Redox coupled ion exchange in cobalt oxide films

Ion exchange coupled to oxidation-reduction cycling of electrochromic cobal t oxide films was studied using Probe Beam Deflection (PBD) techniques. The films were deposited by potentiodynamic cycling of glassy carbon electrode s in aqueous Co+2 solution. The cyclic voltammograms of cobalt oxide films present three peaks in basic (pH = 13) solution. The PBD signal is positive during oxidation indicating insertion of hydroxide ions. The results are c onfirmed by monitoring the PBD signal during pulse potential experiments at varying distances of the beam from the electrode. Using the theory of PBD behaviour for discontinuous reactions, a diffusion coefficient for the mobi le ion of 1.68 x 10(-5) cm(2)/s was measured, which agreed with that observ ed for NaOH diffusion in similar systems. The results are explained on the basis of a scheme of solid state oxidations from Co-II to Co-IV in three re dox steps, coupled to hydroxide ion insertion. (C) 2001 Elsevier Science B. V. All rights reserved.