Highly Durable and Selective Fe- and Mo-Based Atomically Dispersed Electrocatalysts for Nitrate Reduction to Ammonia via Distinct and Synergized NO₂^– Pathways

Abstract

Aimed toward the pursuit of manufacturing ammonia in a carbon-neutral and decentralized manner, the electrocatalytic nitrate reduction reaction (NO3RR) not only promises an effective route for carbon-neutral ammonia synthesis but also offers potential advantages to wastewater remediation. Here, we describe the efficacy of bioinspired, atomically dispersed catalysts for the NO3RR in aqueous media via a catalytic cascade. Compared to nanoparticles with extended catalytic surfaces, atomically dispersed catalysts are largely underexplored in this field, despite their intrinsic selectivity toward mono-nitrogen species over their dinitrogen counterparts. Herein, we specifically report on a series of nitrogen-coordinated mono- and bimetallic, atomically dispersed, iron- and molybdenum-based electrocatalysts for ammonia synthesis via the NO3RR. The key role of the *NO2/NO2– intermediates was identified both computationally and experimentally, wherein the Fe–N4 sites and Mo–N4/*O–Mo–N4 sites carried distinct associative and dissociative adsorption of NO3– molecules, respectively. By integrating individual Fe and Mo sites on a single bimetallic catalyst, the unique reaction pathways were synergized, achieving a Faradaic efficiency of 94% toward ammonia. Furthermore, the robustness of the bimetallic FeMo–N–C catalyst was highlighted by five consecutive 12 h electrolysis cycles with the Faradaic efficiency being maintained above 90% over the entire 60 h. The utilization of catalytic cascades, synergizing distinct reaction pathways on heterogeneous single-atom sites, is largely unconstrained by linear scaling relations of reaction intermediates and sheds light on designing electrocatalysts for highly selective, efficient, and durable ammonia synthesis.

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