How the Bioinspired Fe₂Mo₆S₈ Chevrel Breaks Electrocatalytic Nitrogen Reduction Scaling Relations

Abstract

The nitrogen reduction reaction (NRR) is a renewable alternative to the energy-and CO 2 -intensive Haber− Bosch NH 3 synthesis process but is severely limited by the low activity and selectivity of studied electrocatalysts. The Chevrel phase Fe 2 Mo 6 S 8 has a surface Fe−S−Mo coordination environment that mimics the nitrogenase FeMo-cofactor and was recently shown to provide state-of-the-art activity and selectivity for NRR. Here, we elucidate the previously unknown NRR mechanism on Fe 2 Mo 6 S 8 via grand-canonical density functional theory (GC-DFT) that realistically models solvated and biased surfaces. Fe sites of Fe 2 Mo 6 S 8 selectively stabilize the key *NNH intermediate via a narrow band of free-atom-like surface d-states that selectively hybridize with p-states of *NNH, which results in Fe sites breaking NRR scaling relationships. These sharp d-states arise from an Fe−S bond dissociation during N 2 adsorption that mimics the mechanism of the nitrogenase FeMo-cofactor. Furthermore, we developed a new GC-DFT-based approach for calculating transition states as a function of bias (GC-NEB) and applied it to produce a microkinetic model for NRR at Fe 2 Mo 6 S 8 that predicts high activity and selectivity, in close agreement with experiments. Our results suggest new design principles that may identify effective NRR electrocatalysts that minimize the barriers for *N 2 protonation and *NH 3 desorption and that may be broadly applied to the rational discovery of stable, multinary electrocatalysts for other reactions where narrow bands of surface d-states can be tuned to selectively stabilize key reaction intermediates and guide selectivity toward a target product. Furthermore, our results highlight the importance of using GC-DFT and GC-NEB to accurately model electrocatalytic reactions.

The journey of iron-based electrocatalytic materials for nitrogen reduction reaction: from current status to future prospects

“…101,[133][134][135] Theoretical calculations and experimental works proofed that synergy and electron coupling effect between Fe and Mo facilitate the charge transfer from metal orbitals to nitrogen species, and thus weaken the inert nitrogen triple bond. 56,118,136,137 Singstock et al explored how Fe 2 Mo 6 S 8 broke NRR scaling relationships using grand-canonical density functional theory (GC-DFT). 136 According to theoretical predictions, Mo sites exhibited the intrinsic characteristics of strong N 2 adsorption and large NH 3 dissociation barriers, even poisoning due to the over-binding of *NH 3 .…”

“…56,118,136,137 Singstock et al explored how Fe 2 Mo 6 S 8 broke NRR scaling relationships using grand-canonical density functional theory (GC-DFT). 136 According to theoretical predictions, Mo sites exhibited the intrinsic characteristics of strong N 2 adsorption and large NH 3 dissociation barriers, even poisoning due to the over-binding of *NH 3 . Fe active sites with sharp bands of freeatom-like d-states conspicuously overlapped with the nitrogen Fig.…”

“…224 Theoretical calculation: reproduced with permission: copyright 2022, American Chemical Society. 136 atom dispersion, and metal-organic framework precursors design; the related progress will be discussed in this section. 3.3.1.1.…”

Insights from Enzymatic Catalysis: A Path towards Bioinspired High‐Performance Electrocatalysts

“…Mechanistic studies have elucidated that Fe sites of the heterogeneous electrocatalyst selectively stabilize a key intermediate of the catalytic process. [139]…”

Hypotoxic synthesis of Co2P nanodendrites for boosting ammonia electrosynthesis from nitrate

“…Unfortunately, due to the inherent inertia of NRN (bond energy: 941 kJ mol À1 ), limited nitrogen solubility, and the competitive hydrogen evolution reaction (HER) result in the formation rate, selectivity, and Faraday efficiency of nitrogen electroreduction to NH 3 being far from meeting the application requirements. 8,9 By contrast, the electrochemical reduction of nitrate to NH 3 (nitrate reduction reaction, NO 3 À RR, NO 3 À + 6H 2 O + 8e À -NH 3 + 9OH À ) represents an alternative and attractive route for sustainable ambient NH 3 synthesis owing to the high solubility of nitrate in aqueous solutions and the low dissociation energy of NQO (204 kJ mol À1 ). [10][11][12][13][14] Moreover, nitrate contamination has also been linked to increased risk for various types of cancer in humans.…”