Fe‐based catalysts for nitrogen reduction toward ammonia electrosynthesis under ambient conditions

As one of the most important chemicals and carbon-free energy carriers, ammonia (NH3) has significant energy-related applications in industry and agriculture. Ninety percent of NH3 is produced by the Haber-Bosch process using high-purity N-2 and H-2 at high temperatures and pressures, which consumes about 1% of the total energy production and causes 1.4% of global CO2 emissions. The environmentally friendly electrochemical nitrogen reduction reaction (NRR) with low energy consumption is a promising alternative to the conventional Haber-Bosch process. However, the main issue is the low Faradaic efficiency and NH3 selectivity of electrochemical NRR, caused by inert nitrogen molecules and competitive hydrogen evolution reaction. As one of the cheapest and most abundant transition metals widely utilized in the Haber-Bosch process, the Fe element has presented the potential high performance for the electrochemical NRR. This article summarizes recent advances and research progress in non-noble Fe-based catalysts used for NH3 electrosynthesis. Various synthetic protocols, structure/morphology modification, performance improvement, and reaction mechanisms are comprehensively presented. Based on recent experimental and theoretical studies, we aim to illuminate the structure-property relationship and offer an excellent opportunity for engineering advanced Fe-based catalysts for nitrogen fixation. The most critical challenges and opportunities for Fe-based catalysts are also provided. This review would open up a promising avenue toward developing platinum-group-metal-free catalysts for electrochemical NRR applications in the future.