The use of Hg/Hg2SO4 reference electrodes in valve-regulated lead/acid cells

Reference electrode and gas flow measurements were used to characterize the discharge and charge behavior of a valve-regulated lead/acid cell. The implementation of a Hg/Hg2SO4 reference electrode suitable for this type of cell is described. The nature of the reference electrode gives rise to liquid junction potentials. The liquid junction potential theory is reviewed and applied to correct the measured half-cell potentials during cell operation. Corrections of over 60 mV were required for measurements at the end of discharge and beginning of charge. The PbO2 electrode is shown to control the decrease in cell voltage during discharge; that is, discharge capacity is limited by the PbO2 electrode. In contrast, during galvanostatic charge to a charge-voltage lid, the final cell voltage increase is controlled by the Pb electrode.