Intrinsically Spin‐Exchange‐Field‐Modulated Two‐Dimensional Sensor with Platinum Single Atoms for High‐Performance Hydrogen Peroxide Monitoring

Single‐atom catalysts (SACs) offer broad prospects in catalysis and sensing due to their maximum atom efficiency and tunable coordination. However, the performance of Pt‐based SACs in electrochemical hydrogen peroxide (H 2 O 2 ) sensing remains kinetically limited. To overcome this, we propose a magnetic engineering strategy that introduces Fe/Co atoms adjacent to Pt sites. Through in situ pyrolysis, magnetized Pt SACs (mag‐Pt SACs) were stably anchored on a 2D electrode. This approach uses the intrinsic magnetic moments of Fe/Co to induce local spin polarization, thereby modulating the electronic structure of Pt without an external field. Compared to PtN 4 and Fe‐Co diatomic catalysts, the mag‐Pt SACs‐modified electrode exhibited significantly enhanced sensitivity—by 1.80‐ and 2.14‐fold, respectively. Mechanistic studies reveal that the induced spin polarization generates a net magnetic moment and unpaired electrons at Pt, which optimizes the d ‐band center and weakens the over‐strong adsorption of reaction intermediates, thus lowering the H 2 O 2 reduction barrier and boosting sensing kinetics. Based on this spin‐polarization enhancement, the mag‐Pt SACs biosensor achieved highly sensitive and selective real‐time monitoring of H 2 O 2 fluctuations from MSB/VK3‐stimulated cancer cells. This work introduces spin behavior into electrocatalytic kinetics, providing a new paradigm for designing high‐performance SAC‐based electrochemical sensors.