Abstract
The Tafel responses [i.e., log(i)-E] of the anodic deposition for hydrous manganese oxide (denoted as MnO x ·nH 2 O) from MnCl 2 ·4H 2 O with the presence of acetate ions (CH 3 COO - , AcO - ) are systematically examined. Variables studied in this work include the concentration of Mn 2+ and AcO - as well as the temperature and pH of the plating solution. The decrease in the Tafel slope for this anodic deposition, defined as (1-α)F/23RT, indicates that 1-α is monotonously increased from 0.18 to 0.4 with increasing the concentration of AcO - . The average reaction orders of AcO - and Mn 2+ are about 2/3 and 1/3, respectively. The pseudo-equilibrium potential of the anodic deposition of MnO x ·nH 2 O, obtained from the log(i)-E responses, is linearly decreased with increasing pH of the plating solution (slope = 117.8 mV/decade). The onset potential for the anodic deposition of MnO x ·nH 2 O, examined by linear sweep voltammetry (LSV), is negatively shifted with the continuous addition of acetate ions into the MnCl 2 ·4H 2 O solution. This reduction in the deposition potential is attributed to the formation of Mn-AcO complexes [presumably denoted as Mn(AcO)δ(H 2 O) 6-δ (2-δ)+ ], revealed by the electron paramagnetic resonance (EPR) analyses and the molecular orbital/ligand field stabilization energy theory. The influence of deposition potentials on the mean oxidation state of MnO x ·nH 2 O is also investigated by the EPR analyses. Finally, a scheme corresponding to the anodic deposition of MnO x ·nH 2 O from MnCl 2 ·4H 2 O with the presence of AcO - is proposed. © 2005 The Electrochemical Society. All rights reserved.