Spin-Promotion Effect to Oxygen Evolution Reaction

ConspectusThe spin-promotion effect in the oxygen evolution reaction (OER) in ferromagnetic (FM) materials has recently received increasing interest. However, the mechanistic picture has not been clarified. Here, we present a comprehensive overview of the mechanisms behind the spin-promotion effect in the OER, bridging the atomic-scale spin interaction with the macroscopic role of the magnetic domains. As a conclusion, FM catalysts have a spin-promotion effect on the OER at a high pH electrolyte. The high pH enables the formation of M-O• oxyl radicals through surface deprotonation. The spins of the single electrons on two neighboring M-O• oxyl radicals are aligned on a magnetic domain but not aligned on a magnetic domain wall. Thus, the triplet O₂ formation is faster on a magnetic domain than on a domain wall. Magnetization leads to converting domain-wall regions to domain ones, and thus the promotion effect can be observed. Such an increment is determined by the domain structure of the magnetic catalysts, i.e., nonsignificant domain wall occupation cannot lead to a remarkable increment by spin-promotion effect. However, one should be reminded that any catalysts can give remarkable increments at a high current density when applied with an external magnetic field, which is due to the promoted bubble removal.