Instability of PCN-224(Fe) during the oxygen reduction reaction; metal-organic framework electrocatalysts may have an Achilles heel.

Incorporation of catalytic sites within metal-organic frameworks has been considered advantageous as the amount of catalytic sites per cm2 electrode surface and be greatly expanded, while simultaneously the stability of the catalytic sties can be greatly improved. In contrast to previous studies, it is found that the dPCN-224(Fe) catalyst is extremely sensitive towards reactive oxygen species (ROS) formation during the electrochemical oxygen reduction reaction and deactivates within seconds. Very little is known about deactivation of catalytic sites in MOFs and what the effect could be on the overall catalytic performance of the MOF as a function of time. Herein, the degradation mechanism of dPCN-224(Fe) with ROS is studied in detail and it is shown that a few catalytic sites - presumably positioned at the interface between the MOF and the carbon support - are the specific sites targeted by ROS leading to the complete breakdown of all activity. Therefore, even though the density of active sites is exceptionally high in MOF systems, the catalytic reaction is strongly dependent on only few active sites that are directly positioned at the connection between the MOF and the carbon electrode or support.