Hydrogen permeability in sintered CeO2 at high temperatures

It was found that the sintered CeO2, which was not perovskite-type but fluo rite-type, permeated hydrogen under H-2-H2O atmosphere at 1050-1800 K. Thre e tube-shaped specimens (phi 0.287 x 0.894 cm) (SP I, SP II, SP), the lengt hs of which were 1.40, 0.37, and 1.45 cm, were prepared. The nonexistence o f micropores in specimens was confirmed by supplement of He (11.2%) + N-2 t o the outside of SP at 1650-1820 K. H-2 (7.90%) + H2O (2.55%) + N-2 was sup plied to the outsides of SP I and SP II and Ar gas was allowed to flow to t he inside of them. The flow rate to SP I was 21.2 cm(3) min(-1), and the fl ow to SP II was controlled so that the hydrogen concentrations measured by a gas chromatograph were of the same value. After the calculation of H-2, H 2O, and O-2 Concentrations in an equilibrium state inside and outside SP I and SP II and the elimination of mechanically leaked H-2 and permeated hydr ogen through the supporting materials (Pt rings, alumina tube, and disk), t he atomic hydrogen permeability, J(H), was determined. The hydrogen partial pressures in the outside and inside were 7.90 x 10(-2) and 7.43 x 10(-5) t o 1.53 x 10(-3) atm at 1050-1800 K. Log(J(H) mol h(-1) cm(-1)) increases wi th rising temperature, T, while it is not proportional to 1/T. As the elect ronic conduction in CeO2 is considerably higher at low oxygen partial press ure, there is a possibility that CeO2 is an electron-proton mixed conductor under H-2-H2O atmosphere at high temperatures. (C) 1999 The Electrochemica l Society. S0013-4651(98)03-097-3. All rights reserved.