Recent advances in high performance Fe-based catalysts for electrocatalytic nitrogen reduction to ammonia: A review

Ammonia (NH₃) is a versatile chemical, critical to agriculture and various industries. Today, ammonia is further regarded as one of the most promising carbon-free energy carriers in the net-zero hydrogen economy. Traditionally, the energy-intensive Haber–Bosch process has been mainly used for producing ammonia by the thermocatalytic conversion of high-purity nitrogen and hydrogen, while also contributing to major greenhouse gas emissions due to dependence on fossil fuels. The electrochemical nitrogen reduction reaction (e-NRR) is a highly promising and attractive alternative roadmap to achieving clean and sustainable ammonia production under conditions that are sufficiently mild to be fully powered by renewable energy sources. However, the industrial adoption of e-NRR is currently hindered by its low ammonia yields and poor selectivity resulting from the limited reactivity of nitrogen molecules and the competitive hydrogen evolution reaction (HER) in aqueous electrolyte, respectively. To overcome these barriers, the development of efficient electrocatalysts for e-NRR is essential to the actual realization of this emerging ammonia production technology. Among various types of promising materials, earth-abundant Fe element presents a competitive edge for developing high-performance electrocatalytic N₂ reduction systems owing to its intrinsic activity, low cost, and ease of modification with other elements to form compounds with distinguished catalytic activity. Therefore, this review focuses on recent developments in Fe-based nanomaterials for ammonia synthesis through e-NRR. A detailed overview of the chemistry of e-NRR, its fundamentals, mechanisms, and experimental procedures is given, along with ammonia detection methods and catalyst evaluation metrics. The main part of this review explored various kinds of Fe-based catalysts encompassing the oxides, hydroxides, bimetallic catalysts, single atom catalysts (SACs), metal–organic frameworks (MOFs), and chalcogenides. The analysis and discussion revolved around key traits of the catalysts, including synthesis protocol, structural features, surface properties, and their correlation to catalytic activity based on experimental data and theoretical insights. Additionally, prevailing challenges and opportunities for further advancement of Fe-based e-NRR catalysts are provided.