Fe-Porphyrin MOF with Intrinsic Unsaturated Coordination Metal Sites for Electrocatalytic Nitrogen Reduction

Electrocatalytic nitrogen reduction reaction (eNRR) is expected to overcome the limitations of high temperature, high pressure, and high energy consumption associated with ammonia synthesis in the traditional Haber-Bosch method. It is considered to be a promising approach for ammonia synthesis. In this work, a new Fe-porphyrin metal-organic framework (MOF), with porphyrin derivatives as ligands and Fe atoms as coordination metals, was synthesized as an eNRR catalyst using a simple one-step hydrothermal method. The pyridine N in the porphyrin derivative forms a coordination bond with the Fe atom coordinated inside the porphyrin ligand, resulting in a unique crystal structure that creates an unsaturated five-coordinate environment for the Fe atom. This not only increases the dispersion of Fe atoms but also enhances the adsorption capacity of the Fe atom active center for nitrogen. As a result, good catalytic activity was obtained in neutral electrolyte under ambient conditions, achieving an NH₃ yield of 17.77 μg h^-1 mg_cat.^-1 at -0.2 V versus the reversible hydrogen electrode (RHE). The configuration of unsaturated coordination metal sites within MOFs offers valuable perspectives for the modulation of N adsorption sites and the systematic design of advanced electrocatalysts for NRR.