In spite of the many studies performed since the beginning of the last century, the Fe electrode, used as negative of both Ni/Fe and Fe/Air batteries, still poses several problems. For instance, according to the current literature, the following points are still not clear: (i) whether and how the depth of discharge affects electrode performance; (ii) what pathway the discharge follows, generally assumed as it is to involve consecutive Fe → FeII and FeII → FeIII oxidation; (iii) why, at room temperature, only a minor fraction of the large theoretical capacity can be exploited. The present paper shows that deep discharges do increase Fe electrode performance, since they induce a transitory inhibition of hydrogen evolution. Likewise, Fe/Metal oxide composite electrodes have shown that the formation of FeIII in discharge can take place directly from Fe, when the discharging rate applied is no longer compatible with the increase in electrode resistance due to oxidation products. Fe/Intermetallic compound composite electrodes have been studied as possible routes for increasing the efficiency of Fe capacity: useful indications have been gained as regards the compatibility of Fe with an IMC for charge storage.
