The GMPNP (equations ( )-( )), PNP (equations ( )-( ) in the SI) as well as the reaction-diffusion system (equations ( ) and ( ) in the SI) are solved using the finite element method for spacial discretization and a backward Euler scheme for temporal discretization. The simulation domain in 1D is depicted in Figure in the SI. The backward Euler scheme, although computationally more intensive, was found to be necessary considering the stiff nature of both the PNP and GMPNP system of equations. We use the Python package FEniCS project to solve the weak Galerkin form of the transient non-linear GMPNP system such that the mass balance equation ( ) and the Poisson equation ( ) are solved self-consistently using the Newton method till a steady-state is reached.