Exploring Fuel Flexibility of Sputtered Thin Barrier Layers SOFC Cells: The Effect of Direct Ammonia Feeding on the Performances

Abstract

We investigated the influence of the fuel change, from pure hydrogen to hydrogen-ammonia mixture at different percentage, on the electrochemical behaviour of 50 mm in diameter Solid Oxide Fuel Cells (SOFC) with sputtered thin buffer layers of Gd doped Ceria, varying the working temperatures from 800°C to 650°C. The results show that the performances of the cells are not affected by the fuel change for the high working temperatures (800°C and 750°C). As an example, a power density value of 802 mW∙cm-2 at 1 A∙cm-2 is found when directly feeding the cell with 8 Nml∙min-1cm-2 of ammonia and with an equivalent flowrate of 12 Nml∙min-1cm-2 of H2. These power density output values are comparable to those obtained in industrial State of Art (SoA) SOFC cells with screen printed buffer layers fed with higher hydrogen flowrates, thanks to the improved electrochemical performances obtained in the case of cells with sputtered thin buffer layers of Gd doped Ceria. At lower working temperatures (700°C and 650°C), slight changes in the electrochemical behaviour of the cells are observed. Nevertheless, also in this temperature range, we obtain an output current density value of 0.54 A∙cm-2 in pure ammonia flowrate of 12 Nml min-1cm-2, at 800 mV and 700°C, equal to the value observed in SoA button cells with industrial screen printed GDC barrier layer fuelled with 16 Nml∙min-1cm-2 of H2. These results pave the way towards the use of innovative SOFC structures with sputtered thin buffer layers fuelled by ammonia.