Electrochemical investigations on composite iron electrodes

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 → Fe^II and Fe^II → Fe^III 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 Fe^III 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.