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 = ≈0.89 V), strong methanol tolerance, and favorable long-term stability. Impressively, a solid-state flexible Zn-air battery based on this catalyst exhibits a remarkable durability over 40 h with a high peak power density of 122.1 mW cm and excellent charge-discharge performance at different bending angles. This work offers in-depth insights into the rational design of carbon supports with highly curved surfaces, offering new opportunities for the microenvironmental regulation of SACs at the atomic level.