Multifunctional (NOx/CO/O2) Solid-State Sensors For Coal Combustion Control

Abstract

Solid-state sensors were developed for coal combustion control and the understanding of sensing mechanisms was advanced. Several semiconducting metal oxides (p-type and n-type) were used to fabricate sensor electrodes. The adsorption/desorption characteristics and catalytic activities of these materials were measured with Temperature Programmed Desorption (TPD) and Temperature Programmed Reaction (TPR) experiments. The sensitivity, selectivity, and response time of these sensors were measured for steps of NO, NO 2 , CO, CO 2 , O 2 , and H 2 O vapor in simple N 2 -balanced and multi-component, simulated combustion-exhaust streams.The role of electrode microstructure and fabrication parameters on sensing performance was investigated. Proof for the proposed sensing mechanism, Differential Electrode Equilibria, was demonstrated by relating the sensing behavior (sensitivities and cross-sensitivities) of the various electrode materials to their gas adsorption/desorption behaviors and catalytic activities.A multifunctional sensor array consisting of three sensing electrodes and an integrated heater and temperature sensors was fabricated with tape-casting and screen-printing and its NO x sensing performance was measured. The multifunctional sensor demonstrated it was possible to measure NO 2 independent of NO by locally heating one of the sensing electrodes.The sensor technology was licensed to Fuel FX International, Inc. Fuel FX has obtained investor funding and is developing prototype sensors as a first step in their commercialization strategy for this technology.iv

Recent Advances and Challenges in Thin-Film Fabrication Techniques for Low-Temperature Solid Oxide Fuel Cells

“…Despite the mentioned advantages of LT-and IT-SOFCs, they have not yet found widespread application. The reason for this delay is that, at such low operating temperatures, the increased polarisation losses in the electrodes and low ionic conductivity of the electrolyte make it extremely challenging to maintain high power outputs from the operating cells [47,48]. In addition, in the case of hydrocarbon-fuelled SOFCs, the high rates of carbon deposition and sulphur poisoning in the anode are two important obstacles to overcome when decreasing the operating temperature [33].…”

“…In addition, in the case of hydrocarbon-fuelled SOFCs, the high rates of carbon deposition and sulphur poisoning in the anode are two important obstacles to overcome when decreasing the operating temperature [33]. Approaches such as decreasing the thickness of conventional YSZ electrolytes and searching for alternative active materials with higher ionic conductivity at lower operating temperatures can be addressed as noteworthy attempts to encounter high ohmic resistance when operating at such temperatures [47]. In this regard, attempts have been made to develop alternative electrolyte materials for conventional YSZ, which possess higher ionic conductivities at lower operating temperatures, e.g., ceria-based oxides (gadolinia-or samaria-doped ceria), scandia-stabilised zirconia, lanthanum strontium gallium magnesium oxide, and proton-conductive materials such as BaZr 1−x Y x O 3−δ -or BaCe 1−x Y x O 3−δ -based perovskite oxides, to name a few [49][50][51].…”