The electrochemical characteristics of binary manganese-cobalt oxides prepared by anodic deposition

Hydrous manganese-cobalt oxides (denoted as (Mn + Co)O-x.nH(2)O) were anodically deposited onto graphite substrates from 0.01 M MnCl2 + 0.09 M CoCl2 solutions with various pH values. The electrochemical characteristics of these oxide deposits were examined by cyclic voltammetry (CV) in 0.1 M Na2SO4 with changing pH values. The voltammetric behavior of (Mn+Co)O-x-nH(2)O was not significantly influenced by changing the pH value of Na2SO4 from 4 to 10. The surface morphology and composition of (Mn+Co)O-x.nH(2)O deposits were obtained from scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), respectively, which were affected by changing the pH values of deposition solutions. The number of cracks on the deposit surface was found to increase with the Co content in the Mn oxide matrixes. When deposits were subjected to anodic polarization at potentials positive than 1.2 V, these binary (Mn + Co)O-x.nH(2)O exhibited capacitive-like behavior with specific capacitance approximately equal to 125 F g(-1) (measured at 25 mV s(-1)) for supercapacitors. (c) 2005 Elsevier B.V. All rights reserved.