The kinetics of CH4 steam reforming and partial oxidation are determined by the oxidation rate of CHx adsorbed species The modification of the Ni/YSZ and Ni/GDC with Au and/or Au-Mo results in differentiated structures of atomically dispersed Au and/or Au-Mo at the surface and the bulk of the Ni particles. At lean S/C NiAu/YSZ selectively oxidizes electrochemically the catalytically produced H2 and CO, while NiAu/GDC is selective to the direct partial electrochemical oxidation of CH4 to CO and H2. The modified electrodes show significant tolerance to C formation. Au-Mo modification enhances the intrinsic sulfur tolerance properties of Ni/GDC.
The presented work is a short review of the research attempts from our group with collaborators, during the last 15 years, which had as main objective to study and improve the electrocatalytic performance of Ni-based electrode materials for the CH4 Internal steam Reforming process (ISR.) in Solid Oxide Fuel Cells (SOFCs). In particular, NiO/YSZ and NiO/GDC anode powders were modified with Au and/or Mo nano-particles via different preparation methods. These efforts resulted in anode materials with high tolerance and improved electrocatalytic activity under both carbon forming and sulfur poisoning conditions. The most important findings are being reviewed and critical findings are being highlighted 50 as to stress the key differences in the electrocatalytic performance between Ni/YSZ and Ni/GDC. The possible effects of Au and/or Mo addition on the physicochemical and strucutral properties of the cermets are thoroughly discussed as well as active functional layers in the form of anode SOFC electrodes.