Ultrasensitive Flexible NO₂ Sensors with Remote-Controllable ADC-Electropolymerized Conducting Polymers on Plastic

Alternating- and direct-current (ADC) bipolar electropolymerization (EP) offers an efficient and scalable approach for the lateral synthesis of conjugated macromolecules, enabling the simultaneous polymerization and deposition of large conducting polymer films with intriguing fractal-like ramified topographies onto arbitrary insulating substrates under remote control. In this study, we presented the remote synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT):anion sensing films on a plastic substrate, aimed at their use in flexible nitrogen dioxide (NO₂) gas sensors. Notably, the PEDOT:ClO₃ films exhibited excellent gas-sensing characteristics, with a sensitivity of 54.8% to 50 ppm of NO₂, minimal cross-sensitivity to other gases, and a detection limit of 0.726 parts per billion (ppb) for NO₂. The sensing mechanism of the ADC-bipolar electropolymerized PEDOT:anion films was examined using spectroscopic analysis, microstructural characterization, and interaction energy computations. The findings revealed that the enhanced sensitivity of the PEDOT:ClO₃ film was attributable to an appropriate electrostatic interaction between the counteranion (ClO₃^-) and NO₂ molecules at the molecular scale, as well as the large surface area of the film resulting from hierarchical macrostructures. This study showed the practical application of the ADC-bipolar EP method for flexible organic gas sensors.