High-Performance MEMS-Based Sensor for Trace H ₂ S Detection Enabled by Pd–In ₂ O ₃ Nanorods

Hydrogen sulfide (H 2 S), a highly toxic and corrosive gas, requires highly sensitive, selective, rapid, and stable trace-level detection in various industrial settings. To address the limitations of conventional metal oxide-based H 2 S sensors─such as insufficient detection limits, poor selectivity, and inadequate long-term stability─this study developed an H 2 S sensor by integrating Pd-loaded In 2 O 3 nanomaterials with microelectro-mechanical systems (MEMS) technology. A Pd–In 2 O 3 composite with a one-dimensional nanorod structure was successfully synthesized via a hydrothermal method followed by thermal treatment. Systematic characterization confirmed that Pd nanoparticles are uniformly dispersed on the In 2 O 3 surface in the metallic state. When fabricated into a MEMS-based sensor, the composite exhibited excellent overall performance at near-ambient temperature (25 ± 2 °C): a detection limit as low as 50 ppb, response and recovery times of 8 and 13 s, respectively, a selectivity ratio ≥5 (response to H 2 S compared to interfering gases such as CO, H 2, and CH 4 ), and less than 3% fluctuation in repeated tests. Theoretical calculations revealed that the adsorption energy of H 2 S on Pd–In 2 O 3 (−0.787 eV) is more negative than that on pristine In 2 O 3 (−0.679 eV), accompanied by a greater charge transfer (0.124 |e| vs 0.086 |e| for pristine In 2 O 3 ). Mechanistic analysis indicated that Pd doping not only modulates the band structure of In 2 O 3 via an electronic doping effect (forming a Schottky junction) but also acts as catalytic active sites, preferentially promoting the surface oxidation of H 2 S. The synergistic effect of enhanced adsorption affinity, accelerated charge transfer (verified by theoretical calculations), and selective catalysis significantly improves the sensor’s sensitivity, selectivity, and response speed. This work provides an effective strategy for material design and device implementation in developing high-performance, low-power, and easily integrable trace H 2 S sensors.