Highly sensitive prismatic h-MoO₃ sheets for temperature-dependent chemiresistive ammonia sensor

Molybdenum trioxide (MoO₃) is an excellent material for chemiresistive gas sensors. In this report, we investigated the ammonia sensing behavior of hexagonal (h-MoO₃) and orthorhombic (α-MoO₃) MoO₃. X-ray diffraction study verified the existence of two distinct phases of MoO₃. Scanning electron microscopic images revealed that the hydrothermally synthesized h-MoO₃ showed prismatic sheets while the α-MoO₃ prepared by reflux condensation exhibited agglomerated micropellets. The presence of oxygen vacancies in h-MoO₃ was confirmed by high-resolution transition electron microscopy and X-ray photoelectron spectroscopy. The as-fabricated h-MoO₃ chemiresistive sensor showed an eight-fold higher sensing response than α-MoO₃ for ammonia. The calculated limit of detection was 0.47 ppm, and the sensor exhibited good stability for 60 days. The density functional theory simulation suggested that the relatively higher adsorption energy and charge transfer could be the reason for its higher sensitivity when compared to α-MoO₃.