Enhanced Hydrogen Sensing Performance at Room Temperature Employing Photoactive Hybrid Pd Nanoparticle-Decorated SiO ₂ @TiO ₂ 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.