Rh-Induced Oxygen Vacancies in a PdRh/SnO₂ Heterointerface for Enhanced MEMS Hydrogen Detection

High-performance hydrogen (H₂) sensors are essential for industrial safety and environmental monitoring. Herein, we report a microelectromechanical system (MEMS) H₂ sensor based on SnO₂ nanoflowers in situ decorated with PdRh nanoparticles (PdRh/SnO₂). Gas-sensing evaluations demonstrate that the sensor exhibits an ultrahigh response (R_a/R_g) of 20.2 to 100 ppm H₂, representing a nearly 4-fold enhancement compared to the conventional Pd/SnO₂ sensor. Furthermore, it displays rapid response and recovery times of merely 1.7 and 2.2 s, equivalent to ∼63 and ∼34% of those exhibited by the Pd/SnO₂ counterpart, respectively. Additionally, the device achieves a notably low detection limit below 100 ppb alongside good long-term stability. Mechanistic studies combining experiments and density functional theory (DFT) calculations reveal that this significant performance enhancement originates from a dual mechanism. While the synergistic catalytic dissociation of H₂ by the PdRh nanoalloy contributes to the improved sensing kinetics, we uncover a more critical role of Rh: it lowers the desorption energy barrier of lattice oxygen in SnO₂, thereby inducing the formation of high-density oxygen vacancies at the heterointerface. This Rh-mediated defect engineering promotes the adsorption and generation of reactive oxygen species, providing abundant active sites for H₂ reactions and substantially amplifying the sensing response. Finally, the PdRh/SnO₂-based MEMS sensor was successfully integrated into a portable wireless monitoring system, validating its tremendous potential for H₂ detection applications.