Precisely Controlled Polymerization of Two‐Dimensional Conducting Polymers in Quasi‐Liquid Layer Enables Ultrahigh Sensing Performance

Abstract Gas sensors based on conducting polymers offer great potential for high‐performance room temperature applications due to their cost‐effectiveness, high‐sensitivity, and operational advantage. However, their current performance is limited by the deficiency of control in conventional polymerization methods, leading to poor crystallinity and inconsistent material properties. Here, the quasi‐liquid layer (QLL) on the ice surface acts as a self‐regulating nano‐reactor for precise control of thermodynamics and kinetics in the polymerization, resulting in a 7.62 nm thick two‐dimensional (2D) polyaniline (PANI) film matching the QLL thickness. The ultra‐thin film optimizes the exposure of active sites, enhancing the detection of analyte gases at low concentrations. It is validated by fabricating a chemiresistive gas sensor with the 2D PANI film, demonstrating stable room‐temperature detection of ammonia down to 10 ppt in ambient air with an impressive 10% response. This achievement represents the highest sensitivity among sensors of this kind while maintaining excellent selectivity and repeatability. Moreover, the QLL‐controlled polymerization strategy offers an alternative route for precise control of the polymerization process for conducting polymers, enabling the creation of advanced materials with enhanced properties.