The Discharge Mechanism of Certain Oxide Electrodes

Abstract

The discharges of PbO~, TiO~, and TLOz electrodes were studied and are compared with similar discharges of the MnO~ electrode. The overpotentials of PbO~ and TiO2 electrodes at small current densities are linear functions of the current density, but TLO~ is like MnO~ in having a square-root relation. It is considered that the first step in the electrode reaction is reduction to a lower oxide or hydroxide and that the subsequent disposal of this is rate-determining. The square-root relation is correlated with the existence of an unstable valence state between the initial and final products. A few experiments with Ce(OH), and SnO~ electrodes were carried out, but these were less satisfactory as current-producing electrodes than the others.

The Recovery from Polarization of a- and β-PbO[sub 2] in H[sub 2]SO[sub 4] Electrolyte

“…These experimental observations are consistent with the previously proposed theory that the crystal lattice of fl-PbO2 undergoes a considerable expansion as the lower oxide reduction product is formed on and within the electrode surface, but the a-PbO2 lattice does not undergo appreciable expansion (4,5). As the fl-PbO2 electrode recovers from polarization, the lower oxide is removed from the surface and from within the electrode lattice, which raises the potential of the system.…”

“…This potential maximum was also observed in each recovery of an electrode from a series of successive polarizations. This maximum was not observed previously (4,5). The potential-time curve for the recovery of a-PbO2 from polarization did not, however, exhibit a potential maximum under any condition.…”

“…The potential-time curves obtained when the two crystallographic modifications of PbOe" (1, 2), ~-PbO2(rhombic) and the more common fl-PbO2 (tetragonal), recover from polarization in acid electrolyte have been re-examined using more sensitive recording conditions (3) than employed in previously reported work (4,5). Cylindrical platinum electrodes (surface area equal approximately 5 cm2), plated with either a-or fl-PbO2, were discharged by passing a constant cathodic current until a steady-state or slowly changing closed circuit potential was obtained.…”

“…The electrodes were in contact with a stirred 0.1M HeSO4 electrolyte saturated with PbSO4. Details of the experimental conditions, apparatus, and procedure were identical to those described previously (3)(4)(5).…”

“…The fact that ~-PbO2 does not exhibit a potential minimum on discharge (4,5) leads to the postulation that a-PbOe does not undergo a similar lattice expansion.…”