A lead calcium tin alloy to which cobalt has been added is described. The alloy is useful in the formation of anodes to be used in electrowinning cells. Electrowinning cells containing the cobalt alloys are particularly suited for electrowinning metals, such as copper, from sulfuric acid electrolytes. The cobalt-containing anodes improve the efficiency of oxygen evolution at the anode during electrowinning and reduce corrosion of the anode.