Alloy core composition effect of Pd-Au_gr-alloy@ZnO core–shell nanoparticles on hydrogen gas sensing performance

Pd-Au gradient alloy nanoparticles (Pd-Au_gr-alloy NPs) with different compositions are formed from Pd@Au core–shell nanoparticles (CS-NPs) with different Au shell thickness. Pd@Au CS-NPs with Au shell thickness of 1, 3, 5, and 7 nm are prepared by hydrothermal method. After calcination at 500 °C, each Pd@Au CS-NP becomes a Pd-Au gradient alloy NP, and their entire particle compositions are labelled as Pd-Au(1), Pd-Au(3), Pd-Au(5), and Pd-Au(7), respectively. These compositions of Pd-Au gradient alloy have high hydrogen affinity, so it can selectively absorb hydrogen to form Pd-Au_gr-alloyH_x. Interestingly, adding an outer ZnO shell covering the surface of Pd-Au_gr-alloy NPs further improves the sensitivity and selectivity for hydrogen gas sensing by accelerating the synergistic effect resulted from electronic sensitization and hydrogen absorption of the Pd-Au_gr-alloy core. Among the Pd-Au gradient alloy compositions, the Pd-Au(3)@ZnO CS-NPs sensor exhibits the best hydrogen sensing performance. The gas sensing response of Pd-Au(3)@ZnO CS-NPs sensor to 100 ppm hydrogen at the optimal working temperature of 350 °C is 169, which is significantly higher than those of Pd-Au(5)@ZnO CS-NPs (1 4 2), Pd-Au(7)@ZnO CS-NPs (70), Pd-Au(1)@ZnO CS-NPs (57) and pure ZnO NPs (12) sensors. The effect of Pd-Au_gr-alloy core compositions on hydrogen gas sensing properties is discussed in this research.