Mercuric oxide reference electrodes

In battery practice, hydrogen reference electrodes are not used. They are not only difficult to handle, but include in addition the risk of contamination of the battery s electrodes by noble metals like platinum or palladium (4). Instead, a number of reference electrodes are used, e.g. the mercury/mercurous sulfate reference electrode (Hg/Hg2S04) in lead-acid batteries, and the mercury/mercuric oxide reference electrode (Hg/HgO) in alkaline solutions (e.g. Ref. 5). In lithium ion batteries with organic electrolyte the electrode potential is mostly referred to that of the lithium electrode (cf. Chapter 18). 

Fig. 7. Continuous recording of the limiting current Oxidation of fAreo-l,2-diphc-nylethyleneglycol by periodate. Decrease in the periodic acid concentration with time. 1M Acetate buffer of pH 4.3, 5 x 10 5 M-KIO4, 5 x 10 8Af diol. Current recorded at 10.4 V (mercurous sulphate reference electrode) at 15° C. Figures on the abscissae give the time in minutes the galvanometer zero and the current before the addition of periodate and after addition at / = 0 are marked. Full scale sensitivity 0.8 [zA...

Fig. 10. Oxidation of fAteo-l-phenylpropane-l,2-diol by periodate. 1M acetate buffer pH 4.7. 1 X 10 5 periodate, 1 x 10diol, 25° C. Time (in minutes) after which the recording of each curve was started is noted. Curves starting at 0 V, 200 mV/absc., 450 mV/min., mercurous sulphate reference electrode, h = 50 cm, full scale sensitivity 0.6 [ A...

To simulate corrosion in lead-acid battery environments, Dacres et al. [118] and others [119,120] anoically polarized test materials at 1.226 V (versus mercury/mercurous sulfate reference electrode) in sulfuric acid solutions (of 1.285 specific gravity) at 50, 60, and/or 70°C. At 1.226 V, lead and water are oxidized to lead dioxide (Pb02) and molecular oxygen (O2), respectively [122,123]. About one third of the total anodic current is consumed in the oxidation of lead under these conditions [120]. 

In selecting reference electrodes for practical use, one should apply two criteria that of reducing the diffusion potentials and that of a lack of interference of RE components with the system being studied. Thus, mercury-containing REs (calomel or mercury-mercuric oxide) are inappropriate for measurements in conjunction with platinum electrodes, since the mercury ions readily poison platinum surfaces. Calomel REs are also inappropriate for systems sensitive to chloride ions. 

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