Cu⁰ thin-films are prepared on corundum substrates that exhibit a very low resistivity of 3 × 10⁻⁴ Ω cm after sintering at 220 °C in forming gas (N₂ : H₂ = 90 : 10). With these features the as-prepared, citrate-capped Cu⁰ nanoparticles become highly relevant to thin-film electronics, thin-film sensors and high-power batteries.