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

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-N-4 and metal-N-2) 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-N-4 sites in the frameworks, and both M-N-4 and M-N-2 sites contributed to the OER. This work gives us a new platform to construct bifunctional catalysts.