Visible-Light-Enhanced NO₂ Sensing Based on the Hybrid Orthorhombic/Monoclinic-PdSe₂ Nanostructures

Palladium diselenide (PdSe 2 ), as a member of two-dimensional dichalcogenides, has a puckered pentagonal structure and tends to exhibit distinct physical properties due to the various polymorphic phases. In contrast to conventionally orthorhombic PdSe 2 (O-PdSe 2 ), the fabrication of continuous metastable monoclinic PdSe 2 (M-PdSe 2 ) remains a challenge. Here, we report the polymorphic integration of orthorhombic and monoclinic PdSe 2 crystals by concisely controlled selenization engineering under Se-sufficient and Se-deficient growth conditions. Thus, the hybrid O-PdSe 2 /M-PdSe 2 (O/M-PdSe 2 ) nanostructures were fabricated for the first time. We found that the O/M-PdSe 2 nanostructures may be used as the broadband photodetector with a relatively high responsivity of 211.4 mA W –1, laying the foundation for the expansion of high-performance photoexcited gas sensors operating at room temperature. The O/M-PdSe 2 sensor exhibited extremely fast response and recovery times (132/84 s) toward 10 ppm NO 2 gas under 405 nm light illumination compared to the dark condition. In addition, according to the optical absorption spectra and ultraviolet photoemission spectroscopy analyses, the energy band alignment at the O/M-PdSe 2 interface was determined, and the detailed gas-sensing mechanism was also proposed on this basis. This work realizes the continuous fabrication of the hybrid O/M-PdSe 2 nanostructures with promisingly combined photoelectric and gas-electric properties, which may promote the development of high-performance multifunctional nanoelectronic devices to meet the global challenges of energy shortage and environmental protection.