The effect of crystal orientation on aliovalent dopant segregation at the surface of La 0.6 Sr 0.4 CoO 3 as a model perovskite oxide was investigated. La 0.6 Sr 0.4 CoO 3 pellets were produced and then annealed in air at 800 C for 2-5 hours to drive the cation segregation at the surface. To quantify the chemical state of the pellets' surface, including cation composition and secondary phase precipitates rich in Sr, the pellets were characterized by X-ray photoelectron spectroscopy and Auger electron spectroscopy. To systematically assess the correlation between crystal orientation and dopant cation segregation, selected regions at the surface of the annealed pellets were analyzed by scanning electron microscopy and electron backscatter diffraction. Investigation of more than 300 grains revealed that the area coverage of the Sr-rich precipitates on grains having a {001} orientation was more than 3 times higher compared to that on the {101} and {111} orientations. On the other hand, the number density of precipitates was very similar on each grain orientation. This grain orientation dependent behavior indicates that the exposed facet plays an important role in dopant cation segregation, especially in the growth of secondary phases, likely by altering the surface energy and charged defect concentration. The present study provides insights into the importance of atomic arrangements in determining the surface stability and cation segregation tendency on perovskite oxides.

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There is a considerable interest in lowering the operating temperature of solid oxide fuel cells. In this respect, (La,Sr)CoO 3 -(La,Sr) 2 CoO 4 dual phase oxides have attracted much attention as cathode materials due to their enhanced oxygen reduction reaction kinetics. The main drawback in lanthanum strontium cobaltite cathodes is Sr-segregation at operating temperatures which causes a sudden degradation in performance. In the current study, this segregation is verified by a specially designed experiment where a (La 0.8 Sr 0.2 )CoO 3 -(La 0.5 Sr 0.5 ) 2 CoO 4 bilayer is deposited and annealed for an extended period of time. Thin film cathodes are then deposited via co-sputtering of (La 0.8 Sr 0.2 )CoO 3 and (La 0.5 Sr 0.5 ) 2 CoO 4 yielding non-crystalline structures with acceptable area specific resistance values at temperatures as low as 575°C. The stability of these cathodes is investigated over an extensive range of compositions (La 0.8 Sr 0.2 )CoO 3 : (La 0.5 Sr 0.5 ) 2 CoO 4 = 0.10:0.90 -0.90:0.10. Prolonged annealing of cathodes at temperature of the same initial area specific resistance shows an exceptionally stable cathode performance as measured by electrochemical impedance spectroscopy responses. It is therefore concluded that co-sputtered (La 0.8 Sr 0.2 )CoO 3 -(La 0.5 Sr 0.5 ) 2 CoO 4 dual phase cathodes with their amorphous/nanocrystalline structures, especially at mid-compositions, provide an extremely stable microstructure with a strong resistance to Sr segregation.

Summary Perovskite‐based electrocatalysts are extensively investigated as a replacement for noble metals electrocatalysts for energy storage and conversion devices. Their interesting catalytic activity, low cost, and diversity are considered major advantages. In this work, a facile dual‐doping strategy has been conducted and yielded an astonishing upgrade of lanthanum cobaltite; fine‐tuning of both A and B sites with calcium and manganese has proven remarkably beneficial. The dual‐doping modulates the electronic configuration of both transition metals and raises the oxygen vacancies. Consequently, oxygen evolution reaction has been assessed and La0.8Ca0.2Mn0.2Co0.8O3 showed significantly improved overpotential and maximal current density in comparison with pristine LaCoO3. Furthermore, the ZAB exhibited a high open circuit potential and superior charge‐discharge cyclability, compared to Pt/C‐based electrodes. The current work explores the influence of simultaneous doping of the A and B sites in lanthanum perovskite oxides on electrocatalytic performance to encourage further exploration of such an approach in electrocatalysis. Novelty statement Simultaneous Ca and Mn dual‐doping of LaCoO3 in the A and B sites were successfully applied. The effects on the crystal structure, oxidation states, and electrocatalytic activity were studied. LCMC8228‐based ZAB has achieved a large discharge capacity of 88.1 mAh in comparison to the benchmark.