Coordination Engineering of Iron-Polyphthalocyanines with H-Substituted Graphdiyne for the Tandem Catalysis of Nitrate to Hydroxylamine

Hydroxylamine (NH₂OH) can be generated by controlling the nitrate electroreduction process, the key of which lies in the hydrogenation of *NO. In this study, hydrogen-substituted graphdiyne (HsGDY) is developed to engineer the growth of iron-polyphthalocyanine (FePPc) with four Fe-N₄ centers around the diacetylene linkages via d–π interactions, where numerous isolated electrochemical interfaces with high degrees of site exposure are achieved. Density functional theory results indicate electron transfer from Fe-N₄ sites to diacetylene linkages, which prevents the hydrogenation of *NH₂OH. In such a hybrid, a relay process occurs between HsGDY and FePPc, where the diacetylene linkages work as the transfer stations of NO₃⁻ to NO₂⁻, whereas the isolated Fe-N₄ sites further help manage NO₂⁻ to NH₂OH. In addition, the well-aligned nanoarrays along with the extended conjugated structure of HsGDY make it effective in directing both electron and mass transfer around FePPc. Thus, HsGDY@FePPc achieves a NH₂OH yield rate of 52.3 µmol h⁻¹ cm⁻² with a Faradic efficiency (FE) of 34.0% at − 0.7 V vs RHE. When further applied in the electrosynthesis of cyclohexanone oxime, a FE of 51.0% is achieved. This work reports a coordination method for engineering both the structure and performance of a molecular catalyst via the diacetylene linkages of HsGDY.