Electrospun Pd-Loaded ZnTiO ₃ /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 ZnTiO 3 /ZnO heterojunction nanotubes were fabricated by coaxial electrospinning, using a Zn(Ac) 2 –PdCl 2 –PVP/DMF outer solution and a Ti(OC 4 H 9 ) 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 ZnTiO 3, direct-bandgap ZnO, and PdO formed efficient p–n heterojunctions, promoting charge separation and surface reactivity. The optimized sensor (ZnTiO 3 /ZnO = 0.65:1, Pd = 3 wt %) exhibited an ultrahigh response (Ra/Rg = 43,680) to 1000 ppm of H 2 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 NH 3, C 3 H 6 O, CH 4, and C 2 H 6 O. Mechanistic analysis indicates that PdO lowers the activation energy for H 2 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.