Electrochemical quartz crystal microbalance probing the electro-formed andelectro-reduced products on a copper electrode in aqueous solutions containing NaHCO3 and Na2CO3

The electrochemical behaviors of a copper electrode in alkaline solutions c ontaining NaHCO3 and Na2CO3 have been in-situ studied by using an electroch emical quartz crystal microbalance (EQCM) combined with cyclic voltammetry (CV) technique. Through the voltammetry and mass curves recorded simultaneo usly, the effective equivalent molar mass (EMM) as a function of the potent ial was obtained and applied to identification of the reaction species of t he electro-formed and electro-induced layers. As for a copper in 0.05 M NaH CO3 + 0.05 M Na2CO3 solution, the electrode reaction mechanisms were propos ed on the basis of the analysis of EQCM data. The results indicated that th e initial formations of the anodic layer involve an inner Cu2O layer, follo wed by a middle CuO-Cu(OH)(2) layer, and finally a complex outer [Cu(OH)(2) . CuCO3] layer with two possible formula. It was detected that the formatio n of soluble Cu(TI) species in the anodic scan and the re-formed precipitat ion of these soluble species in the cathodic scan, accompanying a decrease and an increase of the electrode mass, respectively. The latter was found t o be effectively hindered by the two cathodic reduction reactions. The diff erence of EQCM responses From a copper in solutions containing different Na HCO3-Na2CO3 concentration ratios was discussed according to the electrode r eaction mechanisms proposed. (C) 2000 Elsevier Science Ltd. All rights rese rved.