Orbital Spatial Asymmetry Mediates Curvature-Dependent Modulation of Adsorption and Pathway Selectivity in TM–N–C Oxygen Reduction Catalysts

N-Doped graphene-supported transition metal single-atom catalysts (TM–N–C, where TM = Fe, Co, or Ni) are high-efficiency oxygen reduction reaction (ORR) electrocatalysts. Previous studies have observed curvature-dependent ORR performance in curved TM–N–C frameworks but reported only superficial catalytic phenomena, failing to reveal the electronic-structure essence of curvature-governed ORR pathway regulation. Realistic TM–N–C catalysts feature heterogeneous curved architectures with coexisting convex and concave metal sites, and the intrinsic linkage between curvature-induced electronic evolution and two- and four-electron ORR selectivity remains poorly understood. Herein, we systematically investigate curvature effects on the ORR activity and selectivity of dual convex/concave active sites, focusing on the underlying electronic mechanisms. We identify a distinct Janus-type curvature effect. Concave sites exhibit strong curvature-dependent adsorption and tunable ORR selectivity, whereas convex sites show negligible curvature responsiveness. Different from prior phenomenological findings, electronic-structure analysis confirms that this anisotropic behavior originates from the coupling of curvature-triggered electron depletion and asymmetric d orbital redistribution. For concave sites, increased curvature contracts bonding-related d orbitals (primarily the dyz component universally across three TM–N–C systems), reducing metal atom 3d and O 2p orbital overlap and weakening intermediate adsorption to modulate ORR pathway selectivity. In contrast, curvature-induced orbital expansion on convex sites is counterbalanced by electron depletion, resulting in weak curvature sensitivity. This work clarifies the fundamental electronic mechanism of curvature-regulated ORR pathways, overcoming the limitations of empirical research and establishing curvature engineering as a reliable electronic modulation strategy for precise control of ORR selectivity over TM–N–C single-atom catalysts.