Controlled Asymmetric Charge Distribution of Active Centers in Conjugated Polymers for Oxygen Reduction.

Active center reconstruction is essential for searching high performance oxygen reduction reaction (ORR) electrocatalysts. Usually, the ORR activity stems from the special electronic environment of active sites through charge redistribution. In this work, we introduce "asymmetry" strategy to adjust the charge distribution of active centers by precisely designing conjugated polymer (CP) catalysts with different degrees of asymmetry. We synthesized asymmetric backbone CP ( asy-PB ) by modifying boron-nitrogen coordination bonds (B←N) and asymmetric sidechain CP ( asy-PB-A ) with different alkyl chain lengths. As a result, both CPs with backbone and sidechain asymmetry exhibit superior ORR performance to their symmetric counterparts ( sy-P and sy-PB ). Interestingly, asy-PB with greater asymmetry degree shows higher catalytic activity than asy-PB-A with relatively smaller asymmetry. Density functional theory calculations reveal that the increased dipole moment and non-uniform charge distribution caused by asymmetric structure endows the center carbon atom of bipyridine with efficient catalytic activity. These findings provide a mechanistic understanding of asymmetric ORR active structures and this approach gives a new strategy to design high-performance non-metal electrocatalysts.