A composite Fe2O3/C powder was applied as a negative material in iron/air batteries. The effect of charge current density on the electrochemical behavior of an electrode in KOH electrolyte without or with K2S 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 K2S additives were used, a similar phenomenon was observed, with a higher discharge capacity than that without additives. It indicated that the practical capacities of iron/air 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 Fe2O3/C electrode showed the highest discharge capacity of 810 mAh g(-1)-Fe2O3 in K2S-added electrolyte. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.049206jes] All rights reserved.