High‐Density Quintuple Single‐Atom Promoters for Enhanced Dual‐Polarity Electrochemiluminescence via Efficient Oxygen Activation

ABSTRACT Electrochemiluminescence (ECL) is a light emission process mediated by electrochemically produced radical intermediates, yet conventional luminol‐based systems are limited by sluggish oxygen activation, causing unbalanced anodic and cathodic reactions and inefficient luminescence. In this study, we report a cascade anchoring strategy for scalable synthesis of a high‐density quintuple‐metal single‐atom catalyst (HDQ‐SAC) as an ECL promoter, featuring atomically dispersed Co, Fe, Mn, Ni, and Cu stabilized by nitrogen coordination (13.79 wt% total metal loading). Comprehensive x‐ray absorption near‐edge structure, extended x‐ray absorption fine structure, and annular dark‐field scanning transmission electron microscope analyses, along with spin‐polarized density functional theory simulations, identify the delocalized network of electron transfer in HDQ‐SACs through the tailored electronegativity gradient and intermetallic synergy. This unique electronic structure of HDQ‐SACs collectively optimizes the adsorption energies of O 2 and key reaction intermediates and facilitates reactive oxygen species generation across both anodic and cathodic pathways, thereby achieving dual‐polarity ECL enhancement in the luminol‐O 2 ECL system. This multi‐atomic HDQ‐SAC promoter with cooperative oxygen activation significantly mitigates the intrinsic anodic/cathodic intensity asymmetry and establishes a mechanistic paradigm for ECL enhancement, providing a versatile framework for ultrasensitive biomarker detection.