<p>Electrochemiluminescence (ECL) based on the luminol-O₂ system is attractive for biosensing, yet its efficiency under neutral conditions remains extremely limited due to the poor reactivity of dissolved oxygen. Herein, we develop a phosphorus-doped cerium single-atom catalyst (Ce-N/P-C SAC) that significantly enhances luminol-O₂ ECL in neutral media. The introduction of P atoms effectively modulates the electronic structure of Ce sites, promotes the Ce³⁺/Ce⁴⁺ redox cycle, and accelerates the one-electron oxygen reduction reaction to generate abundant ·O₂⁻, leading to a 12.73-fold ECL enhancement compared with the bare electrode and a 2.13-fold increase over undoped Ce-N-C. Based on these catalytic properties, a highly sensitive ECL platform was constructed for the detection of gallic acid, achieving a wide linear range (10 nM − 10 µM) and a low detection limit of 7.42 nM. This work provides an efficient strategy for boosting neutral-pH luminol-O₂ ECL and demonstrates the practical potential of rare-earth single-atom catalysts in antioxidant determination and bioanalytical sensing.</p> Graphical abstract <p></p>