Two‐Dimensional La ₂ CoO ₄ Perovskite Oxide Enabled by Phonon‐Resonance‐Driven Exfoliation for High‐Performance Gas Sensing

Strong electron-phonon interactions in layered Ruddlesden-Popper (RP) phase oxides, such as La₂CoO₄, present a major challenge for accessing their 2D counterparts. Here, we present a rapid and efficient exfoliation strategy that leverages the resonance between ultrasonic phonon waves and the intrinsic vibrational frequency of La-O bonds within the rock-salt interlayer, which are responsible for the strong electron-phonon coupling. By applying a continuous phonon wave at this resonant frequency, bulk La₂CoO₄ is exfoliated into 2D nanosheets within minutes. This process is significantly faster than conventional ion-insertion-based chemical exfoliation methods, which typically require several days. The resulting 2D-La₂CoO₄ possesses abundant surface dangling bonds and pronounced surface charge redistribution, enabling highly sensitive NO₂ detection at room temperature under visible light excitation. The sensor demonstrates an ultra-low detection limit of 5 ppb and a high response magnitude of 86.67% toward 1 ppm NO₂, along with excellent selectivity, humidity resistance, and long-term stability for up to 60 days. This work not only introduces a phonon-resonance-driven exfoliation strategy for layered oxides but also showcases the potential of 2D RP phase materials with undercoordinated surface sites for high-performance room-temperature gas sensing.