Effect of Sodium Fluoride and Sodium Lignosulphonate Additives on Performance of the Soluble Lead Redox Flow Battery

Soluble lead redox flow battery (SLRFB) is a flow battery with a common electrolyte and can be developed in undivided, divided and semi-divided configurations [1]. At present, the development of SLRFB is hindered mainly due to (i) the formation of lead dendrites at anode, (ii) oxygen evolution reaction (OER) at cathode and (iii) accumulation of PbO2 due to poor electrode kinetics [2]. In an earlier study, we have reported a study on extending the cycle-life of SLRFB using an auxiliary electrode concept [3]. In the present study, we report the independent and combined effects of adding sodium lignosulfonate (SLS) and sodium fluoride (NaF) to the electrolyte as anode and cathode benefitting additives, respectively. The study reveals that adding 4.2 gm/L NaF alone improves the kinetics of both electrode reactions as compared to that with no additive but fails to prevent dendrite formation. Adding 1 gm/L SLS alone has beneficial effect on anode by preventing dendrite formation but the concentration of SLS gradually decreases with the cycling of the battery. The combined effect of adding SLS and NaF depends on the concentration of SLS. It is observed that adding low concentration of SLS 0.2 gm/L along with 4.2 gm/L NaF has beneficial effect on both the anode and cathode reactions and hence maintaining this concentration would help extending the cycle-life of SLRFB. The individual as well as combined effects of these additives on the reaction products is studied by quasi in situ XRD and FESEM techniques. The effect on electrode kinetics and cycle life are also reported. References 1. M. Krishna, R.G.A. Wills, A.A. Sha, D. Hall and J. Collins, J. Appl. Electrochem., 48(9) 1031 (2018) 2. D. Pletcher, ECS Transactions, 28(16) 1 (2010) 3. R. Suman, M.K. Ravikumar, N. Jaiswal, S. Patil and A.K. Shukla, ECS Meeting 233, Abstract no. MA2018-01, 221 (2018) Acknowledgements Financial support from UKRI Global Challenge Research Fund project, SUNRISE (EP/P032591/1) and DST, New Delhi is gratefully acknowledged. Figure 1