Polyaniline and Polypyrole as Cathode Materials for Zinc Batteries in Chloride and Chloride/citrate Based Electrolytes

Electrochemical behavior of zinc, thin polyaniline (PANI) and polypyrole (PPy) electrode polymerized from 0.1 M HCl and 0.1 M aniline or 0.1 M pyrole on graphite electrode, in 0.2 M ZnCl₂ and 0.50 M NH₄Cl (chloride electrolyte) and with addition of 0.33 M Na-citrate (chloride/citrate electrolyte) were investigated. In the range of investigated charge/discharge current densities of 0.25 to 1 mA cm^-2, initially obtained specific capacity of PANI electrode was in the range of 140 to 85 mAh g^-1, respectively. Specific capacity and columbic efficiency were affected with anodic potential limits. For anodic potential limits of 0.32 V (SCE) citrate/chloride electrolyte shows better characteristic than chloride electrolyte, due to the influence of citrate ions on negative shift of doping reaction. Increasing anodic potential limit to 0.5 V (SCE), leads to faster decrease of specific capacity in citrate/ chloride than in chloride electrolyte, which was explained by higher hydrophilic effect of citrate anions. PPy electrode shows similar charge/discharge characteristics in chloride and in chloride/citrate electrolyte. In the range of investigated current densities of 0.1 to 0.75 mA cm^-2, discharge electrode capacity was in the range of 0.075 to 0.045 mA h cm^-2 or 100 to 60 mA h g^-1, respectively. For the same synthesis and operating conditions PANI electrode shows much better electrochemical characteristic than PPy electrode. In the chloride/citrate comparing with chloride containing electrolyte zinc electrode shows negative shift of the open circuit potential of ~130 mV, decreases of exchange current density for more than order of magnitude and increase of cathodic Tafel slope, due to the zinc ions complexation. In citrate/chloride electrolyte zinc dendrite formation were suppressed.