Study of the electrochemical deposition and properties of cobalt oxide species in citrate alkaline solutions

Glassy carbon electrode substrates coated with thin films of cobalt oxyhydroxide were investigated in moderately alkaline medium by cyclic voltammetry. The cobalt oxide formation process was accomplished in alkaline solution (30 mM NaOH) containing millimolar concentrations of CoCl₂ and ligand species such as sodium citrate. The cobalt oxide/hydroxide films were obtained either by voltage cycling between 0.4 and 1.1 V versus SCE or under potentiostatic conditions at moderate positive potentials (i.e. 0.5 V). The resulting electrodeposited film was characterized electrochemically in alkaline solutions by cyclic voltammetry and, independently of the electrodeposition procedure adopted, reveals three well-defined sets of redox waves related to the Co(OH)₂/Co₂O₃, Co₂O₃/CoOOH and CoOOH/CoO₂ electrochemical transitions. The charge/discharge processes and the oxygen evolution reaction during continuous potential cycling were severely inhibited in the presence of increasing concentrations of electroinactive electrolytes (i.e. NaNO₃, K₂SO₄, Na₃PO₄, etc.). The electrochemical behaviour of the electrodeposited cobalt oxide/hydroxide film in alkaline solution and in the presence of various organic molecules was also investigated.