Development of an impedance-based sensor for detection of catalyst coking in fuel reforming systems

A novel sensor for detecting the early stages of catalyst coking in fuel reforming systems has been developed. The sensor was manufactured by inkjet printing a colloidal suspension of ceramic powders to create thin (20 μm) catalytic and conductive elements of the sensor. The catalytic elements are composed of a Ni–YSZ cermet. The Ni–YSZ cermet was prepared with a concentration below the percolation limit (20 vol.%) of nickel, ensuring a low electrical conductivity. As coke forms on the catalyst material, the nickel nodules in the Ni–YSZ are connected by electrically conductive carbon and the conductivity of the catalyst material increases, indicating coke formation.Sensors were tested in a 1% ethylene environment to induce coking. The sensor showed a strong response to coking by producing a signal on the order of hundreds of millivolts. The mass of the coke load was determined to be below the detection limit of available thermogravimetric analyzers (TGA) (<10 μg). The coke load was further examined with a field effect scanning electron microscope (FESEM) and was found to be primarily carbon nanofibers. Carbon nanofibers 10–50 nm in diameter connected nickel nodules in the sensors catalyst material resulting in the observed change in resistance.