Abstract
In this work, the electrochemical behavior and the corresponding mass variation of amorphous manganese oxide (denoted as a-MnO x ) are examined simultaneously in a neutral electrolyte containing 10 mM Na 2 SO 4 without or with NaHCO 3 or Na 2 HPO 4 by cyclic voltammetry with a quartz crystal microbalance (QCM). a-MnO x was anodically deposited onto the gold-sputtered quartz electrode by means of a potentiostatic method at 1.0 V for 60 s. The morphology and microstructure of a-MnO x with different potential windows of CV cycling in the above electrolyte were examined by means of the scanning electron microscopy (SEM). From this EQCM study, a-MnO x is unstable between 1.0 and 1.2 V in 10 mM Na 2 SO 4 because of significant dissolution of a-MnO x . The repeated potential cycling promotes the electrocatalytic activity of a-MnO x for oxygen evolution, which also enhances the dissolution of a-MnO x . The dissolution phenomenon and oxygen evolution are successfully suppressed by the formation of insoluble manganese carbonate or the adsorption of phosphate by adding NaHCO 3 or Na 2 HPO 4 in the Na 2 SO 4 electrolyte, enlarging the potential window for the charge/discharge of a-MnO x . © 2011 Elsevier Ltd.