Durability of anode supported solid oxide fuel cells on pre-reformed natural gas

Three different anode supported solid oxide fuel cells (SOFC) were tested with hydrogen, pre-reformed natural gas from which sulfur was removed, and with pre-reformed natural gas that contained sulfur. The cells were obtained from Forschungszentrum Jülich (FZJ), Energy research Centre of the Netherlands (ECN), and HTceramix SA. The reforming system includes a vaporizer for water, an autothermal reforming unit, a ZnO sulfur removal unit, and a product gas analysis system. The content of the reformate gas varied slightly depending on the sulfur content of fuel but an average content was: x[H2]=0.32, x[CH4]=0.08, x[CO]=0.07, x[CO2]=0.06, x[H2O]=0.25, x[N2]=0.22. The sulfur content in syngas was 2 vol-ppm when the ZnO reactor was not used. The geometry of the cells as delivered by all three manufactures was circular having the gas inlets for the fuel and oxidant at the middle. The flow field and current collector at the anode was a porous nickel mesh and at the cathode a porous platinum mesh. The active area of the cells was 50 cm2. At the cathode, dry air was used as the oxidant and its flow rate was constant 2075 mlN min-1 in all measurements corresponding to an oxygen utilization of 0.5 at 1.25 A cm-2. At the anode, the flow rate was set to correspond to a fuel utilization of 0.5 at 1.25 A cm-2. The results to be presented from the three different cell types are based on a test protocol including three different steps. Polarization measurements from the open circuit potential up to 1.25 A cm-2 or down to 0.6 V and back to the open circuit potential were firstly conducted at three different temperatures (i.e. 700 °C, 750 °C and 800 °C). Hydrogen was used as fuel in these measurements in order to see the quality of the cells. Secondly, the cells were loaded for 200 h at a constant current of 0.5 A cm-2 with one of the three different fuel choices at 800 °C in order to investigate the possible degradation of the cells. After the stable current loading, the polarization measurements were repeated with hydrogen in order to examine the possible degradation in more detailed. This work is part of the Integrated Project "Realising Reliable, Durable Energy Efficient and Cost Effective SOFC Systems" (Real-SOFC) supported by the European Commission. The cells studied here are the first generation cells produced in the project.