Effect of pH Value on Structure and Properties of Anodic Electrodeposited Mn-Mo Oxide

By correction to the thermodynamic calculation based on E0-pH diagram of MnSO4-SO42--H2O plating system, effective pH value range for anodic electrodeposition of MnO2 phase structure materials got clear, at 363K, with Mn2+ concentration 0.2mol·dm-3. The influence law of the pH values was also obtained based on the characterization of the oxide structure and test of its electrochemical performance. The results show that pH value in the 0.33-3.4 range, with its increase and accordingly the conducive to the effective deposition of MnO2 type Mn-Mo oxide. However, although with pH value increasing, deposition efficiency improves, the coating quality gets degraded, especially making the electrocatalytic performance of the oxide obviously deteriorated. It also shows that with pH value of plating solution 0.5, obtained Mn-Mo oxide has excellent coating quality and high electrocatalytic activity. The reason is closely related to competition in oxygen evolution reaction during the preparation of the oxide. When pH value is small, oxygen evolution reaction competition causes the solid-liquid interface stirring, the dendritic growth of oxide gets inhabited and the diffusion layer gets thinning, which promotes the nucleation of oxide on the electrode micro-surface and makes grain refined, so as to improves the electrocatalytic performance of oxide.