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Efficient oxygen reduction reactions (ORRs) rely on the appropriate chemical adsorption of triplet oxygen (O2) on the surface of the catalyst and rapid conversion to doublet intermediate species, accelerating the ORR process. However, overcoming the energy barrier of this spin-forbidden transition via spin coupling with a catalyst remains a major challenge. Herein, iron phthalocyanine (FePc) was attached to the intrinsic atomic step sites on semiconductor TiO2 nanotubes (FePc@TiO2). The inherent magnetic field of these TiO2 atomic step sites induced a spin flip within the Fe 3d near the Fermi level, resulting in enhanced Fe–O covalent bonding as a result of the spin-antiparallel alignment of the electrons in the Fe 3d and the electrons in the π antibonding orbital of the key oxygen intermediate. This process effectively accelerated the protonation step from *OO to *OOH and activated adsorbed O2 to promote efficient ORR. Compared with the half-wave potential of the original FePc molecule, the half-wave potential of FePc@TiO2 greatly increased by 67 mV, up to 0.921 V in 0.1 M KOH. We confirm that the magnetic flipping of single-molecule magnet catalysts is an effective approach for reducing the spin activation barrier of O2, providing a strategy for the rational design of spin-based catalysts in oxygen-involved reactions for energy conversion devices.
Yu et al. (Tue,) studied this question.