Pd-Doped Tin-Oxide-Based Thick-Film Sensor Array for Detection of H2, CH4, and CO

In the present work, a palladium (Pd)-doped tin oxide (SnO₂) thick-film sensor array has been developed by using solid state reaction-derived pure SnO₂ powders (starting with two initial tin precursors: SnCl₂·2H₂O and SnCl₄·5H₂O). The crystal structure of the powders and the morphology of the thick films have been characterized by using x-ray diffraction and field-emission scanning electron microscopy, respectively. Initially, the sensitivity of all the sensors of the array was studied for hydrogen (H₂), methane (CH₄), and carbon monoxide gas, followed by detailed analysis of the transient response of a 1 wt.% Pd-doped SnO₂ sensor prepared by using SnCl₄·5H₂O as a starting tin precursor, as it possessed better sensitivity for all the test gases. It is found that this sensor exhibits fast response and recovery times (1 min and 3.05 min) along with good repeatability for test gases; however, for CH₄ gas, it shows very much longer response and recovery times. The high response towards H₂ gas has been correlated well with the smallest crystallite size (18 nm) as well as the porous structure of the thick-film surface.