Convection Influences the Charging Dynamics of Porous Electrodes

Electrolyte-immersed porous electrodes are essential for various electrochemical technologies and subject to ongoing research. Most theories for porous electrode charging consider only diffusion and electromigration as ionic charge transport mechanisms. However, the charging process can induce a fluid flow causing additional convective charge transport, whose influence on the charging dynamics of porous electrodes is unknown so far. Here, we simulate the charging using the fully coupled modified Poisson-Nernst-Planck and Navier-Stokes equations for a single cylindrical pore next to a reservoir. The simulations show that convection caused by an induced fluid flow can substantially speed up the charging of porous electrodes. Furthermore, we present a semi-heuristic analytical model describing the induced fluid velocity and the electric current arising from convection. We demonstrate the model’s applicability for moderate applied potentials and that, in this regime, convection speeds up charging most for pore radii roughly ten times larger than the Debye length. Our results show that neglecting convective effects when studying the charging dynamics of porous electrodes is often not realistic, which opens a direction for future research.