Oxygen Reduction Reaction and Electronic Properties of LnO-Terminated Surfaces of Pr₂NiO₄and La₂NiO₄

Density functional theory calculations were performed to elucidate the origin of catalytic activity of the pristine LnO-terminated surfaces of two Ruddlesden-Popper phase oxides of industrial interest. The direct comparison of molecular oxygen interaction with La₂NiO₄and Pr₂NiO₄allowed us to evaluate the electronic effect on the oxygen reduction reaction energetics. We have further addressed the surface catalytic activity as a function of interstitial oxygen occupancy in the rock salt layer and provided a possible explanation for the limits of the interstitial oxygen concentration. The oxide ion transport in the rock salt layer was compared for La₂NiO_4.125and Pr₂NiO_4.125. The diffusion difference was attributed to the electronic structure of the valence shells of Pr and La. The different polarizability of those elements would lead to the opposite effect on the transition state stability. In-depth understanding of the La₂NiO₄and Pr₂NiO₄(including La₂NiO_4.125and Pr₂NiO_4.125) electronic properties allowed us to refer electronic and hole conductivities to the computed band gaps and the electronic structure of the valence bands. Our study shows that while La₂NiO₄and Pr₂NiO₄share a similar crystallographic structure, the most important properties, such as surface catalytic activity, ionic diffusivity, and electron transport, are a direct consequence of the valence shell structure of the Ln cations: La and Pr.