Transport properties and phase stability of Ni-doped Pr0.6Ba0.4FeO3-δ as potential symmetrical electrodes for proton-conducting electrochemical cells

BaFeO3-based perovskites have recently attracted considerable attention as a highly promising matrix for the development of robust and electrochemically active electrodes for solid oxide electrochemical cells based on both oxygen-ionic and proton-conducting electrolytes. The excellent redox activity and mixed ionic-electronic conducting behavior of BaFeO3-based materials support their application not only as oxygen electrodes but also as fuel electrodes. In the present study, Pr0.6Ba0.4FeO3-delta is employed as the initial composition, which is then subjected to various Ni-doping strategies until the formation of stoichiometric (Pr0.6Ba0.4Fe0.9Ni0.1O3-delta) and nonstoichiometric (Pr0.6Ba0.4FeNi0.1O3-delta) compounds. The crystal structure, phase relationships, conductivity, and electrochemical activity of these materials have been comprehensively studied in both oxidizing and reducing atmospheres in an effort to identify the best doped derivatives. The experimental results demonstrate that Ni doping represents a promising approach to increase the electrochemical activity of the origin electrode, as evidenced by the observed improvement in electrical conductivity in oxidizing atmospheres and the formation of electrocatalytically active exsolved particles in reducing atmospheres. At the same time, the stoichiometric composition results in superior electrode performance relative to the non-stoichiometric composition, indicating that conventional co-doping of ABO3 perovskites may prove more advantageous than B-excess (or A-deficient) analogs. Therefore, this work elucidates the intricate composition-structure-property relationships of barium ferrite materials fort their further high-temperature electrochemical applications.