Mass changes accompanying the electrochemical reaction of sol-gel formed 50 : 50 Ni-Co oxide films

Cyclic voltammetry (CV) and the electrochemical quartz crystal microbalance (EQCM) technique have been employed to monitor the mass changes during pot ential cycling of sol-gel (SG) formed 50:50 Ni-Co oxide films in 0.5 M NaOH solutions. The experimentally determined pH dependence, together with the EQCM measurements, have confirmed that charging and discharging of SG Ni-Co oxide films is accompanied by the injection/expulsion of mobile ions, sugg ested to be OH- and Na+. Although an unambiguous identification of the spec ies involved in the mass transport within the oxide films cannot be made by CV and EQCM alone, these studies provide a deeper insight into morphologic al changes of the SG oxide films which occur with time of cycling in alkali ne solutions. A model involving water exchange during the redox process of these films is proposed, with water being expelled during oxidation and inj ected upon reduction. An increased amount of exchanged water with longer cy cling times may indicate the early stages of the degradation of SC-formed 5 0:50 Ni-Co oxide films. (C) 2000 Elsevier Science B.V. All rights reserved.