Ceramic membranes derived from carboxylate-ferroxane nanoparticles are shown to yield high power (5.21 mW cm(-2)) and current (16.5 mA cm(-2)) densities in a working membrane electrode assembly, comparable to those obtained using untreated Nafion (R) membranes. The ceramic membranes have a high density of surface hydroxyl sites, conducting protons by a mechanism consistent with Grotthuss diffusion that is nearly insensitive to humidity over a range of 33-100% RH. (C) 2008 Elsevier B.V. All rights reserved.