Molybdenum and tungsten oxide based gas sensors for high temperature detection of environmentally hazardous sulfur species

摘要

There is an increasing desire to control and monitor gas emissions from coal-fired power plants and other industrial systems. With this desire, there is a growing need for distributed gas sensors to monitor these emissions at high temperature (＞600℃), especially for pollutants such as SO_2 and H_2S. The objective of this work was to investigate molybdenum and tungsten binary and ternary oxide thick films on a chemiresistive sensor platform for monitoring of gas sulfur species. The work evaluated the SO_2 sensitivity of WO_3, MoO_3, SrMoO_4, NiMoO_4, Sr_2MgMoO_(6-δ) (SMM), Sr_2MgWO_(6-δ) (SMW), NiWO_4, and SrWO_4 compositions at 600-1000℃. The SrMoO_4 composition at both the micro- and nano-particulate scale showed the most promise in sensitivity, stability and selectivity to SO_2 up to 1000℃. Hydrothermally-synthesized nano-SrMoO_4 showed the highest sensor response with the R_(max) values of -17.2, -50.2 and -40.5 upon exposure to a 20 min pulse of 2000 ppm of SO_2 at 600℃, 800℃ and 1000℃, respectively. Similar sensitivity trends were distinguished down to 1-5 min SO_2 pulses. The nano-SrMoO_4 showed low cross-selectivity to H_2 and CO. Finally, the nano-SrMoO_4 sensor was also tested with H_2 and coal syngas containing 5-100 ppm H_2S, where high sensitivities were realized for both, but the sensing mechanism was altered in the latter (n-type to p-type semiconducting behavior). In order to better understand the sensing mechanism, extensive microstructural, electronic and chemical property characterizations were completed in this work.