The Effects of Ligands with Different Electron Donation on the Nitrogen Reduction Performance of Constructed Co-MOFs: NH or NH?

Four cobalt-based metal-organic frameworks (Co-MOFs) based on different ligands with varying electron-donating properties (dpt = 2,5-di(pyridin-4-yl)-1,3,4-thiadiazole, NH₂bdc = 5-aminoisophthalic acid, OHbdc = 5-hydroxyisophthalic acid, H₂tdc = thiophene-2,5-dicarboxylic acid, and hfipbb = 4,4'-(hexafluoropropane-2,2-diyl)bisbenzoic acid) are synthesized. Among them, Co-dpt-NH₂bdc demonstrates the highest nitrogen reduction reaction activity, achieving an ammonia (NH) yield of 68.61 µg·h⁻¹·mg⁻¹ and Faraday efficiency (FE) of 6.75 %. The enhanced performance is attributed to stronger electronic interactions and improved charge transfer capabilities facilitated by the electron-donating properties of NH₂bdc. Additionally, Co-dpt-NH₂bdc can produce hydrazine (N₂H₄), achieving N₂H₄ yield of 90.62 µg·h⁻¹·mg⁻¹ and FE of 65.67 %, as a byproduct caused from the interaction between the generated NH₃ and the amino group on the NH₂bdc ligand. This work highlights the potential of molecular engineering in tuning the electronic states of catalytic sites to enhance electrocatalytic activity and provides insights into the production of N₂H₄ through ligand modulation.