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

Abstract

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 (alpha-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 alpha-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 alpha-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 alpha-MoO3.