Molecular Engineering of Zr–MOFs with Hemin Molecules and Diacetylene Linkages along the Topological Structure for the Tandem Catalysis of Nitrate to Ammonia

A tandem electrocatalyst with dual-active-sites is anticipated to organize the coupling reaction between various intermediates from nitrate to ammonia. Herein, by engineering the metal nodes and ligands of Zr-based metal–organic frameworks (Zr-MOFs) with Fe-porphyrins (Hemins) and diacetylene linkages, respectively, a tandem catalyst of diacetylene-linked Zr–MOFs anchored Hemins has been achieved. The key point here is that the diacetylene linkages could serve as cofactors of Hemins to manage the nitrate to ammonia process via NO₂⁻ intermediates. In addition, the ultrathin Zr–MOFs nanosheet with a well-defined open framework allows it to organize the shuttle diffusion and coupling reaction of various reactants between Hemins and diacetylene linkages in its deep interior. In detail, the NO₂⁻ desorbed from the Hemins could diffuse onto the diacetylene linkages to finish the following hydrogenation process to NH₃. Therefore, such an ultrathin hybrid of diacetylene-linked Zr–MOF@Hemin achieves a Faradaic efficiency of 95.6% with an ammonia yield of 240.9 µmol h⁻¹ cm⁻² at −0.5 V versus RHE. This work indicates the activity of diacetylene linkage in catalysis independent of graphdiyne-based 2D structures by organizing it into the topological structure of Zr–MOFs, which expands the scope of graphdiyne in structure.