Easy access to Cu0 nanoparticles and porous copper electrodes with high oxidation stability and high conductivity

Cu-0 nanoparticles with a diameter of 20 nm and a narrow size distribution are obtained by NaBH4-induced reduction of CuCl2 center dot 2H(2)O in diethylene glycol. The course of the reaction essentially involves an intermediate formation of copper citrate (Cu-3(citrate)(2)center dot nH(2)O) nanoparticles to control the nucleation of almost monodisperse and non-agglomerated Cu-0 nanoparticles. The as-prepared and citrate-capped Cu-0 nanoparticles turn out as surprisingly stable against air oxidation. When left in contact with air for 14 months, the Cu-0 powder samples and thin films do only show minor oxide impurities. Even short-time heating to 120 degrees C in air is tolerable. Via simple solvent evaporation, porous Cu-0 thin-films are prepared on corundum substrates that exhibit a very low resistivity of 3 x 10(-4) U cm after sintering at 220 degrees C in forming gas (N-2 : H-2 = 90 : 10). With these features the as-prepared, citrate-capped Cu-0 nanoparticles become highly relevant to thin-film electronics, thin-film sensors and highpower batteries.