Concentration Gradient Driven Natural Convection in Soluble Lead Redox Flow Batteries

Abstract

Low cost and long cycle-life energy storage systems are needed to harness renewable sources of energy at large scale. Among the options available, redox ow batteries (RFB) offer the maximum potential. The vanadium based RFB offers long cycle life but requires high initial investment and running cost. The membrane-less soluble lead redox ow battery (SLRFB) offers a low cost alternative. Since it uses a common electrolyte for both the electrodes without a proton exchange membrane in-between, it is likely to be easy to operate and maintain. Soluble lead redox ow battery (SLRFB) is currently under development. Our group has earlier established the dominant role concentration gradient driven natural convection ow plays in this electrochemical system. The present work focuses on developing new designs that harness natural convection flow for effcient charge-discharge operation of a single SLRFB cell. We take fi rst step in this direction by establishing the ability of a model developed in our group to match experimental measurements. The validated model is then used to test new designs for cell and electrodes. The model considers fluid flow, potential eld, electro-deposition and electro-dissolution reactions on electrode surfaces, buildup of deposits, and transport of ionic species under convection, diffusion, and electric fi eld induced migration. The highly coupled physics makes simulations computation intensive, hence 2-d approximation is used. A batch cell with wall mounted electrodes (standard cell) and additional electrolyte above (top) and below (bottom) them is studied for model validation. The simulation results are obtained without re tting any parameters, and are shown to be independent of grid size. The results con rm natural convection induced electrolyte circulation. The strong circulation predicted on anode compared to cathode is attributed to electric field driven migration of Pb2+ being opposed to diffusional flux on anode and in the same direction on cathode. The cell potential during charge remain...