Studies on pressed and roll-compacted alkaline iron-electrodes for nickel-iron secondary cells

Abstract

It is concluded that various sulfide additives employed in this study retard passivation of the iron electrode during discharge and suppress the rate of the HER during charging. The electrodes doped with Bi?S? show minimum passivation and maximum suppression of the HER. Accordingly, the electrodes doped with Bi?S? exhibit best performance among the various electrodes investigated. This study demonstrates that by measuring steady?state, open?circuit potentials of alkaline?porous?iron electrodes as a function of its state?of?charge values, it is possible to determine the class of mechanisms involved during its discharge steps. It is inferred that, while the first discharge?step is heterogeneous type, the second discharge?step involves homogeneous solid?state oxidation of Fe(OH)? to ??FeOOH. As the measurements have been made under equilibrium conditions, the conclusions are more reliable than those from polarisation studies. The present study suggests that it is possible to prepare mechanically rugged and electrochemically stable porous?iron electrodes with Teflon suspension. The presence of nickel oxide and Bi?S? in these electrodes helps reduce the ohmic resistance and passivation of the iron?active material. The performance of such iron electrodes is encouraging for their commercial exploitation.