Homogenization of Poisson-Nernst-Planck equations for multiple species in a porous medium

Abstract: The Poisson-Nernst-Planck (PNP) equations form a coupled parabolic-elliptic system, which models the transport of charged particles under the influence of diffusion and electric force. In this paper, we rigorously derive a homogenized model for the PNP equations, for the case of multiple species, defined on a periodic porous medium in spatial dimensions two and three. This extends the previous homogenization results for the PNP equations concerning two species. Here, the main difficulty is that the microscopic concentrations remain uniformly bounded in a space with relatively weak regularity. Therefore, the standard Aubin-Lions-Simon-type compactness results for porous media, which give strong convergence of the microscopic solutions, become inapplicable in our weak setting. We overcome this problem by constructing suitable cut-off functions. The cut-off function, together with the previously known energy functional associated with the system, gives us equicontinuity of the microscopic concentrations on the part of the domain where the values of the concentrations do not exceed the height of the cut-off function. Moreover, it turns out that, on the remaining part of the domain where the concentrations are larger than the height of the cut-off function, the application of the energy functional is enough in order to obtain equicontinuity. These arguments eventually yield strong convergence of the microscopic concentrations in $L^1_t L^r_x$, for some $r>2$, enabling us to pass to the limit in the nonlinear drift term. Finally, we derive the homogenized equations by means of two-scale convergence in $L^p_t L^q_x$ setting.