The first term of the rhs of this equation is the isotropic potential due to the nanoparticle, whereas the other contributions represent the potential due to the ionic species. The same result can be easily obtained by a direct application of the Gauss Law and the underlying radial symmetry. The electrostatic potential is set to zero at the cell boundary r = R c , where the electric field also vanishes due to the overall charge neutrality inside the SHC. The lhs of Eq. ( ) can be interpreted as the electrochemical potential of ionic specie i at position r. The equilibrium condition then establishes that this electrochemical potential must be constant everywhere. Relation (10) leads to the following equilibrium concentrations: