The electrochemical response of single crystalline copper nanowires to atmospheric air and aqueous solution

In this paper, single crystalline copper nanowires (CuNWs) have been electrochemically grown through anodic aluminum oxide (AAO) template. The environmental stability of the as-obtained CuNWs in both 40 % relative humidity (RH) atmosphere and 0.1 M NaOH aqueous solution have been subsequently studied. In 40 % RH atmosphere, a uniform compact Cu2O layer is formed as a function of exposure time following the logarithmic law and epitaxially covers the CuNW surfaces. It was also found that the oxide layers on CuNWs are sequentially grown when subject to the cyclic voltammetry measurement in 0.1 M NaOH solution. An epitaxially homogeneous Cu2O layer is initially formed over the surface of the CuNW substrates by solid-state reaction (SSR). Subsequently, the conversion of Cu2O into epitaxial CuO based on the SSR takes place with the increase of applied potential. This CuO layer is partially dissolved in the solution forming Cu(OH)2, which then redeposited to the CuNW surfaces (i.e. dissolution-redeposition (DR) process) giving rise to a mixed polycrystalline CuO/Cu(OH)2 layer. The further increase of applied potential allows the complete oxidation of Cu2O into CuO to form a dual-layer structure (i.e. CuO inner layer and Cu(OH)2 outer layer) with random orientations through an enhanced DR process.