Designing Isothermal Natural Convection Dominated Electrochemical Cells: Experimental Validation

Deposition/dissolution redox reactions in electrochemical cells, such as soluble lead redox batteries, induce strong natural convection flow in the electrolyte. The Rayleigh number range encountered in these systems where the flow field is set up due to concentration-gradient-driven density gradients is uncommon in thermal systems, by virtue of naturally large values of Schmidt number, as compared to Prandtl number. In this work, we report the first direct PIV measurements of natural convection electrolyte solutions for soluble lead redox chemistry cells and compare them with the predictions of the existing models. We directly test the assumption of 2-dimensional flow by experimenting with low aspect ratio cells of different cell widths. A comparison of the model-predicted individual electrode potentials with measurements carried out in this work shows the adequacy of the fitted parameters, which have remained unchanged after their introduction in the context of a flow-through battery. We further tested the model by comparing predictions for several new configurations with experimental measurements. The new configurations include tall cells, cells with significant electrode gaps, cells provided with extra space at the top or below the active zone between electrodes, and intermittent mixing between charge and discharge. The new configurations bring further insights into how the multiple physics interact in soluble lead redox chemistry-based cells. Our measurements of cell potential profiles validate the model predictions in all cases.