Robust gas sensors that offer real-time feedback about combustion in coal-fired power plants promise greater energy efficiency with fewer harmful emissions while also improving the bottom line for power generators. Currently, no technology meets this objective. Therefore, the objectives of this project are to develop an accurate, robust, reliable, high temperature sensor offering near real-time feedback to plant operators using a novel catalytic/non-catalytic sensor design to detect target gases available for oxidization. Such a sensor would inform power plant operators how to adjust the amount of fuel and air for an optimal performance. During the 2-year project funded by National Energy Technology Laboratory, the research team, headed by WVU, includes scientists and engineers from Los Alamos National Laboratory, KWJ Engineering, and Longview Power, LLC, have developed a robust high temperature CO sensor offers the best sensitivity, selectivity, and stability in the published literature. Three materials, La<
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Sr<
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CrO<
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(LSCr) perovskite, metallic Pd-Au and nickel oxide (NiO) have been systematically studied for their feasibility of being an in-situ high-temperature CO gas sensor for coal combustion system. LSCr and Pd-Au exhibits promising performance to CO sensing below 900 �C. However, when the temperature reaches to 1000 �C, only NiO is demonstrating excellent sensitivity, selectivity and stability. Under the conditions of 0.5%-3% O<
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2<
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and 1000�C, the fabricated YSZ-based mixed potential sensor using porous NiO shows good sensitivity to ppm-scale CO, even having as high as 36 mV response to 1000 ppm CO. The effect of gas transport of sample gas, geometry and structure of NiO electrode was studied. Results show that a better gas transport is much beneficial to an improved sensitivity. NiO with porous structure is much more sensitive to CO than that with dense structure, but the 90% response time is much higher due to the slow gas diffusion. Selectivity tests on how CO<
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, CH<
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and steam affect CO sensing were also demonstrated. It?s worth noting that the potential of NiO exhibits positive relationship with CO content. We found it might be due to the electrochemical reduction of CO during the interaction with NiO at 1000 �C rather than being oxidized. Finally, because of the great potential of our NiO electrode, we managed to incorporate this sensor into a novel sensor test station in the coal-fired boiler at Longview Power LLC., Longview operates one the U.S.?s newest and cleanest coal-fired boilers, an Amec Foster Wheeler first-of-a-kind, once-through, low-mass flux, vertical tube Advanced Supercritical Boiler producing 700 MW of electricity. Our testing results shows the effectiveness of our gas sensor to provide real-time CO and O<
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sensing, and the need to improve the sensor packaging & accessories to improve the long-term stability in real operation conditions.