Sponge-like porous Pd–SnO2 with atomic-level doping for ultrafast and stable CO detection: Synergistic effects of lattice distortion and oxygen vacancies

The rapid and accurate detection of carbon monoxide (CO) is essential for environmental safety and human health. In this work, a series of sponge-like porous SnO 2 nanocomposites with varying Pd doping contents (0–5.0 at%) were synthesized via a one-step hydrothermal method. Their CO sensing properties were systematically investigated. The results reveal that Pd is incorporated into the SnO 2 lattice in the form of highly dispersed Pd 2+ species. These species facilitate the formation of a three-dimensional porous network interconnected by SnO 2 nanocrystals of approximately 5 nm in size. Gas sensing tests demonstrate that the sensor with a Pd doping content of 1.0 at% exhibits the highest response value ( R a / R g = 64 $R_a/R_g=64$ ) to 100 ppm CO at an optimal operating temperature of 150 °C, with a fast response time of 7 s and high selectivity to CO. Moreover, this sensor achieves a low detection limit of 1.455 ppm and maintains a detectable response over a 30-day testing period. X-ray photoelectron spectroscopy (XPS) analysis and density functional theory (DFT) calculations reveal that Pd doping not only introduces abundant oxygen vacancies but also activates CO molecules through strong chemisorption (adsorption energy of −1.13 eV), thereby accelerating the surface oxidation reaction kinetics. This structural design, combined with the Pd-induced catalytic enhancement (e.g., oxygen vacancy creation and strong chemisorption), provides a new strategy for developing high-performance low-temperature CO sensors.