Deposition of β-Co(OH)₂ Films by Electrochemical Reduction of Tris(ethylenediamine)cobalt(III) in Alkaline Solution

Abstract

Films of β-Co(OH)2 with a dense microcone morphology are electrodeposited at room temperature by reducing tris(ethylenediamine)cobalt(III) in alkaline solution. The synthesis exploits the fact that the kinetically inert Co(III) complex of ethylenediamine (en) is 35 orders of magnitude more stable than the kinetically labile Co(II) complex. [Co(en)3]3+ is therefore stable in alkaline solution, but [Co(en)3]2+ reacts with excess hydroxide ion to produce β-Co(OH)2. The electrodeposited β-Co(OH)2 is an active catalyst for the oxygen evolution reaction. Raman spectroscopy suggests that the surface of β-Co(OH)2 is converted to CoOOH at the potentials at which oxygen evolution occurs.