The interplay between defects, heteroatom doping, and surface curvature in carbon nanostructures governs their electronic transport and catalytic properties, yet it remains poorly understood. Here, we elucidate how structural defects, N/O functionalities, and high curvature collectively modulate morphology, conductivity, and oxygen reduction reaction (ORR) activity in carbon nano-onions (CNOs) derived from nanodiamonds (NDs). Ultradispersed NDs with tailored surface terminations are thermally transformed at 1,150 and 1,650 °C to generate partially graphitized core–shell nanostructures and fully converted, highly graphitized CNOs, respectively. X-ray photoelectron spectroscopy and electrochemical analysis reveal that pyridinic- and graphitic-N and carbonyl/phenolic O at curvature-induced defect sites define the defect chemistry, enabling fine control over charge transport and interfacial reactivity. Rotating ring-disk electrode studies show that optimally graphitized, defect-accessible CNOs (1,650 °C) deliver high specific capacitances, near-diffusion-limited ORR currents, with the number of electrons transferred per O2 molecule during ORR approximately 4.0, and a ≤10% H2O2 selectivity in alkaline media. Within a curvature-engineering framework, concentric graphenic layers introduce a Gaussian curvature that concentrates local fields and tunes *OOH binding, while continuous sp2 networks minimize resistive losses. This work establishes a structure–property–function concept for “curved” nanocarbons and defines design rules for next-generation, metal-free CNO electrocatalysts.
Zajac et al. (2026) studied this question.