Current Density Calculations of an Octahedral Fe Nanocluster for Selective Electrocatalytic for Nitrogen Reduction

In this work, an octahedral-shaped iron nanocluster (NC) electrocatalyst has been modeled to examine the pathways of electrochemical nitrogen reduction reaction (NRR) and analyze the catalytic activity over the (110) surface. The Heyrovsky-type associative and dissociative NRR mechanisms on the (110) facet and edge of the NC are systematically elucidated by calculating reaction free energies for all the possible elementary reaction steps in NRR. Our results show that the most of the NRR intermediates (*N-2, *N2H, *N2H2, *N, *NH, *NH2, and *NH3) bind weakly on different sites of the NC in comparison to that on the periodic Fe(110) surface. Importantly, the reaction free energy change for the potential determining step (PDS) in the distal associative mechanism with the formation of *NNH on the NC facet is lower than the edge of NC and periodic Fe(110) surface. Our study also indicates that the PDS (*NH2 formation) associated with the periodic Fe(110) surface is no longer the same as the reaction is catalyzed by the NC. The calculated value of working potential is observed lower for Fe-85 NC in comparison to that of the periodic Fe(110) surface. Furthermore, the current density plot indicates that the NC shows less hydrogen evolution reaction (HER) activity compared to other considered Fe based systems. Apart from the working potential study, the positive shift of dissolution potential has also been considered for dissolution behavior of Fe from the NC with respect to surface, confirming its stability in an electrochemical environment. The Fe-85 NC electrocatalyst possess quite a low overpotential of 0.29 V for NRR with reduced HER activity, which is further lower compared to that of the well-established Re(111) and enhanced stability toward Fe dissolution in comparison to that of the periodic Fe(110) surface. Therefore, such an NC system may perform as an efficient catalyst for an electrochemical NRR.