Dual-temperature H2 sensing with a wide dynamic range enabled by PdO/Pd-ZnO nanorod arrays

Hydrogen (H 2 ) safety monitoring demands sensors that operate reliably across the entire trace-to-percent-level concentration range, a persistent challenge for conventional metal-oxide systems. Herein, a temperature-gated sensing strategy is demonstrated using PdO/Pd-decorated, metal–organic framework (MOF)-derived ZnO nanorod arrays. Conformal coating of vertically aligned ZnO nanorods with a conductive Zn-catecholate (Zn-CAT) MOF, followed by thermal conversion, yields highly porous ZnO@ZnO homojunctions functionalized with PdO/Pd nanoparticles. This optimized hierarchical architecture enables a single chemiresistive device to operate in two distinct regimes. At 125 °C, it achieves trace H₂ detection (0.02–50 ppm) with a theoretical limit of 49 ppb. At 250 °C, it delivers an ultrahigh response (3632 to 1% H 2 ) while maintaining near-linear behavior up to 2.5%. Crucially, operando near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) explicitly unravels the underlying mechanism, revealing a transition from low-temperature oxygen-mediated pathways to high-temperature PdH x -assisted dissociative spillover. This continuous detection window, spanning approximately 5 orders of magnitude, bridges the gap between early-warning and catastrophic-release monitoring for full-scenario H 2 safety.