A modular arrangement for stacks of ion conducting electrolyte elements includes a plurality of solid state ion conducting electrolyte elements spaced apart and arranged into stacks and the stacks further arranged at regular intervals around a central plenum. A plurality of gas flow passageways are disposed in the spaces between the electrolyte elements to enable reactant gases to circulate between the elements. A pair of manifold plates are disposed on either side of the electrolyte elements and sandwich the elements therebetween.