Formation of CuOx Nanowires by Anodizing in Sodium Bicarbonate Solution

Abstract

Mechanism of copper nanostructuring by oxides and hydroxide formation during anodizing is not fully understood. At the same time, the search for novel copper anodizing regimes and electrolytes is ongoing due to multiple potential applications. In this work copper anodizing in two electrode setups, in stirred 0.01 M solution of NaHCO3 at 20 °C and at voltages ranging from 5 to 40 V was explored. The morphology and composition of prepared materials were studied using FE-SEM imaging and XRD measurements. Anodizing at potentials in a range of 15–30 V led to formation of nanowires composed of crystalline Cu2O, CuO, Cu(OH)2 and malachite Cu2CO₃(OH)2. The latter was formed due to anion incorporation from the electrolyte. The diameter of nanowires strongly depended on the applied voltage, and was 35 ± 6 nm for samples prepared at 15 V, and 45 ± 9 nm for 30 V. At higher applied voltages oscillations of current density were observed, suggesting partial delamination of the formed oxidized layer, with subsequent self-healing.

Fabrication, Characterization and Photocatalytic Activity of Copper Oxide Nanowires Formed by Anodization of Copper Foams

“…XRD patterns also confirm the incorporation of electrolyte anions into the formed products of anodizing. Reflexes from (111) and (221) planes of malachite, Cu 2 CO 3 (OH) 2 were noticed, which is in line with previously reported research on planar copper anodizing in 0.1 M K 2 CO 3 [9] and 0.01 M NaHCO 3 [22]. Moreover, FTIR experiments also confirmed the presence of C-O bondings (Figure 2).…”

“…It is worth noting that in some cases, the anodically formed cupric hydroxide is amorphous; in other cases, it can be crystalline. Obtained results are in line with planar copper anodizing in 0.1 M K 2 CO 3 [9] and 0.01 M NaHCO 3 [22].…”

“…Paramelconite, Cu 4 O 3 , an oxide with mixed oxidation states of copper, was also detected within the XRD experiments; however, reflex from only (103) plane was distinct in the XRD patterns. Detection of this oxide is quite unique when compared to other reports; nevertheless, it was reported to be obtained by copper anodizing in 0.1 M K 2 CO 3 [9] and 0.01 M NaHCO 3 [22].…”

“…This leads to the formation of Cu(OH) 2 , and annealing 3 h at 150 • C or 200 • C leads to hydroxide decomposition and formation of crystalline tenorite and cuprite [22]. Paramelconite, Cu 4 O 3 , an oxide with mixed oxidation states of copper, was also detected within the XRD experiments; however, reflex from only (103) plane was distinct in the XRD patterns.…”

“…Copper oxides can easily be formed by the thermal oxidation of copper at elevated temperatures [20]. Recently, nanostructured copper oxides such as nanowires for various technological applications have been prepared [21][22][23][24].…”