Ferromagnetic ligand holes in cobalt perovskite electrocatalysts as an essential factor for high activity towards oxygen evolution

Abstract

The definition of the interplay between chemical composition, electro-magnetic configuration and catalytic activity requires a rational study of the orbital physics behind active materials. Apart from Coulomb forces, quantum spin exchange interactions (QSEI) are part of the potentials that differentiate the activity of magnetic oxides, strongly correlated electrocatalysts, in electron transfer reactions. Ferromagnetic (FM) cobalt oxides can show low overpotentials for the oxygen evolution reaction (OER) and the La_1−XSr_XCoO_3−δ (0 ≤ X ≤ 1) family of perovskites is good ground to gain understanding of the electronic interactions in strongly correlated catalysts. In this case, Sr-doping raises the OER activity and the conductivity and increases FM spin moments. The efficiency of electrocatalysts based on Earth-abundant 3d-transition metals correlates with the interrelated factors: mild-bonding energies, the reduction of the electronic repulsions because of the QSEI in the open-shells, and enhanced spin delocalization in FM ordering. The reason for the outstanding OER activity of SrCoO_3−δ is the accumulation of FM holes in the 3d–2p bonds, including the ligand orbitals, thus facilitating spin-selected charge transport and production of triplet O₂ moieties from the oxidation of diamagnetic precursors. Spin-polarized oxygen atoms in the lattice can participate in O–O coupling and release of O₂ in a Mars–Van Krevelen mechanistic fashion. We show that the stabilizing FM QSEI decrease the adsorption and activation energies during oxygen evolution and spin-dependent potentials are one of the factors that govern the catalytic activity of magnetic compositions: spintro-catalysis.