Defect Density Around Curvature-Induced Tip-Active Sites Dictates Volcano-Type Catalytic Performance of Metal‑Free Carbon Catalysts for Acetylene Hydrochlorination.

Metal‑free carbon catalysts have emerged as promising sustainable alternatives for acetylene hydrochlorination, yet the influence of defect density around curvature‑induced tip‑active sites on catalytic performance remains poorly understood. Here, we combine density functional theory calculations with experimental synthesis to investigate this structure-activity relationship. Theoretical calculations reveal that increasing defect density progressively strengthens acetylene adsorption but yields a volcano‑shaped trend in the reaction energy barrier. Experimentally, by employing an oxygen‑controlled carbonization strategy, we precisely tune the defect density in high‑curvature defective carbon catalysts while preserving curvature architecture, nitrogen doping level, and textural properties. The performance of HCDC catalysts exhibits a corresponding volcano‑shaped dependence on defect density, and the optimally defective HCDC‑O6 catalyst achieving 90.2% acetylene conversion. Mechanistic studies show that an optimal defect density balances adsorption strength and surface reaction kinetics, whereas excessive defects cause over binding and site poisoning. This work establishes defect density around tip‑active sites as a critical tunable parameter, providing rational design principles for high‑performance metal‑free carbon catalysts.