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

摘要

Ruthenium oxide powders were produced by the reaction of an RuCl_3 solution with H_2O_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 significant amount of RuO_2 · nH_2O was produced by heating the precursor at 250°C or lower. The ratio of RuO_2 to RuO_2-nH_2O 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.