Low detection limit and high sensitivity NO₂ gas sensor based on PdO/NiMoO₄/NiO ternary composite materials

Developing nitrogen dioxide (NO₂) gas sensors that simultaneously deliver high sensitivity, selectivity, and long‑term stability remains a considerable challenge for practical applications. In this work, nanoflower‑like PdO/NiMoO₄/NiO composites with tunable PdO loadings were fabricated via a hydrothermal method combined with in‑situ impregnation and annealing. The constituent nanosheets measure approximately 200 nm in length and 20 nm in thickness. The optimized sensor with 0.5 wt% PdO loading achieves a response of 59.94 toward 1 ppm NO₂ at 160 °C, representing a 3.7‑fold enhancement over the unmodified NiMoO₄/NiO sensor, along with good selectivity and long‑term stability. This performance improvement is attributed to the synergistic effects of heterojunction formation and PdO catalytic activation, which facilitate charge transfer and surface reaction kinetics. These results demonstrate the potential of the ternary composite for practical NO₂ detection.