Morphology-Dependent Enhancement of Electrocatalytic Nitrogen Reduction Activity Using Iron Phthalocyanine Nanostructures

Abstract

Ammonia is one of the most essential raw materials for daily life applications. As an alternative to the Haber–Bosch process, scientists are focusing on an important domain of electrocatalysis for ammonia production. Herein, we approached a morphological adaptation of the electrocatalyst (iron phthalocyanine, FePc) based on hollow nanotube and rod types; the catalyst showed different N₂-to-NH₃ productivity. Under ambient conditions, FePc nanorods showed a good ammonia yield rate and Faradaic efficiency (FE) of 323.44 μg h^–1 mg_cat.^–1 and 23.33%, respectively, at −0.4 V vs RHE in 0.05 M H₂SO₄. However, when the rod was adapted to a hollow nanotube structure by control of the temperature and time parameters, the ammonia productivity further improved. Under the same conditions, FePc nanotubes showed an excellent ammonia yield rate of 425.46 μg h^–1 mg_cat.^–1 and a corresponding FE of 23.61% at −0.4 V vs RHE. In addition to experimental observations, theoretical analysis using density functional theory is also provided to establish the reaction mechanism of ammonia synthesis from nitrogen reduction reaction (NRR) using an FePc electrocatalyst. This work opens an avenue showing geometric structural induction of electrocatalytic activity toward future sustainable ammonia production.