Transport of diluted species and electrostatics

Dear Community,

I am trying to combine the physics of the poisson equation (electrostatics) with the nernst-planck (transport of diluted species) in Comsol 4.1 for like 6 weeks now, and all I get is errors. Does anyone have experience with these two models combined?

Eventually I wanna model the concentration and potential and flux fields in a nanopore, but I took a step backwards, and just try to get the physics right, by modeling an electrical double layer next to a charged surface.

Some details on my model. I use the potential field from the electrostatics as input for the potential in the nernst-planck, and in return I defined a space charge density of F*(c-c2) (c and c2 being the electrolyte ions) for the electrostatics. That should be enough to couple the two physics, or am I wrong?
Moreover I have a -1 mC/m2 surface charge on one side and ground on the other side (just rectangle). Electrolyte concentrations are fixed on the ground side to 1 mM.

All I get as error is that the maximum number of newton iterations is reached and the solution is not converged. I tried a whole bunch of different initial conditions and solver configurations, but nothing is working.

Does anyone have any ideas?

Best
Nils