Morphology-Dependent\nEnhancement of Electrocatalytic\nNitrogen Reduction Activity Using Iron Phthalocyanine Nanostructures

Ammonia is one of the most essential raw materials for\ndaily life\napplications. As an alternative to the Haber–Bosch process,\nscientists are focusing on an important domain of electrocatalysis\nfor ammonia production. Herein, we approached a morphological adaptation\nof the electrocatalyst (iron phthalocyanine, FePc) based on hollow\nnanotube and rod types; the catalyst showed different N<sub>2</sub>-to-NH<sub>3</sub> productivity. Under ambient conditions, FePc nanorods\nshowed a good ammonia yield rate and Faradaic efficiency (FE) of 323.44\nμg h<sup>–1</sup> mg<sub>cat.</sub><sup>–1</sup> and 23.33%, respectively, at −0.4 V vs RHE in 0.05 M H<sub>2</sub>SO<sub>4</sub>. However, when the rod was adapted to a hollow\nnanotube structure by control of the temperature and time parameters,\nthe ammonia productivity further improved. Under the same conditions,\nFePc nanotubes showed an excellent ammonia yield rate of 425.46 μg\nh<sup>–1</sup> mg<sub>cat.</sub><sup>–1</sup> and a\ncorresponding FE of 23.61% at −0.4 V vs RHE. In addition to\nexperimental observations, theoretical analysis using density functional\ntheory is also provided to establish the reaction mechanism of ammonia\nsynthesis from nitrogen reduction reaction (NRR) using an FePc electrocatalyst.\nThis work opens an avenue showing geometric structural induction of\nelectrocatalytic activity toward future sustainable ammonia production.