Multi‐Domain versus Single‐Domain: A Magnetic Field is Not a Must for Promoting Spin‐Polarized Water Oxidation

Abstract The reaction kinetics of spin‐polarized oxygen evolution reaction (OER) can be enhanced by ferromagnetic (FM) catalysts under an external magnetic field. However, applying a magnetic field necessitates additional energy consumption and creates design difficulties for OER. Herein, we demonstrate that a single‐domain FM catalyst without external magnetic fields exhibits a similar OER increment to its magnetized multi‐domain one. The evidence is given by comparing the pH‐dependent increment of OER on multi‐ and single‐domain FM catalysts with or without a magnetic field. The intrinsic activity of a single‐domain catalyst is higher than that of a multi‐domain counterpart. The latter can be promoted to approach the former by the magnetization effect. Reducing the FM catalyst size into the single‐domain region, the spin‐polarized OER performance can be achieved without a magnetic field, illustrating an external magnetic field is not a requirement to reap the benefits of magnetic catalysts.