Electrochemically chlorinated graphene for ultrafast NO₂detection at room temperature

Functionalization of two-dimensional (2D) materials is a key approach to enhancing the performance of gas sensors since it effectively modulates the intrinsic chemical properties. Various atoms have been exploited to change the molecular interaction between sensing materials and target species. In particular, chlorine has been widely studied due to its extremely high surface reactivity and high electronegativity. However, traditional chlorination methods have been conducted by hazardous processes. Herein, we report a non-toxic electrochemical chlorination of graphene that enables superior nitrogen dioxide (NO₂) gas sensing properties at room temperature. Chlorinated graphene (Cl-Gr) was synthesized by an electrochemical reaction using an aqueous sodium chloride (NaCl) solution under an applied voltage. The Cl-Gr gas sensors exhibited enhanced sensitivity and improved reversibility upon exposure to NO₂at room temperature. The response and recovery times were dramatically decreased by 75.8% and 86.4%, respectively. The role of chlorine in the sensing performance was investigated by first-principles density functional theory (DFT) calculations, which were in agreement with experimental results. This work extends the potential use of functionalized 2D material-based gas sensors and deepens the understanding of their gas sensing mechanism.