Highly Selective and Flexible HCl Sensor Enabled by Ag₂O-Functionalized Graphene Micropatterns

Graphene is considered one of the most attractive materials for next-generation gas sensor platforms owing to its high performance at room temperature, transparency, and flexibility. However, graphene exhibits inherent low selectivity and irreversible behavior in gas sensing. While various methods such as doping, grain control and metal decoration have been extensively employed to functionalize graphene, graphene sensors for strong acids have remained underexplored. Here, we present unprecedented room-temperature hydrogen chloride (HCl) detection of self-activated graphene functionalized by silver oxide (Ag₂O) nanoparticles. Ag₂O-functionalized graphene micropatterns show ultra-high selectivity to HCl with an extremely low detection limit of 5.617 parts per trillion (ppt). Density functional theory (DFT) calculations demonstrate that the strong interaction between Ag₂O and HCl, induced by charge depletion in the center parts of Ag₂O, promotes the attraction of HCl molecules. Furthermore, the unique properties of graphene, such as Joule heating and corrosion resistance to strong acids, significantly reduce power consumption, improve humidity stability, and ensure long-term stability, which have been major limitations of conventional acid sensors. This work proposes the functionalization of graphene by metal nanoparticles, extending beyond the limitations of conventional sensors, and demonstrates the potential of graphene as a next-generation sensor platform for flexible electronics.