Metal organic polymers with dual catalytic sites for oxygen reduction and oxygen evolution reactions

Abstract

Metal–organic frameworks and covalent organic frameworks have been widely employed in electrochemical catalysis owing to their designable skeletons, controllable porosities, and well-defined catalytic centers. However, the poor chemical stability and low electron conductivity limited their activity, and single-functional sites in these frameworks hindered them to show multifunctional roles in catalytic systems. Herein, we have constructed novel metal organic polymers (Co-HAT-CN and Ni-HAT-CN) with dual catalytic centers (metal–N4 and metal–N2) to catalyze oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). By using different metal centers, the catalytic activity and selectivity were well-tuned. Among them, Co-HAT-CN catalyzed the ORR in a 4e− pathway, with a half-wave potential of 0.8 V versus RHE, while the Ni-HAT-CN catalyze ORR in a 2e− pathway with H2O2 selectivity over 90%. Moreover, the Co-HAT-CN delivered an overpotential of 350 mV at 10 mA cm−2 with a corresponding Tafel slope of 24 mV dec−1 for OER in a 1.0 M KOH aqueous solution. The experimental results revealed that the activities toward ORR were due to the M–N4 sites in the frameworks, and both M–N4 and M–N2 sites contributed to the OER. This work gives us a new platform to construct bifunctional catalysts.