Incorporating an Efficient Oxygen Evolution Catalyst of MnCo2O4.5 into a Pb Matrix as an Energy-Saving Anode for Metal Electrowinning

Abstract

Based on the outstanding catalytic activity and stability of Mn-Co bimetallic oxides toward oxygen evolution in acidic solutions, MnCo2O4.5 was incorporated into a Pb matrix through a powder pressing-sintering process to obtain a Pb-MnCo2O4.5 composite anode. The results show that compared with the Pb anode that was made via the powder pressing-sintering process (PS-Pb), the oxide layer formed on the Pb-MnCo2O4.5 anode presented a higher flatness, compactness, and β-PbO2 concentration. Consequently, Pb-5.0MnCo2O4.5 presented a stable anodic potential of 1.235 V, approximately 170 mV lower than that of the PS-Pb anode. In the case of lower MnCo2O4.5 content (≤2.5%), the Pb-MnCo2O4.5 composite anode exhibited a smaller Tafel slope (70.39 ∼ 79.59 mV dec−1) and a lower charge transfer resistance (0.437 ∼ 0.676 Ω cm2). The fresh Pb-5.0MnCo2O4.5 composite anode showed a self-corrosion density of 0.25 mA cm−2, approximately 14.3% of that tested on the PS-Pb anode. However, Co2+ and Mn2+ were detected in the electrolyte during 72 h of electrowinning with the Pb-MnCo2O4.5 composite anode. In summary, the Pb-MnCo2O4.5 composite anode has the potential to reduce the energy consumption of the metal-electrowinning process. Nonetheless, it is necessary to evaluate the influence of dissolved Co2+ and Mn2+ on the cathodic process before commercial application.