Enhanced Hydrogen Sensing Performance at Room Temperature Employing Photoactive Hybrid Pd Nanoparticle-Decorated SiO₂@TiO₂ Core–Shell Nanospheres

In this research, a novel hydrogen (H2) gas sensing material, consisting of Pd nanoparticle-decorated mesoporous SiO2 core–TiO2 shell (Pd/SiO2@TiO2) nanospheres (NSs), is synthesized using a cost-effective layer-by-layer self-assembly strategy, resulting in mean diameters of 200 ± 14 nm for SiO2 NSs, 229 ± 6 nm for Pd/SiO2@TiO2 NSs, and 3.0 ± 0.4 nm for Pd nanoparticles that operate at room temperature (25 °C). By using the synergistic effects of Pd nanoparticles and the core–shell architecture of SiO2@TiO2 NSs, the sensor demonstrates a high response of 22.83, with rapid response and recovery times of 68 and 43 s, respectively, toward 1000 ppm of H2 at 25 °C under illumination by 625 nm light. Even under dark conditions, the sensor exhibits a high sensor response of 7.4, with fast response and recovery times of 98 and 38 s, respectively, which is due to the incorporation of nano-Schottky junctions between Pd and the TiO2 interface and n–n homo junctions between anatase and rutile phase presence in the TiO2 shell. In addition, the integration of SiO2 NSs extended the lifespan of generated electrons by reducing the rate of electron–hole recombination in the TiO2 shell. These combined effects enhance H2 sensing capabilities at 25 °C under both visible-light and dark conditions. The sensor also shows a broad detection range of 50 to 10,000 ppm of H2, repeatability, robust performance in high-humidity conditions (0–80% RH), high selectivity toward hydrogen, and long-term stability over a 3-month testing period, making the synthesized Pd/SiO2@TiO2 NSs a promising material for hydrogen sensing in real-world environments.