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Application of CuOx-CeO2 Catalysts as Selective Sensor Substrates for Catalytic Detection of CO In H2 Fuel

Christopher S. Polster, Rong Zhang, and Chelsey D. Baertsch. School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, West Lafayette, IN 47907-2100

Proton exchange membrane fuel cells (PEMFCs) using H2 fuel are a promising source of portable power for electronic devices and transportation. However, as CO is a common poison for PEMFC electrodes and also a common contaminant in H2, it is critical to be able to detect and quantify CO contamination at low levels in concentrated H2 fuel. On-line CO detection in portable devices requires sensors with small size, low cost, low power consumption, and high sensitivity. These requirements have been met by microelectromechanical system (MEMS) signal transducers. However, all current microsensor technologies use materials that are inherently unselective to CO, give rise to detrimental false positive responses in the presence of H2, and require arrays of sensors for gas identification. A new sensor paradigm is demonstrated utilizing an intrinsically selective catalytic reaction coupled with micro thermal transduction. In this sensing mechanism, a substrate selectively and exothermically oxidizes CO to CO2, causing a measurable temperature rise that can be related to CO concentration.

CuOx-CeO2 catalysts have been shown to oxidize CO to CO2 with up to 100% selectivity in process streams containing ~10,000 ppm CO or more in H2 excess. It is critical to maximize selectivity towards CO in order to avoid false positive responses resulting from H2 oxidation. CO oxidation selectivity (relative to H2 oxidation) must be nearly 100%; the potential sensing range of the catalyst at a particular operating temperature is determined by the concentration at which selectivity drops from this value. The lower limits at which CuOx-CeO2 maintains this high selectivity were found to be 200 and 500 ppm at operating temperatures of 333 and 353 K, respectively. Thus, CuOx-CeO2 catalysts are a promising sensing substrate for ppm level detection of CO in H2 fuel by reaction calorimetry. Sensor geometry considerations explored by COMSOL simulations are discussed as they pertain to device sensitivity and efficiency.