Core-Shell Nanostructures of Tungsten Oxide and Hydrogen Titanate for H₂ Gas Adsorption

Nanostructured tungsten oxide is a promising material for sensing reducing gases such as hydrogen. However, this material exhibits limitations due to a poor response toward sensing at room temperature, incomplete recovery to the initial state, long response time, and a low response factor, which is not desired for explosive gases like hydrogen. In this work, we, for the first time, demonstrate that these limitations can be significantly overcome using the core-shell structure of tungsten oxide (WO3) nanorods and hydrogen titanate (H2Ti3O7) nanotubes developed and suitably defect-engineered by low-energy ion irradiation. The sensor based on the pristine core-shell heterostructure of tungsten oxide nanorods and hydrogen titanate nanotubes exhibits excellent response and selectivity to different concentrations of H2 ranging from 10 to 500 ppm. However, it requires a quite high temperature of 300 °C with response and recovery times of about 38 and 99.8 s, respectively. After irradiation, the hybrid form shows a similar level of response and selectivity, however, at a much lower temperature of about 120 °C with significantly faster response and recovery times of about 16 and 18 s, respectively. Such an ion beam-modified structure addresses critical issues of developing a gas-sensing device, such as the effects of moisture and power consumption. The experimental observations are very well in agreement with the predictions of the state-of-the-art Monte Carlo-based TRI3DYN ion-solid interaction simulation, and the gas-sensing mechanism was explained using first principles-based calculation. The study reveals that low-energy ion-induced defect engineering yields better charge transport, better binding of the gas with the surface, as well as the superior moisture-repelling ability of the surface, leading to better sensing performance than the pristine core-shell structure. This heterostructure between two nanomaterials carries complementary advantages in various aspects, such as the surface area, conductivity, and sensitivity toward a wide range and mixture of gases. Additionally, the wrapping yields good mechanical strength and flexibility, making it possible to use as a flexible sensing device made through a bottom-up fabrication technique.