A high-performance transition metal single-atom-anchored IrN ₂ monolayer as an electrocatalyst for nitrate reduction to ammonia

The electrocatalytic nitrate reduction reaction (NO₃RR) has emerged as a promising strategy for simultaneous nitrate remediation and sustainable ammonia synthesis. However, the development of electrocatalysts with high activity and selectivity remains a critical challenge. Herein, we systematically investigated 23 transition metal (3d-5d TM) single-atom-anchored IrN₂ monolayers (TM-IrN₂) as potential NO₃RR electrocatalysts using density functional theory calculations. A distinct volcano-type relationship is established between the limiting potential (<i>U</i>_L) and the adsorption free energy of NO₃^- (Δ<i>G</i>_*NO₃), identifying Δ<i>G</i>_*NO₃ as an effective activity descriptor for the NO₃RR. Among the screened catalysts, Mo-IrN₂ and Ru-IrN₂ exhibit superior catalytic performance, achieving remarkably low limiting potentials of -0.43 V and -0.19 V, respectively. Their high activity originates from the strong hybridization between Mo/Ru atoms and NO₃^- within their electronic structures, driven by charge transfer from TM to NO₃^-. This interaction optimally positions Δ<i>G</i>_*NO₃ within an ideal range for catalytic activity. Furthermore, the Mo-IrN₂ and Ru-IrN₂ catalysts exhibit remarkable selectivity for ammonia production by effectively suppressing competing hydrogen evolution reactions and parasitic byproduct pathways, highlighting their huge potential for use as NO₃RR electrocatalysts. This study presents an innovative strategy for designing efficient NO₃RR catalysts, enhancing the development of novel electrocatalysts for ammonia synthesis.