Concentration cell

A galvanic cell whose reversible electromotive force arises from different reactant activities at otherwise corresponding interfaces. The Nernst equation relates the measured voltage to the activity ratio, provided the transported charge and reaction stoichiometry are specified.

A cell comparing oxygen chemical potentials across an oxygen-ion-conducting electrolyte. With oxide-ion conduction and four electrons transferred per oxygen molecule, $E=RT\ln (p_2/p_1)/(4F)$ for consistently ordered terminals. Reference pressure, interface equilibrium and electronic leakage must be controlled.