Copper Mediated Hydrothermal Synthesis of Ultra Long Pentagonally Twinned Palladium Nanowires

Abstract

Palladium nanowires (Pd NWs) have attracted considerable attention due to applications in hydrogen sensing and heterogeneous catalysis. Several methods have been reported for the synthesis of Pd NWs including using chemical vapor transport, electrodeposition in porous membranes, electron beam lithography, and colloidal self-assembly; however, it has been challenging to produce large quantities. Hydrothermal methods have been reported recently for the production of high yields of Pd NWs using palladium (II) chloride as a metal precursor, deionized water as the solvent, and polyvinylpyrrolidone for the NW capping agent. Reported prior methods have not been reproducible. With the introduction of trace amounts of Copper (II) ions synthesis is possible and aspect ratios of >500 have been obtained. It is likely that the deionized water used in the synthesis contained trace amounts of copper from metal pipes, thus leading to the synthesis of PdNWs. Copper ions have been shown to act as effective oxygen scavengers during the aqueous synthesis and we postulate that oxidative etching of multiply pentagonally twinned palladium seeds must be avoided in order to achieve high yields of palladium nanowires. This research focuses on the trace addition of copper ions and improvement of the Pd NW synthesis.