Fabrication of Yttrium Doped Barium Zirconate for High Performance Protonic Ceramic Membranes
Barium zirconate has emerged as the leading candidate material for fabricating dense ce ramic membranes for hydrogen separation. B sites in the ABO3 perovskite are acceptordoped with a +3 cation most commonly yttrium charge compensated by the formation of oxygen ion vacancies in the lattice. A minor fraction of B sites can be filled with cerium to give BaZr0.9 xCexY0.1O3 d, x 0.2. Upon hydration at elevated temperatures, weaklybound protons are formed in the lattice. This produces a cubic perovskite ceramic proton conductor useful in diverse applications, such as protonic ceramic fuel cells, electrolysers, and catalytic membrane reactors operating at temperatures between 600 and 800 degC. A necessary requirement for fabricating thin ceramic membranes for proton diffusion is to maximize grain size while eliminating percolating porosity. However, high density, large grained barium zirconate is a very difficult material to prepare by traditional pow der sintering methods. This chapter describes a new methodology for making protonic ceramic membranes with large grains and virtually no residual porosity. This discovery has the potential to have a profound impact on energy conversion efficiency of the vari ous membrane devices envisioned for the coming hydrogen energy economy.