In Situ Electron Tomography Insights into the Curvature Effect of a Concave Surface on Fe Single Atoms for Durable Oxygen Reaction

Curvature-induced interfacial electric field effects and local strain engineering offer a powerful approach for optimizing the intrinsic catalytic activity of single-atom catalysts (SACs). Investigations into the surface curvature on SACs are still ongoing, and the impact of the concave surface is often overlooked. In this work, theoretical calculations indicate that curved surfaces, particularly those with concavity, can optimize the electronic structures of single Fe sites and facilitate the reductive release of *OH. A carbon sphere featuring uniformly oriented channels and a chiral multi-shelled carbon hollow nanosphere are selected as carbon matrices due to their accessible concave and/or convex surfaces. After loading Fe species, the resulting catalysts with Fe SA in curved surfaces exhibit excellent oxygen reduction reaction activity (E