Switchable 2 e ⁻ /4 e ⁻ ORR Pathway Directed by Spin‐State Engineering for High‐Rate H

ABSTRACT

Precise control of the 2 e ⁻ /4 e ⁻ oxygen reduction reaction (ORR) pathway is essential for directing H ₂ O ₂ production toward high efficiency and scalability. However, rational regulation of the active site's electronic spin‐states to dictate selectivity remains a fundamental challenge. Herein, we report a flexible regulation strategy for tuning the 2 e ⁻ or 4 e ⁻ ORR pathway by precisely engineering the spin‐state and charge density at cobalt (Co) metal centers within metal coordination polymers (MCPs) via ligand functionalization. The d‐π conjugation system of Co‐1,2,4,5‐benzenetetramin with electron‐withdrawing and electron‐donating functional group modifications provides the possibility for electronic delocalization. Interestingly, this modulation effectively adjusts the adsorption affinity and electron transfer characteristics of the key intermediate *OOH. It is found that the increased electron delocalization can reduce the charge density over the high‐spin Co ²⁺ center, assisting 4 e ⁻ ORR ( E _1/2 = 0.86 V vs. RHE). In contrast, the electron‐donating substituents increase the charge density of the Co ²⁺ center, showing a low‐spin‐state, selecting a 2 e ⁻ ORR pathway (H ₂ O ₂ selectivity = 92.7%). The present research provides in‐depth insights into the spintronic understanding and rational design of materials with high selectivity based on electron delocalization.