Heterointerfaces engineering in porous Cu/Cu2O/Cu7S4 heterojunctions: Towards high-performance room-temperature NO2 sensing in wireless applications

Ternary metal/metal oxide/sulfide heterojunctions, featuring high porosity and large interfacial areas, hold great promise as materials for high-performance chemiresistive NO₂ sensors. In this work, we successfully fabricated in-situ engineered MOF-derived Cu/Cu₂O/Cu₇S₄ heterojunctions with adjustable interfacial nanostructures and sensing properties by combining “top-down” etching and “bottom-up” growth strategies. The integration of a well-defined semi-coherent heterointerface and high porosity within Cu/Cu₂O/Cu₇S₄ heterojunctions significantly reduces the barrier to electron transmission at the interface by lowering the transfer impedance, thus accelerating carrier transfer and enhancing reachability for target gas detection at the active site. The optimized Cu/Cu₂O/Cu₇S₄-40 % sensor with customizable component ratios, featuring an increased R_a/R_g response value of 54.84 for 50 ppm NO₂ gas with a quick response time of just 9 s at room temperature. The sensor also demonstrates outstanding stability exceeding 7 weeks and an extremely low detection limit of 1.8 ppb. Furthermore, by integrating Bluetooth technology into our gas-sensing system, we overcame the limitations of conventional resistive transducers, achieving substantial advancements in terms of portability, low power consumption, and user-friendliness. These improvements mark a significant step forward in the development and exploration of novel room-temperature gas sensors based on Internet of Things (IoT) technology.