Interaction of La₂NiO₄ (100) surface with oxygen molecule: A first-principles study

Along the way to designing of new cathode materials for solid oxide fuel cells (SOFCs), an understanding of the mechanism of oxygen reduction reaction (ORR) plays a key role, especially the interaction between O₂ molecule and surface of cathode. Recently, La₂NiO₄ with K₂NiF₄-type structure has been developed, and it has received great attention as an oxygen sensor and a potential cathode for SOFCs. However, the chemical activity of La₂NiO₄, in particular, the ORR on the surface, has not been studied so thoroughly. In this report, we present the structural and energetic results of O₂ adsorbed onto the perfect and defective La₂NiO₄ (100) surface to elucidate the interaction mechanism between O₂ molecule and cathode using atomistic computer simulation based on density functional theory. The results show that the surface structure and the adsorbed configurations are vital for O₂ adsorption. and activation. The adsorbed species on the perfect surface are energetically less favorable than defective surface. The Ni site is preferred with adsorption energy of -1.25 (Ni-super) and -1.80 eV (Ni-per), much higher than these of La site, supporting the fact that transition-metal cations are more active than lanthanon metals in K₂NiF₄-type compounds. Surface oxygen vacancy is found to enhance the adsorption energy of O₂ molecule on the La₂NiO₄ (100) surface; in addition, oxygen vacancy can be an active site in O₂ adsorption. The most stable configuration is Ni-O-Ni mode, with the highest adsorption energy being -2.61 eV. This can be confirmed by the analysis of the local density of states (LDOS) and the difference electron density. These results have an important implication for understanding the ORR on La₂NiO₄ (100) surface.