Manganese oxide electrodes with some additives enhance oxygen evolution efficiency in seawater electrolysis. Electrodes were prepared by a thermal decomposition method. IrO2-coated titanium (IrO2/Ti electrode) was used as the substrate on which manganese oxide (MnOX/IrO2/Ti) and oxide mixtures of manganese and iridium, ruthenium, platinum, iron, cobalt, nickel, tin, lanthanum, cerium or molybdenum ((Mn-M)OX/IrO2/Ti electrode, M: additives) were coated. The oxygen evolution efficiency of the MnOX/IrO2/Ti electrode was 68-70%. The addition of small amounts of nickel, cobalt, iron or tin enhanced the oxygen evolution efficiency. However the addition of excess amounts of these elements and additions of noble metals, cerium or lanthanum were detrimental for the oxygen evolution. Among the additives examined, molybdenum was the most effective additional element to increase the oxygen evolution efficiency. The addition of a small amount of molybdenum leads to a remarkable increase in the oxygen evolution efficiency up to 91%. The formation of a single phase Mn2O3 with molybdenum ions seems to be responsible for the high efficiency for oxygen evolution.
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