The Synthesis and Oxygen Transport Properties of La2NiO4 Nanoparticles

This work highlights a novel approach for synthesizing La₂NiO_4+δ nanoparticles with controlled morphology through the use of reverse micro-emulsion systems. La₂NiO_4+δ is a mixed ionic and electronic conducting (MIEC) oxide that exhibits excellent oxygen transport properties due to oxygen hyperstoichiometry in the lattice. The oxygen exchange/transport properties play an important role in the catalytic activity of La₂NiO_4+δ toward reactions involving oxygen. In this contribution, we show that the oxygen exchange properties of these materials can be tuned by controlling the size and shape of the oxide nanoparticles via a reserve micro-emulsion synthesis approach. We show that the ratio of the surfactant (CTAB) to water (W₀) plays a key role in controlling the aspect ratio and the distribution of surface facets of the nanostructures. Variations in W₀ lead to changes in the geometry of the particles from nanorods to polyhedra. In addition, the choice of precipitating agent directly influences the size of nanoparticles. Thermal gravimetric analysis (TGA) of the synthesized La₂NiO_4+δ shows anisotropic behavior of oxygen diffusion, which is directly linked to the degree of oxygen hyperstoichiometry (δ) and distribution of surface facets. This method has provided opportunities for optimizing the morphology of La₂NiO_4+δ nanoparticles, which has implications in catalytic processes that involve redox reactions with oxygen where mixed ionic and electronic conductivity is required.