(509cz) Deconvoluting XPS Spectra in Lanthanum-Based Perovskites: An Analysis from First Principles

CO₂ and H₂O co-electrolysis has the potential to create a new source of syngas using solid oxide electrolysis cells (SOECs). Perovskites are promising SOEC cathode materials due to their ability to reduce stable molecules, such as CO₂. The application of these materials in reduction reactions is limited by the lack of understanding of the underlying mechanisms. In this first principles-based Density Functional Theory (DFT) study, we aim to deepen the understanding of the perovskite surface structures and how they impact reactivity by deconvoluting experimental X-ray photoelectron spectroscopy. We hypothesize that the core level binding energy shifts (CLBES) can be accurately obtained within GGA. To validate our functional choice, we will also test two other functionals: SCAN and DFT+U. We model surface impurities to capture features of the surface by calculating the CLBES and deconvolute experimental XPS spectra of three La-based perovskite surfaces with different B-site cations (Ni, Fe and Co).

Our preliminary results on a LaNiO₃(001) NiO₂-terminated surface demonstrate that a generalized gradient functional is sufficiently accurate to capture the CLBES as shown for O 1s in Figure 1. The calculations were performed in a p(2x2) unit cell to model the antiferromagnetic ground state of our systems. We find that the adsorbed oxygen species have higher core level binding energy values as compared to the surface lattice oxygen. We further find that the lattice oxygen in the subsurface layers also have higher CLBES as compared to those at the surface. These results are consistent with our corresponding experimental temperature dependent XPS results. Similar comparisons will be presented for the LaBO₃(001) BO₂-terminated surfaces (B=Co, Fe) with the presence of surface impurities. Once we define our systems at ground state, we will begin investigating the effects of electric fields on the CLBES to better model the electrocatalyst under operating conditions.