Their hydration properties were measured by TGA: Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ shows the largest water uptake. Their electrochemical performances were characterized using BaCe 0.9 Y 0.1 O 3−δ as electrolyte; polarization resistances as low as 0.5 cm 2 were found at 600 • C, for PrBaCo 2 O 5+δ and Pr 2 NiO 4+δ . The rate determining steps of the oxygen reduction reaction were determined on the basis of electrochemical studies performed as a function of pH 2 O, in air. Proton transfer and water release appear to be the rate determining steps for Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ , PrBaCo 2 O 5+δ and Pr 2 NiO 4+δ . No rate determining step involving proton was found for La 0.6 Sr 0.4 Fe 0.8 Co 0.2 O 3−δ . On the basis of this study, one can suggest that Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ , PrBaCo 2 O 5+δ and Pr 2 NiO 4+δ show some protonic conduction as well as oxide diffusivity and can be labeled Triple Conducting (e-/O 2− /H + ) Oxides, so-called TCO.

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International audienceThe result of the substitution of Pr3+ by Sr2+ in the 214 Ruddlesden-Popper Pr2NiO4+δ material was studied with regard to its electrochemical properties as a H+-SOFC cathode. Structural characterizations as well as physical properties of the Pr2−xSrxNiO4+δ compounds (x ≤ 0.50), in particular hydration as a function of water partial pressure, have shown that oxygen over-stoichiometry and oxygen exchange with atmosphere decrease with increasing x, which has been correlated with the stabilization of the 214 structure by Sr2+ substitution. Electrochemical studies on the oxygen reduction versus hydration have allowed determination of the rate determining steps of the formation of water and evidence the role of protons in Pr2NiO4+δ in contrast to Pr2−xSrxNiO4+δ oxides. It has been concluded that triple mixed conductivity (i.e. protonic, ionic as well as electronic conductivities) exists in this nickelate Pr2NiO4+δ. In addition, there was evidence for strong correlation between the insertion of protonic defects and additional oxygen in the interstitial position of Pr2NiO4+δ

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