Metal-porphyrin-based three-dimensional covalent organic frameworks for electrocatalytic nitrogen reduction

Electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions presents a sustainable method for renewable ammonia production. However, the development of high-performance NRR electrocatalysts with satisfactory efficiency and selectivity remains a significant challenge. Herein, we design and synthesize two metal-porphyrin based 3D COFs bearing metal-N4 catalytic sites with different 3D spatial arrangements (scu and flu topologies) for this purpose. The anchoring of metal ions (Fe, Cu) at the center of the planar conjugated-porphyrin ring enhances the activity and selectivity of electrocatalytic NRR. Significantly, the 3D COFs with Fe-N4 catalytic sites feature higher NH3 yield and Faradaic efficiency (94.26 ± 4.9 μg h-1 mg-1 and 18.37 ± 0.96 % at −0.5 V vs RHE, reversible hydrogen electrode) than those with Cu-N4 centers, making them promising candidates for NRR electrocatalysts. This work not only enriches the topological library of 3D COFs, but also provides an idea for the rational design of metal porphyrin-based COFs for NH3 production.