Effect Of Bi, In On The Electrochemical Behavior Of Zinc Electrode In Alkaline Electrolyte

Zinc is one of the most commonly used battery electrode materials because of itslow equilibrium potential, reversibility, compatibility with aqueous electrolytes, lowequivalent weight, high specific energy, high volumetric energy density, abundance,low cost, low toxicity, and ease of handling. Zinc has mainly been used in primary(nonrechargeable) batteries, but great developments have been made to allow zinc tobe more widely used in secondary (rechargeable) batteries, especially for the alkalinezinc battery. Based on the current status of the research and development of zincelectrode in alkaline electrolyte, in this work, the electrochemical behavior of purezinc and zinc alloy containing Bi and In in 35%KOH alkaline solutions has beeninvestigated by the electrochemical methods, including Tafel linear polarization,potentiodynamic polarization, cyclic voltammetry, discharge measurements underconstant current density and potentiostatic polarization, combined with scanningelectron microscopy (SEM). It is emphasized on study of the effect Bi and In on theelectrochemical behaviors of zinc electrode. And the mechanism and function ofaddition of Bi and In elements in zinc electrode has been preliminary discussed. Themain results and progress of this work are listed as following:(1) It is indicated that the open circuit potential of zinc electrode shifts positivelyand the anodic current density and passive current density increase after the bismuthaddition. The discharge measurement shows that the addition of bismuth shortens thetime to passive state of zinc alloy electrodes at the same conditions compared to purezinc. The addition of Bi will enhance the electrochemical activity for zinc alloyelectrode, and the concentration of zincate ions is high at the interface ofelectrode/electrolyte, which accelerate the precipitation of the zincate ions on theelectrode surface. And when the concentration of zincate ions exceeds the solubility ofzinc oxide in the alkaline electrolyte, the passivation will take place on the electrodesurface. The addition of Bi also raises the current-increase and accelerates the growthof zinc dendrite. (2) It is found that the open circuit potential of zinc alloy electrode shifts positively and the anodic current density and passive current density increase when adding In element to zinc electrode. And the addition of In shortens the time to passive state of zinc alloy electrodes at the same conditions compared to pure zinc, due to the fast anodic dissolution of zinc alloy electrodes and the high concentration of zincate ions at the interface of electrode/electrolyte, which accelerate the precipitation of the zincate ions on the electrode surface. When the concentration of zincate ions exceeds the solubility of zinc oxide in the alkaline electrolyte, the passivation will take place on the electrode surface. After dissolution of zinc-indium alloys, In³⁺will react with the alkaline electrolyte rapidly and form the indium oxide or indium hydroxide and precipitate on the electrode surface. The zinc electrode with In shows a rougher surface due to a fast anodic dissolution, and which will increase the surface area of electrode and enhance the anodic activity of zinc-indium alloys electrodes. And the addition of In may changes the distribution of current density and Zn(0H)4 " on the electrode surface, and accelerates the growth of zinc dendrite.(3) Because of positive potential for both Bi and In, the open circuit potential of zinc alloy electrode with Bi and In shifts positively and the anodic current density and passive current density increase obviously, especially for the 0.02%Bi+0.02%In zinc alloy electrode. It is found that the open circuit potential shift negatively and the crystal particles decrease when the Bi or In content exceed 0.05%. The addition of bismuth and indium shortens the time to passive state of zinc alloy electrodes at the same conditions compared to pure zinc, that is the addition of Bi and In will enhance the electrochemical activity for zinc alloy electrodes. The addition of Bi and In will accelerate the growth of zinc dendrite more strongly than the addition Bi or In element alone in zinc electrode.