Capacitive and textural characteristics of manganese oxide prepared by anodic deposition: effects of manganese precursors and oxide thickness

The influence of manganese precursors on the deposition rate of hydrous manganese oxide in the amorphous form (denoted as a-MnOx.nH(2)O) and the effect of oxide thickness on the electrochemical properties of a-MnOx.nH(2)O, for application as electrochemical supercapacitors, were systematically investigated in this work. The results showed that Mn(CH3COO)(2).4H(2)O is a more promising precursor because of its high deposition rate at much lower potentials in comparison with MnSO4.5H(2)O, MnCl2.4H(2)O, and Mn(NO3)(2).4H(2)O. The capacitive characteristics of a-MnOx.nH(2)O were found to be independent of precursors, probably due to the fact that the mean oxidation state of Mn is not significantly affected by changing the anions of manganese precursors (from the XPS results). The capacity of oxide deposits was found to be proportional to the charge density of deposition (i.e., loading) of a-MnOx.nH(2)O when it was equal to or less than a critical value (ca. 3.5 C cm(-2)), while poorer capacitive behavior with a lower capacity was clearly found beyond this critical value. The a-MnOx.nH(2)O deposit with 3.5 C cm(-2), exhibiting an acceptable capacitive performance, showed the highest capacity of energy storage for supercapacitors.