Bioinspired Molecular Magnetic Field-Responsive Catalyst for On-Demand Switching of 2e− and 4e− Oxygen Reduction

Abstract

Abstract Achieving precise and on-demand steering of the oxygen reduction reaction (ORR) pathway between the efficient 4e − route to H 2 O and the valuable 2e − route to H 2 O 2 remains a pivotal challenge in electrocatalysis. Herein, we address this challenge by designing a bioinspired molecular magnetic field-responsive catalyst (MMFR-C) via magnetic single-atom-anchored Salen-based covalent organic frameworks (MSA-Salen COFs) onto magnetic nanoparticles (single/multi-domain Fe 3 O 4 ). Mimicking cytochrome c oxidase, the MMFR-C employs MSA-Salen COFs as an ordered proton-transfer channel and well-defined N 2 -M-O 2 moieties as enzymatic O 2 activation sites, with Fe 3 O 4 providing a built-in magnetic field for remote regulation of the active-site electronic structure. The bioinspired MMFR-C exhibits switchable ORR pathways. Relative to the pristine Co-Salen COF (26% H 2 O 2 selectivity, n = 3.48), the MMFR-C integrated with a single-domain Fe 3 O 4 exhibits a remarkably enhanced H 2 O 2 selectivity of 63.9% ( n = 2.72), while that with a multi-domain Fe 3 O 4 diverts the ORR pathway toward the 4e − route ( n = 3.67). (i) We elucidate that the uniform magnetic field from the single-domain Fe 3 O 4 in MMFR-C favors orbital hybridization between its active N 2 -M-O 2 moieties and the *OOH intermediate, with moderate *OOH adsorption suppressing O–O scission and thus steering ORR selectivity toward H 2 O 2 . (ii) In contrast, the enhanced specific magnetism from its multi-domain Fe 3 O 4 core optimizes the d -band center of MMFR-C’s active sites, stabilizes triplet O 2 adsorption, and reduces spin-forbidden transition barriers, thereby facilitating O–O cleavage and diverting its ORR pathway to the 4e − route.