High-Temperature Proton Conductors Based on Strontium and Barium Cerates: The Content, Interphase Exchange, and Diffusion of Hydrogen

The hydrogen content and hydrogen exchange kinetics of doped cerates of strontium and barium are studied in a reducing environment by the isotope balance and isotope exchange techniques. The measurements are performed at 500-840°C and hydrogen pressures of 2.7-16 gPa. The interphase exchange of hydrogen is found to occur at high speed via dissociative mechanisms. The effective activation energy for the hydrogen heteroexchange is determined. The diffusion coefficient for hydrogen in BaCe0.95Nd0.05O3-δ is computed. The hydrogen content per formula unit appears to equal 0.48 ± 0.05 in SrCe0.95Y0.05O3-δ and 0.60 ± 0.05 in BaCe0.95Nd0.05O3-δ at 550 and 720°C, respectively, and a hydrogen pressure of 6.7 gPa. This is much greater than in an oxidizing environment, where the hydrogen content in an oxide is approximately proportional to the doping level of sublattice B. A possible explanation is connected with the presence of Ce3+ ions in the oxides or the dissolution hydrogen in a neutral form.