s This work studied the acidic surface modifications on the conduction properties of yttrium-stabilized zirconia (YSZ) nanocrystals using sulfuric and phosphoric acid protonation techniques with an aim to discover suitable additives of the proton-conducting membranes for intermediate temperature operation. All YSZ nanostructures were hydrothermally prepared and the sample surfaces were modified with sulfate or phosphate groups by subsequently immersing the as-prepared samples into sulfuric or phosphoric acid. The obtained samples were characterized by Xray diffraction, high-resolution transmission electron microscope, element analysis, infrared spectra, N-2 adsorption/desorption, and impedance spectroscopy. It was found that the samples exhibited a cubic fluorite structure with a grain size of 4.5 nm and a high surface area of 205 m(2) g(-1). Proton conduction measurements showed that sulfate-modified samples had an apparently low proton conductivity, while the phosphate-modified ones exhibited a significant proton conductivity and improved thermal stability. These observations were explained by taking into account the grafted species and the amount of hydrated water. (c) 2007 Elsevier B.V. All rights reserved.