Oxygen Evolution Overpotential of Pb-based Insoluble Anode Containing Ru Oxide Powders Prepared by Liquid-phase Reaction and Heating

Abstract

limit. Thus, it becomes very important to reduce the anode overpotential η a in order to reduce the bath voltage. In addition, a significant part of the anode overpotential is the oxygen evolution overpotential. Therefore, it can be concluded that an effective way to reduce the electric power required for Zn electrowinning is to reduce the oxygen evolution overpotential on the Pb-based insoluble anode 4) . Our research team has produced a Pb-based anode containing homogeneously distributed oxide powders as the electrode catalyst by adopting a new powder-rolling method 5,6) , which replaces the conventional cast-rolling method 7-9) . Pb- based anodes containing various oxide catalysts have been produced by this powder-rolling method and the anode potential investigated by galvanostatic electrolysis. A remarkable decrease in anode potential was observed in a Pb-based powder rolled anode containing RuO 2 powder as the electrode catalyst (See Figure 1). It was concluded that the alternative Pb-based anode incorporating RuO 2 powder was very effective in decreasing the oxygen evolution overpotential and reducing the electric power required for Zn electrowinning . Ruthenium oxide powders were produced by the reaction of an RuCl 3 solution with H 2 O 2 , followed by heating of the resulting precursor at a temperature between 200°C and 600°C in air. Pb-based anodes containing these heated products of 1.0 mass% were prepared by the powder-rolling method, and the effect of the heated product as an electrode catalyst on lowering the anode potential was investigated in order to develop an energy-saving insoluble anode for Zn electrowinning. Based on XPS results, RuO 2 with a signi fi cant amount of RuO 2 ･ n H 2 O was produced by heating the precursor at 250°C or lower. The ratio of RuO 2 to RuO 2 ･ n H 2 O increased remarkably above 300 ° C and the potential of the Pb-based anode decreased in inverse proportion to the RuO 2 content of the heated product. The lowest anode potential of 1.72 V vs. NHE, which was about 360 mV lower than that of the anode with the unheated precursor, was observed for the Pb-based anode containing the product heated at 400°C. However, the anode potential of the Pb-based anode increased again when the heating temperature was 500°C or higher. The subsequent increase in the anode potential was probably caused by a decrease in the active sites of the oxygen evolution reaction, that is, the grain growth of the heated product decreased the effective reaction area of the RuO 2 catalyst.