Effect of anionic, cationic and non-ionic surfactants with NaF as binary additives on the performance of soluble lead redox flow battery

The effect of adding sodium lignosulfonate as anionic, hexadecyltrimethylammonium p-toluene sulfonate (HDTMA p-TS) as cationic, or Triton X-100 as non-ionic surfactant along with NaF into the electrolyte as binary additives on the performance behaviour of a soluble lead redox flow battery (SLRFB) is studied by Field Emission Scanning Electron Microscopy (FESEM) and various electrochemical techniques. The FESEM studies show no significant change in the structural morphology of PbO2 deposits in the case of cationic surfactant in conjunction with NaF, whereas sodium lignosulfonate and Triton X-100 in conjunction with NaF show significant changes in the morphology of cathode deposits. FESEM studies reveal that cationic surfactant with NaF facilitates the smooth and lateral growth of Pb deposits. Cyclic voltammetry and kinetic studies show that adding NaF to anionic surfactant is detrimental, while it is found to be beneficial with cationic and non-ionic surfactants. The constant current charge and discharge cycling studies show that cells with pristine electrolyte, anionic surfactant along with NaF, Triton X-100 along with NaF additives show a cycle-life of 25, 75, and 25 cycles, respectively, when charged at 20 mA cm−2 current density and discharged to 0.8 V at the same current density. Interestingly, the cationic surfactant with NaF exhibits a cycle-life of more than 1350 cycles without any maintenance with no deterioration in the performance under similar conditions. To the best of our knowledge, this is the highest cycle-life demonstrated for SLRFB system without any maintenance. Mechanistic insights for the beneficial role of cationic surfactant in controlling Pb dendrite formation are discussed.