Internal No-Flux boundary condition

I am modeling a fuel cell with the reacting flow in porous media (rfcs) interface and I would like to make it so H2O is able to transfer through out the entire model, but H2 must remain in the anode compartment and O2,N2 must remain in the cathode compartment. There is a thin membrane separating the anode and cathode compartments where the only species present should be H2O.

I am trying to somehow set a no flux boundary condition for species H2 at the anode compartment/ membrane interface. I also need to set a no flux boundary condition for species O2,N2 at the cathode compartment/ membrane interface.

I think the answer might rest on using an assembly node, but I could really use some help.