This presentation will report the first electrochemical studies of Cu nanowire growth utilizing Cu(100) and Cu(111) single crystal electrodes as proxies for the sides and ends of Cu nanowires, respectively. These studies show that, rather than acting as a capping agent, ethylenediamine selectively inhibits the formation of Cu oxide on Cu(111), and thereby selectively promotes reduction of Cu ions onto Cu(111). Reduction of Cu ions onto Cu(100) is inhibited due to the formation of a Cu oxide layer in the highly basic (15 M NaOH) reaction solution.7In contrast, the alkylamine-based synthesis of Cu nanowires takes place in a solution with a neutral pH, and the formation of Cu oxide does not play a role in anisotropic growth. Instead, preliminary results indicate alkylamines act as a capping agent by increasing the charge transfer resistance on Cu(100) to a greater extent than on Cu(111). These results demonstrate that single crystal electrochemistry can be a powerful tool for elucidating the facet-selective chemistry of capping agents in nanostructure syntheses, and can provide a rational basis for the discovery of novel capping agents for directing anisotropic growth.
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Figure. 1. The image of Cu nanowires synthesized in an aqueous solution consisting of 15 M NaOH, 4.74 mM Cu(NO3)2, 70 mM EDA, and 10.5 mM N2H4. The reaction temperature and time were 70°C and 20 min, respectively.