Preparation of Nanoparticle Core−Shell Electrolyte Materials for Proton Ceramic Fuel Cells

Abstract

The sinterability of yttrium-doped barium zirconate (BZY) has been improved through an original synthesis approach giving a core−shell type arrangement in which nanoparticulate BZY is enrobed by a thin coating of yttrium-doped barium cerate (BCY). A flash combustion route was first used to prepare BZY10 (10% yttrium-doped) in a nanopowder form with average particle diameter of 12−17 nm. The nanoparticles were then dispersed in a hydrogel generated from 3,3′,3′′-nitrilotripropionic acid complexed metal (yttrium, barium, cerium) acrylates. After thermal elimination of the organic moieties, a material of novel macroscopic architecture is obtained, which can be densified (apparent density ≥ 97%) by sintering compacted pellets at 1300 °C for 10 h, i.e. some 200 °C lower than is generally used to densify BZY. X-ray diffraction indicates that two phases corresponding to BCY10 and BZY10 are present and that no discernible migration of atoms occurs between the zirconate core and the cerate shell. Proton conductivities of densified pellets were determined in a moist nitrogen atmosphere in the range 300−600 °C using impedance spectroscopy. The total conductivity is in the range 4.1 × 10−4 S/cm (300 °C)−9.5 × 10−3 S/cm (600 °C), which is an order of magnitude higher than that of BZY10, prepared under equivalent conditions and the core−shell material displayed improved stability against carbonate formation in a CO2 atmosphere. The densification, proton conductivity, and CO2 uptake properties of the novel core−shell structured proton ceramic all differ from those of yttrium-doped barium zirconate cerate solid solution containing a similar ratio of yttrium, zirconium, and cerium, and of a physical mixture of BCY10 and BZY10, and show an improved set of properties compared with those of BCY10 or BZY10 alone.