Journal of Power Sources, 30 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGF (1990) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM 161 - 167 161 FILM FORMATION IN THE Pb(I1) REGION OF THE Pb/H,SO, SYSTEM L. A. AVACA’, E. R. GONZALEZ and G. TREMILIOSI-FILHO Grupo a!e Ektroquimica, IFQSCIUSP, C.P. 36913560 Sdo Carlos (SP) (Brazil) C. V. D’ALKAINE Grupo de Ektroquimica, DQ-UFSCar, C.P. 676-13660 S&I Carlos (SP) (Brazil) Introduction A detailed knowledge of the initial stages of formation and reduction of the different films on lead is essential for the complete understanding of the complex processes involved in a working cycle of a lead/acid battery. In particular, the rationalization of the processes occurring after the PbSO, formation, but before PbO, generation, requires a clear description of the sulphate layer formation/reduction mechanism under the same experimental conditions. This may help to clarify some of the controversies existing in the literature with regard to the models used for the description of the Pb(I1) region [ 1 - 31. This work explores, in detail, the voltammetric characteristics of lead in 5 M H,SO, solutions. Special attention is given to the charges involved in each process, in order to make better use of the electrochemical technique. On this basis, the analysis is focussed on the anodic extreme of the Pb(II) potential region where different films co-exist during the voltammetric exper- iments. Experimental Working electrodes comprised lead rod (Aldrich Gold Label 99.9995%) with a diameter of 0.4 cm that was glued inside a Pyrex glass tube with epoxy resin (slow cure). The resulting exposed area was 0.13 cm’. The surface was mechanically polished with 600 grade emery paper using water as both a lubricant and a cooling agent. The electrode was then treated with a saturated solution of ammonium acetate, washed, and immediately intro- duced into the cell. The electrode was polarized at - 1.2 V uers’sus an Hg/ Hg,S0,/5 M H,SO, reference electrode, to which all potentials in this work are referred. Unless otherwise stated, each voltammogram was conducted on ‘Author to whom correspondence should be addressed. 03787753/90/$3.50 0 Elsevier Sequoia/Printed in The Netherlands