A method of forming a composite structure for an ion transport membrane in which a filler substance is applied to one surface of a porous support layer in order to plug pores and prevent coated ion conducting material from penetrating the pores to reduce the amount of gas diffusion. Prior to coating of the surface with layers that may be oxygen ion conducting layers, excess filler substance is removed. After the coating of the one surface, the filler substance is removed from pores.
 This invention was made with United States Government support under Cooperative Agreement number DE-FC26-01NT41096 awarded by the U.S. Department of Energy, National Energy Technology Laboratory. The United States Government has certain rights in this invention.