Journal of Power Sources 132 (2004) 288–290 Short communication Self-discharge of Fe–Ni alkaline batteries C.A.C. Souza a , I.A. Carlos b,∗ , M. Lopes c , G.A. Finazzi b , M.R.H. de Almeida b a Departamento de Tecnologia dos Materiais, UFBA, Salvador, Brazil b Departamento de Qu´ ımica, UFSCar, C.P. 676, 13565-905, São Carlos (SP), Brazil c Departamento de Qu´ ımica, UNICENTRO, Guarapuava, Brazil Received 4 December 2003; accepted 23 December 2003 Abstract The effect of FeS and PbS on capacity and self-discharge of an iron porous electrode used in a Fe–Ni battery was investigated. Addition of 1 wt.% FeS or 1 wt.% PbS promotes a significant increase in capacity and inhibits the self-discharge of the iron electrode. This effect is most significant in the presence of PbS. © 2004 Elsevier B.V. All rights reserved. Keywords: Iron electrode; Alkaline; Batteries; Self-discharge 1. Introduction Alkaline Ni–Fe batteries present several advantages in relation to other types: longer service life, low cost and non-toxic materials, also tolerance to overcharge and deep discharge. However, the porous iron electrode has a low hy- drogen overpotential, which limits its application in com- mercial batteries [1–4]. The hydrogen evolution occurring at open circuit causes the corrosion of the iron electrode and consequently a high self-discharge rate. Furthermore, this electrode has a low charge efficiency since the hydrogen evo- lution reaction competes with the discharge reaction [5,6]. Sulfide salts, as FeS and Na 2 S are used to improve the iron electrode. Studies show that the addition of both FeS to the electrodes active material [7,8] and Na 2 S to the KOH electrolytic solution [2,9] increases significantly the iron electrode capacity. In relation to the effect of sulfide salt on the hydrogen evolution rate on the iron electrode, Bal- asubramanian and Shukla [10] measured directly the rate of hydrogen evolution under open circuit conditions in the presence and absence of FeS and PbS and observed the re- duction of the hydrogen evolution when these additives were present. These results show that this reduction is highest for PbS, in accord with the Pb hydrogen evolution potential be- ing more cathodic than Fe. However, the effect of FeS and ∗ Corresponding author. Tel.: +55-16-260-8208; fax: +55-16-260-8350. E-mail address: ivani@dq.ufscar.br (I.A. Carlos). PbS on self-discharge of the iron electrode and the effect of PbS on the electrode capacity has not been clarified yet. The aim of the present research is to investigate the effect of FeS and PbS on the Fe electrode galvanostatic discharge. 2. Experimental The iron electrodes used in this work were obtained by hot-pressing a nickel plated steel grid between two equal amounts of a mixture of electrolytic iron powder, produced in our laboratory [11], with 6% polyethylene and other addi- tives. The compacting pressure of 240 kg cm -2 was applied for 3 min maintaining the temperature at 112 ◦ C. The electrochemical measurements were carried out us- ing a three-electrode cell. The counter electrode was a nickel plate. The electrolyte was a 6 M KOH + 0.33 M LiOH so- lution. Potentials were referred to a Hg/HgO/6 M KOH ref- erence electrode. A 123 mA g -1 charge current, for 5 h, and a 12.9 mA g -1 discharge current, until the potential reached -700 mV versus Hg/HgO/6 M KOH, were applied in each charge/discharge cycle. The iron electrode self-discharge was investigated by ob- taining the electrode capacity after a time corresponding to the period in which the electrode was at rest. These mea- surements were carried out after the electrode have been submitted to stabilization cycles of charge and discharge, which are necessary for the stabilization of capacity. 0378-7753/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2003.12.043