Competing Magnetic Anisotropy and Domain-Wall Density for Optimizing Magnetization-Induced Water-Oxidation Enhancement

The application of a magnetic field has emerged as an effective method for studying the spin-related effects in the oxygen evolution reaction (OER). However, the presence of spin-unrelated effects under a magnetic field also contributes to the observed OER increment, complicating the identification of spin-related enhancement. This is primarily associated with the intrinsic limitation of the conventional magnetic catalysts that require the continuous application of an external magnetic field to maintain the magnetization. Here, we have developed magnetron-sputtered Co/PtCo multilayer catalysts with perpendicular magnetic anisotropy, enabling a stable magnetization state without continuous magnetic fields. The magnetic anisotropy of the multilayers is controlled through the number of repetitions of Co/PtCo bilayers. As the bilayer number increases from 2 to 25, the domain size at the demagnetized state gradually reduces to the nanometer scale due to the enhanced magnetostatic energy. Upon premagnetization with out-of-plane magnetic fields, the pure spin-enhanced OER is numerically correlated to the change in domain wall ratios, where the global non-spin-related enhancement is effectively excluded. Such spin-enhanced OER is found to be favored by magnetic anisotropy due to the higher magnetic stability to maintain the magnetization state. This Letter provides a new strategy for achieving stable spin-related OER enhancement by magnetic anisotropy, advancing magnetic-field-free spin electrocatalysts to optimize OER performance.