Electrochemical reduction and hydrogenation of Co oxides

The electrochemical hydrogenation properties of CoO and Co3 O4 powders were investigated and compared to those of hexagonal close-packed Co. The discharge capacity was measured in KOH aqueous solution under a controlled current density 500 mAg. The maximum reversible discharge capacities of Co, CoO, and Co3 O4 were 415 mAhg (2 h charging), 389 mAhg (2 h charging), and 426 mAhg (5 h charging), equivalent to CoH0.91, CoH0.85, and CoH0.93, respectively. Because CoO and Co3 O4 are mostly reduced to Co in the initial charge stage, the discharge capacities of both oxides are mainly from dehydrogenation of CoHx.