Effect of morphology of ZnO on colorimetric hydrogen sensitivity of PdO@ZnO hybrids

The PdO decorated ZnO (PdO@ZnO) colorimetric hydrogen sensor garners attention for visually detecting hydrogen leaks without relying on external electrical systems. While sensitivity optimization primarily focuses on PdO variations, the influence of the ZnO substrate effect remains less explored. PdO@ZnO hybrids with four different morphologies (sphere, rod, plate, hexagonal disk) are synthesized using an acid-base reaction. The morphology of ZnO influences PdO adsorption due to variations in surface area and oxygen defects. The chemical state of adsorbed palladium species is also affected by the ZnO charge. Among these hybrids, the PdO@ZnO hexagonal disk demonstrates the quickest response time (T₉₀; 182.4s) and the highest color difference (ΔE; 16) under exposure to 4 vol% hydrogen gas. This superior performance is attributed to the hexagonal disk's larger surface area, appropriate zeta potential, and oxygen defect, all of which enhance PdO adsorption. These findings enhance our comprehension of how morphology impacts the colorimetric hydrogen sensitivity of PdO@ZnO hybrids.