Hydrogen permeability of YSZ single crystals at high temperatures

The atomic hydrogen (H) permeability, J H, of 10YSZ single crystal (fluorite-type) was measured at 1800–1050 K using the Nigara-method. Two tubular specimens (φ 1.30×0.93 cm; length: 3.35 cm (Specimen(L)) and 1.00 cm (Specimen(S))), annealed at 1570 K for 6 h in air, were used to eliminate the permeations of supporting materials (Pt rings, alumina tube, and alumina disk). Measurement was carried out after the specimen had been kept at 1800 K for 20 h. The J H was 3.97×10 −7–2.79×10 −9/mol h −1 cm −1, when it was assumed that P H 2 =7.36×10 3 Pa and P H 2O =2.30×10 3 Pa outside of both specimens and that the Ar flow rates to the inside of Specimen(L) and Specimen(S) were 21.5 and 16.9–19.9 cm 3 min −1, respectively. Log J H decreased with the decrease of temperature and was proportional to the inverse temperature. The activation energies were 0.61±0.09, 1.60±0.05, and 0.79±0.02 eV at 1800–1680, 1680–1330, and 1330–1050 K, respectively. The protonic conductivity, which was roughly calculated from the J H and the hydrogen partial pressures inside and outside of the specimens, was 2.4×10 −6–1.5×10 −8/S cm −1 at 1800–1050 K. The J H of other 10YSZ single crystal specimens, which were not annealed and which were measured after being kept at 1800 K for 1 h, was lower than that of the above specimens, especially at high temperatures, and the activation energies were 1.27±0.03, 0.15±0.03, and 1.49±0.09 eV at 1800–1425, 1425–1150, and 1150–1050 K, respectively. The 10YSZ single crystal would be an electron–proton mixed conductor under H 2–H 2O atmosphere at high temperatures. Since the J H of 12YSZ single crystal specimens, which were annealed at 1870 K for 24 h in air and were measured after being kept at 1800 K for 18 h, was less than 1×10 −9/mol h −1 cm −1 at 1800 K, it was difficult to determine the relation between its hydrogen permeability and temperature.