3.4% Solar‐to‐Ammonia Efficiency from Nitrate Using Fe Single Atomic Catalyst Supported on MoS2 Nanosheets

Abstract Electrochemical synthesis of NH 3 is a carbon‐free alternative to the traditional Haber–Bosch process. Obtaining NH 3 from environmental pollutants, such as nitrates or nitrites, is a more practical route than from the nitrogen reduction reaction (NRR) due to the difficult cleavage of the inert triple bond of nitrogen gas. Here, a novel heterogeneous catalyst is reported based on iron (Fe) single‐atoms supported on 2D MoS 2 (Fe‐MoS 2 ) for the nitrate reduction reaction (NO 3 RR). Fe‐MoS 2 exhibits remarkable performance with a maximum Faradaic efficiency of 98% for NO 3 RR to NH 3 at an onset potential of − 0.48 V versus the reversible hydrogen electrode (RHE) as confirmed by the isotopic nuclear magnetic resonance (NMR) analyses. Density functional theory (DFT) calculations reveal that the enhanced selectivity for the production of NH 3 from single Fe atoms supported on MoS 2 is attributed to a reduced energy barrier of 0.38 eV associated with de‐oxidation of *NO to *N. The catalysts are coupled to an InGaP/GaAs/Ge triple‐junction solar cell to demonstrate a solar‐to‐ammonia (STA) conversion efficiency of 3.4% and a yield rate of 510 µ g h −1 cm −2 . The results open new avenues for the design of single‐atom catalysts (SAC) for the realization of solar‐driven ammonia production.