Organic expander action at lead electrodes
thesisposted on 29.11.2010 by Phillip J. Mitchell
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The instrumentation for digitally driven electrochemical experiments has been developed. Software has been written for experimental control and high speed data aquisition. The digital control methods were successfully used in the study of the electrochemistry of the porous lead electrode (the lead-acid battery negative plate), over an extended temperature range. The effects of a number of commercially pertenent additives have been studied at reduced temperatures. These reaction enhancing materials (expanders) have been studied in detail on both planar and porous lead electrode in sulphuric acid in the range 1M to 5M. Deductions concerning the energetics of the reactions have been made from experimental results. The modes of action of certain expanders are discussed. It was concluded that on the plane lead surface solution phase expander materials modify the mechanism of the lead sulphate electrocrystallisation - the current limiting reaction. This was an effect on the solid state process although a solution Pb2+ process was identified (for the first time) in battery strength acid. Electrode incorporated organic expander materials act by modifying pore geometies and reaction penetration depths. The current transients due to electrocrystallization in porous lead are very complex and require very sophisticated modelling techniques to provide a useful fit.