Development of Chemical Sensors for Pem and Sofc Systems

Proton-exchange membrane (PEM) fuel cells are being developed for both automotive (motive and/or auxiliary) and stationary (residential) power applications. Solid oxide fuel cells (SOFCs) also are being pursued for a number of power generation applications, including stationary (residential and utility), and automotive (auxiliary) power sources. For both of these types of fuel cells, the use of hydrocarbon fuels requires various levels of pre-processing (or reforming) of the fuel, either to provide a source of relative pure (CO-free) hydrogen for PEM fuel cells, or to provide a source of synthesis gas (H2 + CO) for SOFCs. In the case of PEM fuel cells, impurities like carbon monoxide, hydrogen sulfide, and ammonia, lead to rapid degradation of platinum-based anode electrocatalysts. In the case of SOFCs, the presence of sulfur (H2S) and hydrocarbons in the reformed gas can lead to degradation of the nickel-based anodes. Therefore, the sensing and metering of these minor impurities in the reformate gas streams, prior to their entry in the fuel cell stacks is warranted. The specific challenge with respect to monitoring these particular gaseous species is the presence of both hydrogen (~40 percent) and humidity (~30 percent) in the reformed gases. Thus, new strategies are required to meet these sensor development challenges. Current work at NexTech Materials is aimed at optimization of previously demonstrated CO sensors for PEM fuel cell systems, and development of new types of sensors for ammonia and sulfur. In addition, work recently has been initiated on development of higher-temperature sensors for hydrocarbons and sulfur for SOFC systems. Sensing strategies being pursued include resistive, capacitive, and galvanic modes, with materials tailored specifically for operation within the temperature and gas atmospheres of interest. An overview of these sensor development efforts at NexTech, including recent results obtained on CO and H2S sensors, is presented in this paper.