Improved surface proton conduction of yttrium-stabilized zirconia via acidic modifications

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 X-ray diffraction, high-resolution transmission electron microscope, element analysis, infrared spectra, N2 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 m2 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.