Effects of complex agents on the anodic deposition and electrochemical characteristics of cobalt oxides

The anodic deposition rate of cobalt oxide from CoCl2·6H2O is strongly affected by the type of complex agents (acetate ion (AcO−), citrate ion, EDTA) added into the deposition solutions. The oxidation potential of CoCl2·6H2O, examined by linear sweep voltammetry (LSV), is negatively shifted from ca. 1.1 V to about 0.8, 0.5, and 0.2 V by adding AcO−, citrate ion, and EDTA, respectively. The deposition rate of cobalt oxide is found to depend not only on the coordinating strength between Co and ligands but also on the conversion rate of the Co–L complexes (L: ligand) into the oxy-hydroxyl-Co species after electron transfer. The textural and electrochemical characteristics of resultant Co oxides, examined by X-ray photoelectron spectroscopic (XPS), scanning electron microscopic (SEM), open-circuit potential versus time, and cyclic voltammetric analyses, are also influenced by varying the complex agents. The deposition rate is the highest when the Co oxide is deposited from the precursor solution containing AcO−, which also exhibits the highest specific capacitance of ca. 230 F g−1 among all Co oxide deposits (as the oxide loading ≥0.05 mg cm−2), demonstrating its most promising applicability in the electrochemical supercapacitors.