Electrospun Pd-Loaded ZnTiO₃/ZnO Nanotubes with Engineered Heterostructures for ppb-Level Hydrogen Sensing

Hydrogen's flammability and 4% explosion limit make its parts per billion-level detection essential for safety monitoring. However, conventional metal oxide semiconductor (MOS) sensors show low sensitivity and selectivity due to limited active sites. Here, Pd-loaded ZnTiO₃/ZnO heterojunction nanotubes were fabricated by coaxial electrospinning, using a Zn(Ac)₂-PdCl₂-PVP/DMF outer solution and a Ti(OC₄H₉)₄-PAN/DMF inner solution, followed by staged pyrolysis to generate hollow structures. The differential decomposition of polymers produced a hollow nanotube architecture that increases the surface area, provides abundant active sites, and facilitates gas diffusion. Meanwhile, the coupling of oxygen-vacancy-rich ZnTiO₃, direct-bandgap ZnO, and PdO formed efficient p-n heterojunctions, promoting charge separation and surface reactivity. The optimized sensor (ZnTiO₃/ZnO = 0.65:1, Pd = 3 wt %) exhibited an ultrahigh response (Ra/Rg = 43,680) to 1000 ppm of H₂ at 260 °C, a 50 ppb detection limit, and 20/162 s response/recovery times. Excellent selectivity is achieved, with hydrogen signals orders of magnitude higher than those for NH₃, C₃H₆O, CH₄, and C₂H₆O. Mechanistic analysis indicates that PdO lowers the activation energy for H₂ dissociation, while heterojunction band bending enhances oxygen adsorption and charge transport. This work provides a scalable strategy for high-performance hydrogen sensors with ultralow detection limits and strong anti-interference capability.