Methane/steam global reforming kinetics over the Ni/YSZ of planar pre-reformers for SOFC systems

A solid oxide fuel cell (SOFC) is a promising all-solid-state energy conversion device that produces electricity by electrochemically combining a fuel with an oxidant across an oxide electrolyte. To optimize SOFC performance, it is necessary to investigate the effects of the design and operating parameters on system components such as pre-reformers and afterburners. In pursuit of this, a multi-component SOFC design based on a planar stack was developed. Two specially designed planar-type steam pre-reformers (the first consisting of five layers with air heating and the other of one with electric heating) utilizing nickel yttria-stabilized zirconia (Ni/YSZ) as catalyst were built to investigate the kinetics of steam reforming with methane. Whereas experimental results on the global reaction kinetics of a Ni-based catalyst in the 5-layer planar pre-reformers within a temperature range of between 350 °C and 610 °C have been published, this work reports the results of reforming kinetics using a 1-layer reformer as a flow reactor in a higher temperature range (500 °C–740 °C), as well as on reforming kinetics in combination with anode off-gas recycling. The results confirm the proposed kinetic expression of the Arrhenius type (second order with respect to the mole fraction of methane and first order with respect to the mole fraction of water) for different steam-to-carbon ratios and also for anode off-gas recycling. The activation energy for methane steam reforming corresponds to the desorption energy of CO or H2O from the catalyst surface depending on the inlet composition of the mixture