Carbon addition to electrodeposited Co-Mo alloys was made to enhance electrolytic hydrogen evolution activity and to prevent open-circuit corrosion in 8 M NaOH at 90degreesC. Co-30 atom % Mo alloy showed the highest activity for hydrogen evolution among the binary Co-Mo alloys, but open-circuit immersion resulted in dissolution of molybdenum as molybdate, with a consequent decrease in the hydrogen evolution activity. Addition of carbon to electrodeposited Co-Mo alloys by adding lysine in the deposition electrolytes further enhanced hydrogen evolution activity and slowed dissolution of molybdenum during open-circuit immersion, although complete prevention of dissolution of molybdenum was not attained. (C) 2003 The Electrochemical Society.