Review—Recent Developments and Challenges in Membrane-Less Soluble Lead Redox Flow Batteries

Soluble lead redox flow battery (SLEFB) is attractive for its undivided cell configuration over other flow battery chemistries, which require an expensive membrane/separator. In the SLRFB, lead metal and lead dioxide are plated on the negative and positive electrodes from a single electrolyte reservoir containing soluble lead(II) species. Although the membrane-less cell configuration bestows SLRFB cost-effectiveness over other flow batteries, there are challenges associated with the plating of PbO 2 , Pb dendrite formation and the presence of parasitic reactions. This review mainly focuses on the present status and major challenges of the SLRFB. The solutions to prevent the dendritic growth of Pb metal, accelerate the redox kinetics of Pb 2+ /PbO 2 redox couple, and suppress the oxygen evolution at cathode have been discussed in detail. The role of electrolyte concentration, electrolyte additives, current density, charging time and temperature on the phase change and surface morphology of the PbO 2 electrodeposit has been extensively reviewed. Besides, the modification to the electrolyte in terms of the additive chemistry improving the electrochemical performance and cycle life of SLRFB has been discussed in this review. Finally, the aspects of cell design on improving the performance at a lab-scale as well as stack level are highlighted.