Rapid growth and improved functions of mobile equipment present the need for an advanced rechargeable battery with extremely high capacity. In this study, we investigated the application of fuel cell technology to an Fe-air rechargeable battery. Because the redox potential of Fe is similar to that of H(2), the combination of H(2) formation by the oxidation of Fe with a fuel cell has led to a new type of metal-air rechargeable battery. By decreasing the operating temperature, a deep oxidation state of Fe can be achieved, resulting in enlarged capacity of the Fe-air battery. We found that the metal Fe is oxidized to Fe(3)O(4) by using H(2)/H(2)O as mediator. The observed discharge capacity is 817 mA h g(-1)-Fe, which is approximately 68% of the theoretical capacity of the formation of Fe(3)O(4), 1200 mA h g(-1)-Fe, at 10 mA cm(-2) and 873 K. Moreover, the cycle stability of this cell is examined. At 1073 K, the cell shows a discharge capacity of ca. 800 mA h g(-1)-Fe with reasonably high discharge capacity sustained over five cycles.