Local Magnetic Effect-Induced Electron Configuration Regulation: Spin Flipping of Iron Centers for Molecular Catalysis

Abstract

Efficient oxygen reduction reactions (ORRs) rely on the appropriate chemical adsorption of triplet oxygen (O 2 ) 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 TiO 2 nanotubes (FePc@TiO 2 ). The inherent magnetic field of these TiO 2 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 O 2 to promote efficient ORR. Compared with the half-wave potential of the original FePc molecule, the halfwave potential of FePc@TiO 2 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 O 2 , providing a strategy for the rational design of spin-based catalysts in oxygen-involved reactions for energy conversion devices.