ppb-Level Selective Hydrogen Gas Detection of Pd-Functionalized In₂O₃-Loaded ZnO Nanofiber Gas Sensors

Pd nanoparticle-functionalized, xIn₂O₃ (x = 0.05, 0.1, and 0.15)-loaded ZnO nanofibers were synthesized by an electrospinning and ultraviolet (UV) irradiation method and assessed for their hydrogen gas sensing properties. Morphological and chemical analyses revealed the desired morphology and chemical composition of the synthesized nanofibers. The optimal gas sensor namely Pd-functionalized, 0.1In₂O₃-loaded ZnO nanofibers showed a very strong response to 172-50 ppb hydrogen gas at 350 °C, which is regarded as the optimal sensing temperature. Furthermore, the gas sensors showed excellent selectivity to hydrogen gas due to the much lower response to CO and NO₂ gases. The enhanced gas response was attributed to the excellent catalytic activity of Pd to hydrogen gas, and the formation of Pd/ZnO and In₂O₃/ZnO heterojunctions, ZnO-ZnO homojunction, as well as the formation of PdH_x. Overall, highly sensitive and selective hydrogen gas sensors can be produced based on a simple methodology using a synergistic effect from Pd functionalization and In₂O₃ loading in ZnO nanofibers.