Effect of phosphoric acid on the performance of Pb-1.7%Sb grid of lead-acid cell is studied in 5 M H 2 SO 4 by cyclic galvanostatic polarization and impedance spectroscopy. An increase in capacitance to a maximum is recorded during the initial stages of the electro-reduction of PbO 2 into Pb(II) compounds and attributed to concurrent compositional and dimensional changes. These changes include removal of O 2 bubbles, insertion of large amounts of H 2 SO 4 and H 2 O. Efficiency of PbO 2 formation decreases, while its rate of self-discharge increases with increasing the charging current and in the presence of H 3 PO 4 . The charge capacity increases with increasing the discharging current due to the decrease in the self-discharge. The charge capacity is lower in the presence of H 3 PO 4 . On increasing the cycle number, the corrodibility of the grid increases, because more layers of the surface Pb are involved in the self-discharge. H 3 PO 4 significantly retards the effect of cycle number.
Potentiostatic oxidation of Pb-1.7%Sb alloy used in the manufacture of grids of lead-acid batteries over the potential range from −1.0 V to 2.3 V in 5 M H 2 SO 4 in the absence and the presence of 0.4 M H 3 PO 4 and the self-discharge characteristics of the oxide layer formed is studied by electrochemical impedance spectroscopy (EIS). Depending on the potential value, sharp variations in resistance and capacitance of the alloy are recorded during the oxidation and they can be used for identification of the various substances involved in passive layer. Addition of H 3 PO 4 is found to deteriorate the insulating properties of the passive layer by the retardation of the formation of PbSO 4. H 3 PO 4 completely inhibits the current and impedance fluctuations recorded in H 3 PO 4-free solutions in the potential range 0.5 V-1.7 V. These fluctuations are attributed to the occurrence of competitive redox processes that involve the formation of PbSO 4 , PbOSO 4 , PbO and PbO 2 and the repeated formation and breakdown of the passive layer. Self-discharge experiments indicate that the amount of PbO 2 formed in the presence of H 3 PO 4 is lesser than in the H 3 PO 4-free solutions. The start of transformation of PbSO 4 into PbO 2 is greatly shortened. H 3 PO 4 facilitates the diffusion process of soluble species through the passive layer (PbSO 4 and basic PbSO 4) but impedes the diffusion process through PbO 2 .
:Potentiostatic oxidation of Pb-1.7%Sb alloy used in the manufacture of grids of lead-acid batteries over the potential range from −1.0 V to 2.3 V in 5 M H 2 SO 4 in the absence and the presence of 0.4 M H 3 PO 4 and the self-discharge characteristics of the oxide layer formed is studied by electrochemical impedance spectroscopy (EIS). Depending on the potential value, sharp variations in resistance and capacitance of the alloy are recorded during the oxidation and they can be used for identification of the various substances involved in passive layer. Addition of H 3 PO 4 is found to deteriorate the insulating properties of the passive layer by the retardation of the formation of PbSO 4 . H 3 PO 4 completely inhibits the current and impedance fluctuations recorded in H 3 PO 4 -free solutions in the potential range 0.5 V-1.7 V. These fluctuations are attributed to the occurrence of competitive redox processes that involve the formation of PbSO 4 , PbOSO 4 , PbO and PbO 2 and the repeated formation and breakdown of the passive layer. Self-discharge experiments indicate that the amount of PbO 2 formed in the presence of H 3 PO 4 is lesser than in the H 3 PO 4 -free solutions. The start of transformation of PbSO 4 into PbO 2 is greatly shortened. H 3 PO 4 facilitates the diffusion process of soluble species through the passive layer (PbSO 4 and basic PbSO 4 ) but impedes the diffusion process through PbO 2 .
The electrochemical performance of positive pole grids of lead-acid batteries made of Pb-0.08%Ca-1.1%Sn alloys without and with 0.1 wt% of each of Cu, As or Sb and with 0.1 wt% of Cu, As and Sb combined was investigated by electrochemical methods in 4.0 M H 2 SO 4. The corrodibility of alloys under open-circuit conditions and constant current charging of the positive pole, the positive pole gassing and the self-discharge of the charged positive pole were studied. All impurities (Cu, As, Sb) were found to decrease the corrosion resistance, R corr after 1/2 hour corrosion, but after 24 hours an improvement in R corr was recorded for Sb containing alloy and the alloy with the three impurities combined. While an individual impurity was found to enhance oxygen evolution reaction, the impurities combined significantly inhibition this reaction and the related water loss problem was improved. Impedance results were found helpful in identification of the species involved in the charging/discharging and the self-discharge of the positive pole. Impurities individually or combined were found to increase the self-discharge during polarization (33-68%), where Sb containing alloy was the worst and impurities combined alloy was the least. The corrosion of the positive pole grid in the constant current charging was found to increase in the presence of impurities by 5-10%. Under open-circuit, the self-discharge of the charged positive grids was found to increase significantly (92-212%) in the presence of impurities, with Sb-containing alloy was the worst. The important result of the study is that the harmful effect of the studied impurities combined was not additive but sometimes lesser than any individual impurity.
:The electrochemical performance of positive pole grids of lead-acid batteries made of Pb-0.08%Ca-1.1%Sn alloys without and with 0.1 wt% of each of Cu, As or Sb and with 0.1 wt% of Cu, As and Sb combined was investigated by electrochemical methods in 4.0 M H 2 SO 4 . The corrodibility of alloys under open-circuit conditions and constant current charging of the positive pole, the positive pole gassing and the self-discharge of the charged positive pole were studied. All impurities (Cu, As, Sb) were found to decrease the corrosion resistance, R corr after 1/2 hour corrosion, but after 24 hours an improvement in R corr was recorded for Sb containing alloy and the alloy with the three impurities combined. While an individual impurity was found to enhance oxygen evolution reaction, the impurities combined significantly inhibition this reaction and the related water loss problem was improved. Impedance results were found helpful in identification of the species involved in the charging/discharging and the self-discharge of the positive pole. Impurities individually or combined were found to increase the self-discharge during polarization (33-68%), where Sb containing alloy was the worst and impurities combined alloy was the least. The corrosion of the positive pole grid in the constant current charging was found to increase in the presence of impurities by 5-10%. Under open-circuit, the self-discharge of the charged positive grids was found to increase significantly (92-212%) in the presence of impurities, with Sb-containing alloy was the worst. The important result of the study is that the harmful effect of the studied impurities combined was not additive but sometimes lesser than any individual impurity.
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