3 research outputs found
Fuel Processing for Solid Oxide Fuel Cells
Fuel flexibility is a major advantage of SOFC technology. In addition to H2, operations with synthesis gas, biogas, alcohols, and light hydrocarbons are feasible provided that appropriate conditions are respected. The chapter reviews the operational modes and the anodic materials that have been proposed in the literature to run SOFCs with non-H2 fuels, as well as the methods that can be applied to clean the fuel feedstock from impurities (tars and species based on sulfur, nitrogen, and halogen). SOFC stacks can be run under four main configurations, depending on the position of the reformer (external or integrated) and on the possibility of directly processing the incoming fuel in the anodic electrode (Sect. 4.3). The feasibility of direct reforming or oxidation operations needs to be evaluated based on thermodynamic (Sect. 4.4) and kinetic considerations (Sect. 4.5), in order to avoid impairing the anode due to carbon formation or poisoning with impurities. Although they are still the most widespread choice, the behavior of standard Ni-YSZ cermet anodes (Sect. 4.6) poses problems in terms of sulfur and C tolerance, especially when the steam supply is lowered to achieve direct oxidation modes. Several strategies can be adopted to overcome these issues, by modification of the anodic materials (Sect. 4.7): Ni can be partially substituted or alloyed with transition or noble metals; Ni can be entirely replaced by different metals or oxides; protective barriers or oxide ion transferring or storing materials (MIEC, OSM) can be added to the standard Ni-YSZ cermet. In the case of external reforming solutions, the catalyst also experiences coking and poisoning issues, and its lifetime can be improved by strategies similar to those applied in SOFC anodes (Sect. 4.8). Several methods are available to remove impurities from feedstock: Those based on the use of alkaline sorbents and on catalytic decomposition are reviewed (Sect. 4.9)