PdO-Modified Hollow In₂O₃ Nanospheres for CO Detection in Humidity Environment

Pure In2O3 and In2O3 loaded with 1, 2, and 3 mol% PdO (PdIn-1, PdIn-2, and PdIn-3) were successfully synthesized via simple hydrothermal and reduction methods. The characterization results revealed that the hollow nanosphere morphology of In2O3 was not destroyed after the introduction of PdO. The PdIn-2 exhibited bigger specific surface area (45.16 m2/g) than that of pure In2O3 (32.91 m2/g). The CO sensing results showed that PdIn-2 lowered the optimal operating temperature of the sensor (from
$280~^{\circ }$
C to
$240~^{\circ }$
C) and reduced the response recovery time (from 10/110 s to 6/109 s for 500 ppm CO) compared to pure In2O3 sensor. At the optimum operating temperature, the PdIn-2 sensor achieves a response of 4.15 for 100 ppm CO, which is 3.7 times the response of pure In2O3. Additionally, PdIn-2 maintained good CO detection capability even at higher relative humidity levels (89% RH). Besides, the PdIn-2 sensor also has better selectivity and long-term stability for CO. The improvement of gas-sensitized performance is mainly attributed to the chemical sensitization and electron sensitization effects of PdO. This study indicates that PdO-modified In2O3 hollow nanospheres are promising materials for sensitive CO gas detection with low humidity interference.