Methanol gas detection of electrospun CeO2 nanofibers by regulating Ce3+/ Ce4+ mole ratio via Pd doping

Abstract The ability of cerium oxide (CeO2) to store oxygen by its own unique redox reaction between Ce3+ and Ce4+ ions will play a crucial role in gas detection. Thus, it is proposed to regulate the ratio of Ce3+ and Ce4+ ions via palladium element (Pd) doping for the purpose of enhancing methanol response. The pristine and Pd-doped CeO2 nanofibers were successfully prepared via a low-cost electrospinning method. The TEM results confirm the successful doping of Pd into CeO2 material with uniform morphologies. The XPS results reveal that the doped palladium exists as palladium oxide (PdO), and palladium doping can affect the mole ratio of Ce3+/Ce4+ and thus the gas-sensing performance of CeO2 nanofibers. The sensing results indicate that the 3% Pd-CeO2 sensor exhibits the highest response of 6.95 to 100 ppm methanol at 200 °C, nearly 4 times larger than that of the pure CeO2 sensor. Notably, the 3% Pd-CeO2 sensor can detect low concentration down to 5 ppm CH3OH with an apparent response of 1.92. The enhanced methanol sensing performance could be assigned to the synergetic effect between the Pd doping induced Ce3+/Ce4+ ratio and PdO/CeO2 p-n heterojunctions. These results suggest the proper Pd-doped CeO2 is a potential gas-sensing material for monitoring methanol gas.