The electrochemistry of lead and porous lead electrodes has
been examined using the techniques of linear sweep voltammetry, potential
step and alternating current impedance at static and rotating disG
electrodes. Investigations were made using sulphuric acid solutions
at ambient and low temperatures. The behaviour of porous electrodes
containing additives conventionally used to improve lead-acid battery
redox processes were studied. Complementary data has been obtained
by Scanning Electron Microscopy and galvanostatic cycling experiments.
The solution reaction at the porous electrode of typical commercial
thickness, controlled by factors affecting the diffusion layer in
a direction away from the porous fsce, was found to be insignificant
in comparison with resctions occurring within the porous matrix.
The thickness of PbS04 films developed on the electrode is potentialdependent,
with thicker films st lower potentials.
The development of PbS04 on the solid lesd electrode is controlled
by nucleation and growth processes. At low overpotentials the process
is three-dimensional but becomes two-dimensional at higher overpotentials.
The behaviour of the porous electrode can be interpreted in terms of
well-established porous electrode theory, assuming the same crystallisation
processes are observed in the qaae of solid electrodes.
On reduction at both solid and· porous lead sulphate electrodes,
the electrode process has a finite depth of penetration into the
electrode. The kinetics of the formation of metallic lead from lead
sulphate on both types of electrodes appear to be by instantaneous
nucleation and two-dimensional growth, with subsequent current
limitations owing to overlap of growing lead and PbS04 depletion.
The current limitation processes are complex; the subsequent current
decay rate varies with the porosity of the electrode.
Ambient temperature investigations of the additives used in the
commercial lead electrode demonstrated that lignosulphonate facilitated
the nucleation of lead on recharge, and effected a progressive increase
in surface area/porosity of the electrode. These effects promoted
an increased utilisation of-,tbe electrode active material on discharge.
BaS04 was found to provide nucleation centres for PbS04 formation.
The low-temperature electrochemistry of solid and porous lead has
been investigated and the effects of additives are discussed.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.