Low-spin state design of highly active diatomic catalysts for oxygen reduction reaction

Fe-based atomic catalysts are widely considered among the most promising non-noble candidates for the oxygen reduction reaction (ORR). The precise manipulation of spin states directly determines their performance but remains highly challenging. Herein, we demonstrate a source-reduction approach to design a low-spin Fe²⁺/Cu-N-C diatomic catalyst with fully occupied d_z² orbitals. Compared with conventional Fe³⁺ catalysts, the adsorption energy of the *OH intermediate was significantly lowered by minimizing metal-oxygen orbital interactions. In situ synchrotron evidence and ab initio molecular dynamics simulations further reveal the unusually rapid O-O bond cleavage for *OOH dissociation that is viewed as another key rate-limiting ORR step. The catalyst therefore exhibited fast ORR kinetics with remarkably high half-wave potentials of 0.926/0.828 V in alkaline/acidic media and superior durability of only 17 mV loss after 10 000 cycles, along with outstanding fuel cell performance. This work provides new insights into the spin state engineering and reaction pathway modulation of catalysts.