An analysis of the thermodynamic conditions at the interface between the two electrolytes was prompted by the criticism found in the literature concerning the use of a bi-electrolyte galvanic cell as an advanced CO2 sensor. It turns out that, according to the data for the standard free enthalpies of formation of the phases involved, a reaction to a thermodynamically more stable compound is unlikely. Even if such a reaction took place, the conditions relevant to the electrochemical behaviour of the cell would not be adversely affected. From this point of view the bi-electrolyte cell is without any doubt a promising approach for a smart CO2 sensor. The only aspect that could be a restriction to the applicability of such a cell is the Na2O enrichment at the inner interface resulting from the electronic transference through both of the electrolytes.