Effect of charge current density on electrochemical performance of FeC electrodes in alkaline solutions

A composite Fe ₂O ₃C powder was applied as a negative material in ironair batteries. The effect of charge current density on the electrochemical behavior of an electrode in KOH electrolyte without or with K ₂S additives was investigated. In KOH electrolyte, the discharge capacity increased in proportion to the logarithm of charge current density in the range of 10-40 mA cm ^-2. According to an analysis of Tafel plots of the electrodes, the hydrogen evolution was found to reach its diffusion limit earlier than the reduction reaction of Fe(OH) ₂ to Fe as charge current density increased. This was deduced to be the reason for the increase of discharge capacity with current density. But as the density increased further, the discharge capacity decreased because both above reactions reached their diffusion limits. When K ₂S additives were used, a similar phenomenon was observed, with a higher discharge capacity than that without additives. It indicated that the practical capacities of ironair batteries could be increased through the depression of hydrogen evolution by optimizing the charge current density for the batteries. At a charge current density of 50 mA cm ^-2, the Fe ₂O ₃C electrode showed the highest discharge capacity of 810 mAh g ^-1-Fe ₂O ₃ in K ₂S-added electrolyte.