Suppression of electroconvection due to van der Waals attraction of polymers dissolved in an electrolyte towards a metal electrode

Electroconvection enhances non-planar deposition on the surface of electrodes and reduces the life of batteries. Polymers with modest molecular weights dissolved in the bulk electrolyte are attracted to the metal electrode due to weak van der Waals forces of attraction. This results in a thin (order 10-100 nm) layer with a higher concentration of dissolved polymers near the ion-selective surface. The van der Waals force acting on the polymers acts as a restoring body force that opposes the growth of incipient convective motions. Using linear stability analysis and numerical simulations, we show that this restoring body force increases the critical voltage for the onset of electroconvection and reduces the growth rate of electroconvective modes above the critical voltage. Analysis of quartz crystal microbalance (QCM) experimental results confirms the presence of a polymer layer near the metal electrode. The variation of the time required for the onset of significant electroconvective motions as a function of applied voltage in experiments is compared to the variation predicted by our analysis.