Abstract
This chapter is focused on nanocomposites based on ionomers. Material developments are described mainly aiming two applications: actuators and fuel cells. For fuel cells, nanocomposites can help in obtaining membranes for direct alcohol fuel cell with low-alcohol permeation and in the preparation of polymeric membranes for use in hydrogen fuel cell operating at low humidity levels and high temperatures. An additional task for nanocomposites is to improve the membrane-electrode layers, giving a better contact and better distribution of catalysts in the membrane.