The elementary physicochemical processes during the first stage of formation of the negative lead-acid battery plate

During the first formation stage of the negative plate in H₂SO₄ solution lead monoxide and tribasic sulphate transform into Pb and PbSO₄ giving rise to a Pb?PbSO₄ zone. It was established that these processes take place within a thin layer (the δ-layer) situated between the Pb?PbSO₄ zone and the paste. The rate determining step is the transport (by diffusion and migration) of H⁺ and SO₄^2? ions from the bulk of the electrolyte towards the δ-layer. An equation is derived for the dependence of the concentration of the H₂SO₄ in the Pb?PbSO₄ zone on the thickness of this zone. It was found that during formation until a limiting thickness of the Pb?PbSO₄ zone, PbSO₄ originates mainly at the expense of the H₂SO₄ present in the bulk of the electrolyte. When the formation rate of PbSO₄ becomes very small the reaction of PbSO₄ reduction to Pb takes place. This reaction proceeds in a second reaction layer (the α-layer) which is located in the Pb?PbSO₄ zone at the plate surface. Subsequently, the formation of PbSO₄ in the δ-layer takes place at the expense of H₂SO₄ generated in the α-layer. The model is confirmed by the experimentally determined distribution of PbSO₄ across the cross-section of the plate during formation.