Additives of Suppressing Hydrogen Evolution at Carbon-Containing Negative Plates of Valve-Regulated Lead-Acid Batteries

The effects of several rare earth oxides and fluorine-containing compounds as additives on the hydrogen evolution at the negative plates containing commercial and purified carbon materials in valve-regulated lead-acid (VRLA) batteries have been studied by means of the constant current polarization and hydrogen gassing measurements. The activated carbon (AC) and iron impurity in the carbon materials greatly accelerate the hydrogen evolution. La2O3, Sm2O3, Gd2O3, Nd2O3, Dy2O3 and polytetrafluoroethlene (PTFE) as electrolyte additives inhibit the hydrogen evolution. When the hydrogen evolution polarization potential is small as in the case of the oxygen depolarization in the oxygen cycles, the addition of 0.025% PTFE and 0.025% Dy2O3 additives to electrolyte increase its overpotential, but these two additives can promote the hydrogen evolution at negative plates containing activated carbon (AC), expanded graphite (EG) or flake graphite (FG) with low impurity contents. In the test of cycle life of the 12 V 12 Ah VRLA batteries with the negative plate containing acetylene black (AB), the combined additive of PTFE and Dy2O3 greatly increases the charge efficiency and thus decreases water loss.