Controlling crystal orientation in multilayered heterostructures toward high electro-catalytic activity for oxygen reduction reaction

Nd0.8Sr1.2CoO4±δ(NSC214)/Nd0.5Sr0.5CoO3-δ(NSC113) multilayered heterostructured thin film cathodes of SOFCs exhibit ∼ 20 times difference in polarization resistance and catalytic activity toward oxygen reduction reaction (ORR), which are synthesized by pulsed laser deposition under different temperatures. The thin-films grown at 650 °C possess consistent crystal orientation, while those grown at 500 °C have different crystal orientations between NSC113and NSC214layers. As observed, they show ∼102times and ∼101times, respectively, higher ORR performance than a single-phase NSC113thin-film electrode, as characterized by constructing full cell operated at intermediate-temperature. The origin of such performance differences is analyzed on the basis of crystal orientation by HRXRD, HRTEM, HAADF-STEM, TOF-SIMS, and DFT calculation, and the results indicate that the increased crystal orientations can significantly weaken the positive effects of heterointerface. This observation is attributed to the formation of excessive grain boundaries, which leads to increased formation energy of oxygen vacancy and limited oxygen transportation. These results highlight that the precise control of crystal orientation can make full use of heterostructure to enhance the ORR performance of electrochemical devices.