Nowadays the development and the implementation of green energy sources become extremely important. Substituted beta-aluminas are regarded as attractive materials for the use as proton conducting solid electrolyte (SE) in low- and intermediate temperature fuel cells. Thus, the aim of the work was to study the phase composition, structure, and transport properties of H-β-Al₂O₃ ceramics. Precursor of Na₂O·6.5Al₂O₃ composition was manufactured via pyrolysis, compacted into the pellet (diameter of 30 mm, thickness of 5 mm)  at pressure 10 tons and annealed at 1520 ºC for 2 hours. H-β-Al₂O₃ SE was obtained by ion exchange technique of Na-β-Al₂O₃ membrane in HNO₃ and H₂O at the room temperature. Ion exchange was controlled in water using conductometry (inoLab Cond7110) and in acid using atomic emission spectroscopy (ICPE-9000). The degree of substitution of Na⁺ for H⁺ in an acidic medium was calculated to be 17%. Structure of proton substituted beta-alumina SE was examined by XRD (SHIMADZU XRD-6000), hydrostatic weighing (RADWAG WAS 220/X), SEM and EDX techniques (Hitachi S-3400N). The transport properties of SE were investigated using EMF method at three different initial concentrations (0.1, 0.2 and 0.4 M) of hydrochloric acid and potassium hydroxide.

The Na⁺ to H⁺ exchange results in the peaks intensity enhancement in the XRD pattern without shifting their positions. All reflexes on the X-Ray pattern correspond to the protonated phase of β-alumina. Via SEM and EDX it was found that both β- and β?-alumina are present in the SE structure. The sodium cation is exchanged by a proton in the β-alumina phase only, no substitution occurs in sodium β?-alumina phase. The density was measured by hydrostatic weighing before and after the exchange. The diffusion and self-diffusion coefficients were calculated from the EMF data for the proton and potassium cation. For a proton, they are equal to D_diff(H⁺)=1.19±0.29×10^-4cm²/sec and D_self-diff(H⁺)=1.7×10^-6cm²/sec, and for K⁺ D_diff(K⁺)=3.36±0.57×10^-4cm²/sec and D_self-diff(K⁺)=5×10^-7cm²/sec. The values obtained correlate well with the literature [1]. It was suggested that proton transport takes place through the β-alumina phase and Cl^- transport takes place through β?-alumina phase.

Acknowledgements.
SEM and EDX data were obtained at «GEOMODEL» center, AES measurement was performed at «Center for Chemical Analysis and Materials Research» and XRD data was obtained at «Research Centre for X-ray Diffraction Studies» at SPBU Research Park.

References
[1] Yao Y. F. Y., Kummer J. T. Journal of Inorganic and Nuclear Chemistry. 1967, ?. 29, ?. 9, 2453-2475.