Emerging Single-Atom Alloys for Electroreduction of Waste Inorganic Nitrogen Sources toward Ammonia

Abstract Industrial ammonia synthesis relies heavily on the energy-intensive Haber-Bosch process with substantial CO2 emissions, which stimulates the quest for environmentally friendly alternatives. Recently, electrocatalytic reduction of waste inorganic nitrogen oxide (NOx) species, such as NO3−, NO2−, and NO, has sprouted as a promising route for ambient ammonia synthesis by utilizing advanced electrocatalysts. In particular, single-atom alloys (SAAs), as an innovative class of catalytic materials, not only inherit the merits of single-atom catalysts like high-atom utilization efficiency but also possess a multimetallic alloy effect, opening a broad prospect in electrocatalytic NOx reduction reaction (NOxRR) to ammonia. This review summarizes recent advancements in the utilization of SAAs for electrocatalytic NOxRR to ammonia. An overview of potential reaction pathways and their distinctions in NOxRR, alloying effect, associated in situ characterization techniques, and density functional theory (DFT) calculations is introduced, followed by discussing several bottom-up/top-down synthetic methods and characterization techniques for various SAAs. Subsequently, their electrocatalytic applications for NOxRR to ammonia are exemplified and discussed in detail. Lastly, potential research challenges in this field are delineated to amplify their contribution in accomplishing a neutral carbon footprint.