The conditions under which it is possible to overcome the thermodynamic constraints of the reversible reaction : A + nH(2) <-> mB, using a solid state H+ cell, are examined. Three reactor types are considered, a plug flow reactor, a well-mixed reactor and a ’single-chamber’ cell. The key parameters that affect reaction conversion are identified. Experimental results for the reaction of methane dimerization studied with a strontia-ceria-ytterbia electrolyte on Pd and Ag electrodes, are presented.