A gas generating apparatus and method is described which utilizes a novel catalytic oxygen evolving electrode for such electrochemical systems as electrolysis cells and oxygen concentration cells. The electrochemical cells include a catalytic cathode and an improved catalytic anode positioned on opposite sides of, and in electrical contact with, a cation exchange membrane. A source of direct current potential between the cathode and the anode and means for removing gas from at least one of the electrodes are provided. The improved catalytic anode is a ternary platinum group reduced metal oxide alone or in combination with platinum group metals and/or platinum group metal oxides or mixtures of the foregoing having at least one valve metal component such as titanium, hafnium, zirconium, niobium, tantalum, and tungsten.