Effect of binary additives on performance of the undivided soluble-lead-redox-flow battery

Abstract

Cycle-life of Soluble-Lead-Redox-Flow-Batteries (SLRFBs) is impacted due to formation of lead dendrites at anode and oxygen evolution at cathode. In this regard, addition of certain surfactants to the electrolyte helps preventing dendrite formation while adding fluoride salts reduces the rate of oxygen evolution reaction. Since SLRFB has a common electrolyte, understanding the combined effect of such additives on individual electrodes as well as on the overall SLRFB performance is desirable, which is lacking in the literature. Accordingly, in the present study, the combined effect of sodium lignosulfonate (SLS) and sodium fluoride (NaF) additives on the overall cell performance, individual electrodes, electrode kinetics, crystallographic phase formation, and surface morphology of electrodeposits is reported. The electrochemical data on SLRFB are analyzed in the light of electrode-kinetic parameters, namely limiting current-density, exchange current-density and Tafel-slope. The study reveals that adding NaF additive enhances the kinetics of Pb/Pb2+ and Pb2+/Pb4+ redox couples as compared to the pristine electrolyte or with SLS additive. The exchange current-density is higher with NaF additive as compared to NaF and SLS binary combined additive. It is also observed from cyclic voltammograms that the peak current decreases in the presence of binary additive indicating sluggish electrode kinetics. SEM images and galvanostatic charge–discharge studies suggest that binary additive results in uniform electrodeposit which improves the cycle-life of SLRFB.