Synthesis of Shape-Controlled Layered Lanthanum Nickelate Oxides with Enhanced Oxygen Exchange Properties

Mixed ionic and electronic conducting metal oxides play an important role in many technologically relevant electrochemical energy conversion and storage processes. Lanthanum nickelate oxides are among these mixed conducting oxides that exhibit very high oxygen exchange and transport rates. These materials are characterized by a layered structure of alternating perovskite and rock-salt layers and are generally expressed with the formula, A₂BO_4+δ. In this structure δ represents the oxygen hyperstoichiometry, which is thought to contribute to fast oxygen transport rates in these materials ^[1-4]. We have recently shown that the surface structure of these oxides plays an important role in their surface oxygen exchange and reduction properties. Lanthanum nickelates with nanorod structure highly terminated by (001) NiO surface facets exhibit higher oxygen exchange rates as compared to traditional spherical structure lanthanum nickelate oxides^{[1, 2]}. In this contribution we show that the nanorod-structured lanthanum nickelates can be obtained in a controlled way using a reserve microemulsion synthesis approach. We also demonstrate how this approach is robust in synthesizing structure-controlled lanthanum nickelate of various compositions. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies are used to characterize the crystalline structures and morphologies of these oxides.

References

[1] Ma X, Wang B, Xhafa E, et al. Synthesis of shape-controlled La₂NiO_4+δ nanostructures and their anisotropic properties for oxygen diffusion[J]. Chemical Communications, 2015, 51(1): 137-140.

[2] Ma X, Carneiro J, Gu X K, et al. Engineering complex, layered metal oxides: High performance nickelate oxide nanostructures for oxygen exchange and reduction[J]. ACS Catalysis, 2015.

[3] Zhu J, Li H, Zhong L, et al. Perovskite Oxides: Preparation, Characterizations, and Applications in Heterogeneous Catalysis[J]. ACS Catalysis, 2014, 4(9): 2917-2940.                                                    

[4] Chroneos A, Vovk R V, Goulatis I L, et al. Oxygen transport in perovskite and related oxides: A brief review[J]. Journal of Alloys and Compounds, 2010, 494(1): 190-195.