Hydrogen content and lead vacancies in β-PbO2 from active battery plates

Abstract

Numerous chemical analyses of lead dioxide, PbO/sub 2/, have shown it to be a nonstoichiometric compound with a deficiency of active oxygen and sufficient adsorbed or lattice water or hydroxl ions to give an overall Pb:0 ratio near 1:2. The oxygen deficiency and the amount of hydrogen (assumed to be in the form of H/sub 2/O or OH) was found to depend on the method of preparation. For the neutron diffraction studies reported in this paper two 10 gm samples of ..beta..-PbO/sub 2/ were obtained from cycled commercial lead-acid battery plates. One cell contained H/sub 2/SO/sub 4/ electrolyte while the other contained D/sub 2/SO/sub 4/ electrolyte. The diffraction data were obtained on the back scattering detectors (20 = +/- 160/sup 0/) of the high resolution powder diffractometer at Argonne's ZING-P' pulsed neutron source. From these results it is clear that there are not large numbers of oxygen vacancies in electrochemically formed ..beta..-PbO/sub 2/ as had been previously suggested. If hydrogen is incorporated as lattice water or hydroxl ions the oxygens of these species occupy regular oxygen sites. The observed existence of 3-5% lead vacancies suggests that charge balance may be achieved by incorporation of H in the ..beta..-PbO/sub 2/ lattice.more » Within experimental uncertainties, the 0.21 H atoms per PbO/sub 2/ unit observed in the bulk sample is in general quantitative agreement with the refined lead (Pb/sup 4 +/) vacancy concentration. Unfortunately, the present results do not rule out the possible existence of an amorphous component or poorly crystallized surface layers.« less