Extending cycle life of the soluble lead redox flow battery with an auxiliary gas-diffusion electrode: a proof-of-concept study

Development and demonstration of soluble lead redox flow battery (SLRFB) is hindered due to its limited cycle life caused by the formation of lead dendrites, oxygen evolution reaction (OER), and accumulation of PbO2 sludge. OER leads to an imbalanced deposition of Pb metal at anode and PbO2 at cathode. As a result, complete oxidation of Pb is stalled during discharge of SLRFB. Besides, sluggish kinetics of cathode reaction results in accumulation of PbO2. Due to incomplete dissolution and accumulation of both active materials, concentration of Pb2+ decreases continuously in the electrolyte. Under such conditions, repeated charge–discharge cycling leads to the failure of SLRFB. In this study, we propose and demonstrate a novel route of using an auxiliary gas-diffusion electrode to obviate these problems to help in extending the cycle life of SLRFB. The auxiliary electrode is operated either as an air electrode or a hydrogen electrode. When the auxiliary electrode is an air electrode, it is used as positive electrode, and on coupling with anode of SLRFB, it forms a galvanic Pb–air flow cell that on discharge helps in oxidizing Pb metal to Pb2+ ions. When the auxiliary electrode is a hydrogen electrode, it is used as negative electrode, and on coupling with cathode of SLRFB, it forms a galvanic H2–PbO2 flow cell which on discharge reduces PbO2 to Pb2+ ions and mitigates the adverse effect of sludge accumulation in SLRFB.