Interfacial proton conduction in MXene/NTO for ultrafast room-temperature NO₂ sensing

Two-dimensional transition metal carbides and nitrides (Ti₃C₂T_x MXene) have garnered significant attention for gas sensing applications due to their high surface area and exceptional electrical conductivity. However, simultaneously achieving high sensitivity, stability, and rapid response in MXene-based gas sensors remains a critical challenge. In this study, we report the in-situ growth of sodium titanate (NTO) nanoribbons on MXene, forming a unique MXene/NTO heterostructure that enables highly sensitive and selective detection of nitrogen dioxide (NO₂) at parts-per-billion (ppb) levels under ambient conditions. The MXene/NTO sensor delivers an outstanding response (S = 808.6 % at 50 ppm NO₂) with an ultrafast response time of ∼1 s. Even at 5 ppb, it demonstrates a fully reversible resistance signal with negligible power consumption. Mechanistic investigations attribute this exceptional performance to surface proton conduction in NTO and the interfacial electric field at the MXene/NTO junction, which enhance charge transfer and NO₂ adsorption. These findings establish MXene/NTO heterostructures as a versatile platform for next-generation room-temperature gas sensing technologies.