Spin-polarized oxygen evolution reaction under magnetic field

TLDR

The oxygen evolution reaction (OER) is the rate‑limiting step in water splitting, involving four electron transfers that generate triplet O₂ from singlet precursors, and recent work suggests spin selection could accelerate OER but the kinetics remain unclear. This study tests whether ferromagnetic ordered catalysts can serve as spin polarizers under a constant magnetic field to enhance OER. Spin polarization is achieved at the first electron transfer step through coherent spin exchange between the catalyst and adsorbed oxygen, and subsequent electron transfers follow Hund’s rule and Pauli exclusion, ultimately producing triplet O₂. The results confirm that spin‑polarized kinetics occur at the first step, the method is ineffective with non‑ferromagnetic catalysts, and the approach demonstrates a pathway for designing spin‑dependent OER catalysts.

Abstract

Abstract The oxygen evolution reaction (OER) is the bottleneck that limits the energy efficiency of water-splitting. The process involves four electrons’ transfer and the generation of triplet state O 2 from singlet state species (OH - or H 2 O). Recently, explicit spin selection was described as a possible way to promote OER in alkaline conditions, but the specific spin-polarized kinetics remains unclear. Here, we report that by using ferromagnetic ordered catalysts as the spin polarizer for spin selection under a constant magnetic field, the OER can be enhanced. However, it does not applicable to non-ferromagnetic catalysts. We found that the spin polarization occurs at the first electron transfer step in OER, where coherent spin exchange happens between the ferromagnetic catalyst and the adsorbed oxygen species with fast kinetics, under the principle of spin angular momentum conservation. In the next three electron transfer steps, as the adsorbed O species adopt fixed spin direction, the OER electrons need to follow the Hund rule and Pauling exclusion principle, thus to carry out spin polarization spontaneously and finally lead to the generation of triplet state O 2 . Here, we showcase spin-polarized kinetics of oxygen evolution reaction, which gives references in the understanding and design of spin-dependent catalysts.