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 , *N 2 H, *N 2 H 2 , *N, *NH, *NH 2 , and *NH 3 ) 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 (*NH 2 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.

The design and development of highly efficient catalysts for the electrochemical reduction of nitrogen into NH 3 at ambient temperature and pressure has been an area of major research interest. In this work, electrochemical N 2 reduction following Heyrovsky-type associative and dissociative mechanisms is studied on the periodic Fe(111) surface using density functional theory calculations. Interestingly, the associative pathway has not been investigated on the Fe(111) surface in any of the previous studies though it is reported to be one of the best catalysts for ammonia synthesis. Therefore, we have investigated both the nitrogen reduction reaction (NRR) mechanisms on the Fe(111) surface. Free-energy analysis of associative and dissociative reaction pathways has been carried out, and it has been found that the associative mechanism is favorable over the dissociative mechanism with the formation of *NH 2 NH 2 as a potential-determining step. Furthermore, the catalytic activity of cuboctahedral iron nanoclusters (NCs) is also investigated to understand the dimensional dependence of the Fe-based NRR activity. The NC shows a higher NRR activity by following an energetically more favorable ammonia desorption compared to the Fe(111) surface. The observed activity trends are explained from the site-specific interaction and binding energy of reaction intermediates. The surpassing of the high energy-demanding N 2 dissociation step by both the catalytic systems implies that NRR can be facilitated in an energetically favorable manner via an electrochemical reduction pathway.

Large-scale ammonia production through sustainable strategies from naturally abundant N 2 under ambient conditions represents a major challenge from a future perspective. Ammonia is one of the promising carbon-free alternative energy carriers. The high energy required for NN bond dissociation during the Haber-Bosch process demands extreme reaction conditions. This problem could be circumvented by tuning Fe catalyst composition with the help of an induced ligand effect on the surface. In this work, we utilized density functional theory calculations on the Fe(110) surface alloyed with first-row transition-metal (TM) series (Fe−TM) to understand the catalytic activity that facilitates the electrochemical nitrogen reduction reaction (NRR). We also calculated the selectivity against the competitive hydrogen evolution reaction (HER) under electrochemical conditions. The calculated results are compared with those from earlier reports on the periodic Fe(110) and Fe( 111) surfaces, and also on the (110) surface of the Fe 85 nanocluster. Surface alloying with late TMs (Co, Ni, Cu) shows an improved NRR activity, whereas the low exchange current density observed for Fe− Co indicates less HER activity among them. Considering various governing factors, Fe-based alloys with Co (Fe−Co) showed enhanced overall performance compared to the periodic surface as well as other pure iron-based structures previously reported. Therefore, the iron-alloy based structured catalysts may also provide more opportunities in the future for enhancing NRR performance via electrochemical reduction pathways.

Ammonia production from the earth-abundant feedstock of N 2 is one of the most attractive fields of research. Searching for an alternative iron-based electrocatalyst for direct ammonia synthesis is a challenging process due to the harsh reaction conditions present in the traditional route of the Haber−Bosch process. In the present work using the density functional theory (DFT) calculations, we have systematically investigated the potential of late transition metal (TM = Co, Ni, and Cu) substitution on the surface, subsurface, and surface + subsurface of Fe(110) toward the nitrogen reduction reaction (NRR) and the hydrogen evolution reaction (HER). We demonstrate that a Ni-substituted surface + subsurface catalyst can favor the electrocatalytic ammonia synthesis with the maximum Faradaic efficiency by suppressing the HER compared to the previously reported catalysts for ammonia production. These findings open a way in terms of designing surface + subsurface-substituted alloy catalysts for various catalytic reactions.

Developing advanced energy storage systems to address the intermittency of renewable energy sources is crucial for meeting the ever-increasing energy demands. Among post lithium-ion battery systems, dual-ion batteries (DIBs) have...