Studies on porous iron electrodes for alkaline storage batteries and supplementary investigation on porous lead electrodes of lead-acid

Abstract

It has been demonstrated that an analysis of the open-circuit transients is useful for understanding several aspects of the alkaline iron electrodes. It provides diagnostic criteria for studying the effect of additives. The self-discharge kinetics of alkaline iron electrode has also been studied with and without the sulphide additive by estimating the values of corrosion currents. The variation of OCP decay patterns with SOC has also been studied. Besides, exchange current density for the parasitic HER reaction has been estimated using this phenomenology. The galvanostatic potential-time transients of porous alkaline iron electrode have been studied in the linear polarisation region to extract the kinetic parameters of both iron electrode and hydrogen electrode reactions. The effect of sulphide additive on the kinetics of both these reactions has been estimated using these kinetic parameters. The study shows that resistance variation occurring inside the pores of the electrode due to SOC variation can be significant during the operation of alkaline iron electrode. For sulphide-modified electrodes this resistance is quite small in relation to sulphide-free electrodes at high states of charge. The volume of hydrogen measured during the linear polarisation studies supplements the electrocatalytic effect of S²? ion on HER. From the above observations, it is concluded that the Pb (porous)/PbSO?, H?SO? reference electrode exhibits a stable and reproducible equilibrium potential. The electrode is also kinetically reversible and quickly recovers from any (unintended) polarisation. The electrode is easily prepared from the negative plate of commercial lead-acid batteries, and its potential is close to its thermodynamic value. The potential is independent of the SOC of the electrode although it is desirable to keep the latter within the range of about 0.85 to 0.95 for long-term stability. There is no contamination of the battery system with foreign ions with this reference electrode. The Pb(porous)/PbSO?, H?SO? (480 ?) reference electrode evolved above has been successfully employed for in-plant research and development work on lead-acid batteries at UBMEC Batteries Ltd. Operational convenience has been enhanced by immobilising the H?SO? electrolyte in the reference electrode with the addition of sodium silicate [12]. The gelled electrolyte has been found to have no significant effect on the value or stability of the equilibrium potential of the electrode.