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 O-2 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 O-2 adsorbed onto the perfect and defective La2NiO4 (100) surface to elucidate the interaction mechanism between O-2 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 O-2 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 O-2 molecule on the La2NiO4 (100) surface; in addition, oxygen vacancy can be an active site in O-2 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.