A 3D Covalent Organic Framework with In-situ Formed Pd Nanoparticles for Efficient Electrochemical Oxygen Reduction.

Non-platinum noble metals are highly desirable for the development of highly active, stable oxygen reduction reaction (ORR) electrocatalysts for fuel cells and metal-air batteries. However, how to improve the utilization of non-platinum noble metals is an urgent issue. Herein, a highly efficient catalyst for ORR was prepared through homogeneous loading of Pd precursors by a domain-limited method in a three-dimensional covalent organic framework (COF) followed by pyrolysis. The morphology of the Pd nanoparticles (Pd NPs) was well maintained after carbonization, which was attributed to the rigid structure of the 3D COF. Thanks to the uniform distribution of Pd NPs in the carbon, the catalyst exhibited a remarkable half-wave potential of 0.906 V and a Tafel slope of 70 mV dec-1 in 0.1 M KOH, surpassing the commercial Pt/C catalyst (0.863 V and 75 mV dec-1). Furthermore, a maximum power density of 144.0 mW cm-2 was achieved at 252 mA cm-2, which was significantly higher than the control battery (105.1 mW cm-2). This work not only provides a simple strategy for in-situ preparation of highly dispersible metal catalysts in COFs, but also offers new insights into the ORR electrocatalysis.