Layered Antiferromagnetic Ordering in the Most Active Perovskite Catalysts for the Oxygen Evolution Reaction

Abstract

We have performed an in‐depth ab initio study of the magnetic structure within the most active perovskites for the oxygen evolution reaction. In all cases, the ground state exhibits an extended antiferromagnetic coupling in the unit cell. Layered antiparallel alignment of the magnetic moments appears to be related to their electrocatalytic activity. All the perovskites calculated within this paper show space‐separated charge‐transport channels depending on the spin orientation. Comparing the electronic structures with the reported activities, we find a direct correlation between the magnetic accumulation on the spin channels in the bulk material and the catalytic activity. We discuss the possible implications of such observations in terms of magnetic interactions. During oxygen evolution in water electrolysis, reactants and products do not preserve spin. For triplet state oxygen to evolve, the catalyst at the anode can speed up the reaction if it is able to balance the magnetism of the oxygen molecule by extracting electrons with an opposite magnetic moment, conserving the overall spin.

Oxygen Evolution Reaction on Perovskite Electrocatalysts with Localized Spins and Orbital Rotation Symmetry

“…The introduction of La 3+ ions into LCF changes the oxidation states of both the Cu and the Fe to 3+, which changes the entire electronic and magnetic structure. LCF is a type G antiferromagnetic insulator bellow 400 K (Figure f), which is indicative of its poor OER activity …”

“…We have adjusted our previous approach, and we now intend to use Δ μ ave as the descriptor of the OER activity. Δ μ ave is calculated as the maximum variation of μ ave (NUPD can be positive or negative) between the accessible orbital orderings under the working conditions.…”

“…The Δ μ ave value of SFCM is predicted to be ∼3.75 μ B [(number of spin‐up electrons−number of spin‐down electrons)/8 B metal atoms×2]. The reported onset potential for the OER for a variety of electro‐catalysts versus Δ μ ave is plotted in Figure . This shows a linear relationship between the OER activity of a perovskite and Δ μ ave , which shows that the Δ μ ave descriptor has the capacity to predict OER effectiveness.…”

“…However, we believe that the efficiency of the most active OER perovskites can also be linked to the magnetic moment of the transition metals if the spin polarisation guarantees remarkable charge transport. Previously, we proposed that, at the atomic scale, local charge and spin conduction channels allow the magnetic selection of the electrons that favours the formation of triplet O 2 . BSCF and CCF are both in a paramagnetic state at 300 K and present complex electronic behaviour with temperature .…”

“…In this study, we explore the exchange interactions behind our initial observations that localised inner spins in the catalyst influence the OER activity . We consider that competing electronic states and orbital dynamism in transition metals in a high(intermediate)‐spin configuration assist the OER.…”