Dual-sensitization mechanism in Pd–SnSe2/SnO2 heterostructures for humidity-resistant NO2 sensing at room temperature

Noble metal catalysts play a vital role in enhancing the sensor performance of metal oxide semiconductors, yet their sensitization mechanisms in metal selenide materials remain insufficiently explored. This study presents a highly sensitive NO2 sensor based on Pd-functionalized SnSe2/SnO2 heterostructures synthesized via combined solvothermal and atomic layer deposition methods. Systematic characterization reveals that the Pd catalyst and n–n heterojunction significantly improve sensor performance, with the optimized Pd–SnSe2/SnO2 configuration exhibiting a remarkable response of 21.9 to 5 ppm NO2 at room temperature—three times higher than the unmodified materials. The sensor demonstrates exceptional features, including rapid response/recovery kinetics (7/19 s), outstanding humidity resistance (<14.7% decrease at 90% relative humidity), and a very low detection limit of 21 ppb. Combined experimental and theoretical analyses attribute these advancements to synergistic effects arising from electronic and chemical sensitization of Pd confirmed by density functional theory calculations. This work provides fundamental insights into the working mechanisms of noble metals and presents a practical strategy for developing high-performance gas sensors operating at ambient conditions with low power consumption.