Development of High Performance Anodes for Metal-Supported Fuel Cells

Metal-supported solid oxide fuel cells (MSCs) offer various potentials like cost reduction, improved mechanical robustness and abuse tolerance, which make them particularly attractive for use in auxiliary power units (APUs). The implementation of the metallic substrate requires specific adaption of SOFC processing technologies since sintering of functional layers at high temperatures under oxidizing atmosphere – as typically for anode-supported fuel cells – is restricted by the metallic substrate. Therefore, one of the current challenges of MSC technology is the development of an anode functional layer, which can be sintered under reducing atmospheres and improves the ability of the anode to withstand sulfur contaminations of the fuel gas. In the present work, a new anode concept is presented, which is based on a Ni/CGO cermet replacing the established Ni/YSZ cermet. In literature, the application of Gd-doped ceria (CGO) instead of YSZ is discussed to be advantageous regarding the sulfur tolerance of the anode. Due to its mixed ionic-electronic conductivity under reducing atmospheres the surface of CGO becomes electrochemically active. Thus, CGO still enables the electrochemical charge transfer required for the hydrogen oxidation if triple phase boundaries are blocked by sulfur compounds. The present study sheds light on the sintering behavior of CGO under reducing atmosphere with and without addition of Ni particles. The sintering study is supported by some preliminary results of characterizing the electrochemical performance of the Ni/CGO anodes by impedance spectroscopy. In addition, thin CGO layer is currently used as diffusion barrier layer between the anode and the metallic substrate. A systematic study of the stability of this barrier layer under anode sintering conditions is given.