Reliable and Flow Independent Hydrogen Sensor Based on Microwave-Assisted ZnO Nanospheres: Improved Sensing Performance Under UV Light at Room Temperature

Miniaturized high-performance hydrogen (H 2 ) sensors often suffer from reliability issues in terms of baseline drift and surrounding air flow. Normally, the sensors are often realized on microheaters to facilitate the redox reaction (desorption of generated water molecules at high temperature) to avoid the baseline drift, which leads to structural instability. In this paper, we report an UV ( $\lambda $ —400 nm/ $P_{o}$ — $400~\mu \text{W}/P_{i}$ —18 mW) excited ZnO nanosphere-based H 2 sensor, which is almost independent of surrounding air flow with minimum base line drift. The ZnO nanospheres are synthesized by microwave-assisted technique and characterized at a different temperatures in the presence and absence of UV light to optimize the operating condition. It can be observed that the UV irradiated sensor is getting sufficient activation energy to enable the current modulation at different temperatures (60 °C and 100 °C), including room temperature (27 °C) in different concentrations of H 2 (1% to 4%). By exploiting the UV radiation, flow independent (250-1000 sccm) with negligible baseline drift H 2 sensor is demonstrated with fast response/recovery time at room temperature (27 °C). Theoretical reasoning for sensing characteristic is attempted to explain with the help of scanning electron microscopy, X-ray diffraction, ultraviolet-visible-near infrared, and photoluminescence spectrum. Flow dependence, repeatability, cross selectivity, and humidity tests were also conducted to study the reliable issues.