Study of a solid oxide fuel cell fed with n-dodecane reformate. Part II: Effect of the reformate composition

Abstract

The electrochemical behaviour of a Solid Oxide Fuel Cell (SOFC) fed with n-dodecane reformate is investigated. Experiments are carried out at 800 °C by using a cell consisting of a supporting Ni anode, a thin double layer yttria-stabilised zirconia/yttria-doped ceria electrolyte and a perovskite cathode. A catalytic steam reformer (SR) is used for processing the n-dodecane at 800 °C. The reformer is operated with a steam to carbon (S/C) ratio varying progressively from 3 to 1 and a gas space velocity (GHSV) equal to 16,000 h−1, in the presence of a RhCeO2ZrO2 catalyst. The composition of the reformate gas is determined by gas-chromatography before feeding the stream to the SOFC cell. An endurance test of 300 h for the coupled reformer-SOFC system shows a good stability using a range of S/C values from 3 to 1.5. Electrochemical ac-impedance spectra (EIS) and polarizations curves are carried out during the durability test to study the cell ageing. By decreasing the S/C to 1, an occlusion of the reforming reactor, as a consequence of n-dodecane cracking, occurs. Post-operation scanning electron microscopy analysis (SEM) of the SOFC cell shows that the Ni-based anode is not affected by any relevant deposition of carbon fibres including the inner pores. Whereas, the cracking process, occurring at low S/C values, is essentially involving the catalytic bed and the anode feed pipeline. However, the occurrence of high molecular weight hydrocarbons, already at S/C 1.5, causes a decrease of the cell performance. Accordingly, the best trade-off is achieved with S/C = 2.