Highly Sensitive Rayleigh Wave Hydrogen Sensors with WO₃ Sensing Layers at Room Temperature

Rayleigh wave hydrogen sensors based on 128° YX−LiNbO₃ substrates with WO₃ sensing layers operating at room temperature are studied. The experimental results indicate that the WO₃ layers obtained by a sol−gel method have much higher sensitivities because the sensing layers produced by the sol-gel method have small grains and high roughness and porosity. It is also confirmed that in the sol-gel method, keeping WO₃ solutions at low temperature and/or decreasing the viscosity of the solutions can decrease the grain sizes and increase the hydrogen-absorbability of the sensing layer. Under the optimized preparation conditions, the high sensitivity of the hydrogen sensors at room temperature is obtained, in which 1% hydrogen in natural air induces the frequency shift of 72 kHz at the operating frequency of 124.2 MHz.