Directional Curvature as a Design Lever for High-Efficiency CO ₂ Electroreduction on NiN ₄ -Doped Carbon Nanotubes

The development of efficient CO2 reduction reaction (CO2RR) catalysts remains a persistent challenge in renewable energy research. Although metal–nitrogen-carbon single-atom catalysts (M–N–C SACs) exhibit promising performance, their catalytic mechanisms are incompletely understood. In this work, constant-potential grand canonical density functional theory simulations reveal the directional curvature as a critical design lever for activating NiN4-doped carbon nanotubes (NiN4–CNTs). We demonstrate that bending direction─particularly zigzag-aligned (m, 0) and chiral-aligned (2m, m) curvature─synergistically controls both the magnitude of out-of-plane Ni displacement and electronic restructuring, enhancing dz2─p orbital hybridization with intermediates and triggering a spin-state transition. This directional tuning facilitates spontaneous *CO2δ− formation at low potentials, reducing the CO2RR overpotential by up to 62% versus planar configurations and outperforming other curvature alignments. Robust stability under electrochemical operating conditions is confirmed by constructing Pourbaix diagrams and performing constrained ab initio molecular dynamics simulations. This work establishes curvature-optimized NiN4–CNTs as high-performance CO2RR catalysts and provides fundamental insights into orbital-level regulation for SAC design.