  We present a generalization of the Debye-H\"uckel free-energy-density
functional of simple fluids to the case of two-component systems with arbitrary
interaction potentials. It allows one to obtain the two-component
Debye-H\"uckel integral equations through its minimization with respect to the
pair correlation functions, leads to the correct form of the internal energy
density, and fulfills the virial theorem. It is based on our previous idea,
proposed for the one-component Debye-H\"uckel approach, and which was published
recently \cite{Piron16}. We use the Debye-Kirkwood charging method in the same
way as in \cite{Piron16}, in order to build an expression of the free-energy
density functional. Main properties of the two-component Debye-H\"uckel free
energy are presented and discussed, including the virial theorem in the case of
long-range interaction potentials.
