Fe dominated and O-vac rich mesoporous NiFe2O4 for enhanced electrocatalytic Nitrogen reduction to ammonia through enzymatic pathway

Abstract

Electrocatalytic nitrogen reduction (ENRR) is a green and versatile approach to reduce atmospheric nitrogen into ammonia. This promising approach however lacks inexpensive and efficient electrocatalyst that promotes scalable ammonia production. Herein, we present a non-precious, mesoporous NiFe₂O₄ nanosheets (m-NiFe₂O₄ NS) prepared via a simple solution combustion method for the ENRR. The synthesized m-NiFe₂O₄ NS showed an outstanding NH₃ yield of 45 μgh⁻¹mg_cat^-1, TOF of 0.618h^-1, and Faradaic efficiency of 12 % at a potential of -0.4 V vs. RHE. This activity of m-NiFe₂O₄ NS is attributed to highly porous structure, and the presence of Fe and Ni atoms, where Fe atoms active sites promotes N₂ activation, polarization, and boosts ENRR activity and Ni atoms protects ENRR active sites on Fe for competing HER and makes them exclusively available for ENRR. In this work, we proposed enzymatic pathway mechanism based on in-situ Raman investigations. That revealed the formation of *N₂H and *N₂H₂ type intermediates during ammonia formation. The preliminary step is N₂ adsorption on the active sites (metal centres and surface defects) of m-NiFe₂O₄NS followed by proton coupled electron transfer reactions (PCET) that generates*N₂H and *N₂H₂ type intermediates which then undergoes series of PCETs to generate NH₃.