Iron Single-Atom Catalysts Anchored on Defect-Engineered N-Doped Graphene Reveal an Interplay between CO2 Reduction Activity and Stability

The precise engineering of vacancies in nitrogen-doped graphene (NG) presents a promising strategy for stabilizing metal single-atom catalysts (SACs) and tuning their catalytic performance. We explore the role of vacancies in NG for stabilizing iron-based SACs (Fe-SACs) by using density functional theory (DFT). First, we examine the stability of various vacancy types in graphene and NG supports, addressing the question of preferential formation of specific structural defects as potential sites for metal binding. We reveal simple rules governing the stability of vacancies and show that nitrogen doping can bring about vacancy healing. We identify preferred binding sites for Fe atoms/ions, specifically single and double vacancies, and analyze how the nitrogen-doping pattern in a vacancy affects the interaction of Fe with the SAC support. The results show that the positions of nitrogen(s) and the local charge environment significantly influence the stability of the Fe-SACs. Notably, some Fe@NG configurations, although not the most thermodynamically stable, exhibit enhanced catalytic performance, particularly for a CO₂ reduction reaction (CO₂RR). These findings offer valuable insights into vacancy engineering as a strategy for designing high-performance Fe-SACs and emphasize the interplay among vacancy types, nitrogen concentration, and catalyst stability in driving the catalytic behavior.