On the O 2p-band center as a descriptor for the catalytic activity of complex oxides

Electronic descriptors extracted from Density Functional Theory (DFT) calculations are a powerful tool in designing new perovskite-based materials that could catalyze oxygen reduction (ORR) and oxygen evolution (OER) reactions [1]. In particular, a good correlation has been found between the O 2p-band center and the charge transfer energy, the oxygen vacancy formation energy, the adsorption energy, or the overpotential. While such correlations are proven for simple ABO₃ perovskites, there are few studies dealing with oxides presenting high chemical and structural complexity. In this work, the layered perovskite system YSr₂Cu₂FeO_7+δ (YSCFO) [2] is investigated to analyze the effects of oxygen non-stoichiometry and vacancy ordering in the O 2p-band center values. In YSCFO, the formal oxidation states range from Fe⁴⁺ and mixed Cu³⁺/Cu²⁺ (δ =1 ) to Fe³⁺ and Cu²⁺( δ =0 ). To establish a comparison with a single-TM oxide, band centers are also extracted for the Ruddlesden Popper Sr_2-xLa_xFe₂O₄ phase with 0 < x < 2 (formally, from Fe(IV) to Fe(II)).

DFT calculations (SCAN, PBE+U) are performed using the ab initio total energy program (VASP). The O 2p-band centers are extracted from the calculated DOSs. For RP-Sr_2-xLa_xFe₂O₄, the O p-band center displays a linear trend with the Fe oxidation state. In the complex system YSCFO, the interplay between Cu and Fe 3d states breaks the linearity. In addition, for a given oxygen content, the O 2p-band center varies with the oxygen/vacancy ordering in the FeO_1+δ layers. Importantly, the O 2p-band center values calculated for the YSCFO system suggest that these materials may possess electrocatalytic activity, as the obtained values are between -1.0 and -1.8 eV [1].

1. Jacobs, R.; Mayeshiba, T.; Booske, J.; Morgan, D. Advanced Energy Materials 2018, 8, doi:10.1002/aenm.201702708.
2. Gómez-Toledo, M.; López-Paz, S.A.; García-Martín, S.; Arroyo-de Dompablo, M.E. Inorganic Chemistry 2023, doi:10.1021/acs.inorgchem.2c03475.