The Effect of Mn Co-doping on the Electrochemical Properties of Gd0.2Ce0.8O1.9- d/Pt Model-composite Electrodes

Abstract

For solid oxide fuel cells (SOFCs) to reach widespread commercial distribution several obstacles still have to be overcome. Material-wise one of the main problems remains the optimization of the anode for use in harsh environments or operation conditions. The still prevalent anodes based on Ni/YSZ cermets offer excellent catalytic properties for hydrogen oxidation and reformation of hydrocarbon fuels. Nevertheless, when feeding a fuel containing hydrogen sulphide impurities to an SOFC, a dramatic drop in the anode performance is the consequence. Therefore, work is in progress to identify the causes of this sulphur triggered polarization resistance increase, which is partially explained by sulphur adsorption. The hope is that a more complete understanding in this degradation will help to formulate mitigation strategies as a way to prolong the life of an SOFC. In this contribution alternative SOFC anode materials are being surveyed and compared to the classic Ni/YSZ cermet. By exchanging the ionically conductive YSZ phase with e.g. gadolinium doped ceria (GDC) and/or the electronically conducting nickel with e.g. donor doped strontium titanate, formulations may be found, which increase the sulphur tolerance of an SOFC anode. Moreover, a fully oxidic anode may offer a significantly higher redox cycling stability than the conventional Ni/YSZ cermet. By using impedance spectroscopy on geometrically well-defined model-composite electrodes of alternative SOFC anode materials, we are able to separate elementary processes such as ionic and electronic conductivity as well as the chemical capacitance and the surface reaction resistance. By introducing H2S in the feed gas system the effects of sulphur poisoning on these parameters can be studied. This way a fair comparison of alternative SOFC anode materials to Ni/YSZ is possible.