Catalytically Enhanced Near Room‐Temperature Hydrogen Sensing Using Pd‐ZnO Colloidal Crystals

Hydrogen (H 2 ) is a promising clean energy carrier that requires sensitive and selective detection technologies. In this study, palladium (Pd)‐decorated zinc oxide (ZnO) colloidal crystal (CC) sensors were fabricated and systematically investigated for hydrogen sensing at 33°C. Monodisperse ZnO nanospheres with tunable sizes were synthesized via a one‐step microwave‐assisted method and self‐assembled into uniform CC monolayers. Among the investigated structures, sensors based on 100 nm ZnO nanospheres exhibited the highest performance, owing to improved Pd distribution, enhanced charge transport, and efficient surface utilization. The Pd‐ZnO CC sensors demonstrated significantly enhanced response and selectivity toward hydrogen. The optimized 3 nm Pd‐100 nm ZnO sensor showed excellent repeatability (∼99% with and without UV illumination at 500 ppm H 2 ) and achieved an ultra‐low limit of detection of 82 ppb under UV illumination and 2.8 ppm in the dark, operating at 33°C and 9V. The sensor also exhibited good selectivity against industrially relevant interfering gases, stable performance, no memory effect, and reproducible responses across independently fabricated devices. DFT calculations elucidated the adsorption behavior and electronic interactions underlying the sensing mechanism. These results highlight the potential of Pd‐ZnO CC sensors for low‐power H 2 leak monitoring in hydrogen production, storage, transport, and fuel‐cell applications.