First principles study on methane reforming over Ni/TiO2(110) surface in solid oxide fuel cells under dry and wet atmospheres

Understanding the carbon-tolerant mechanisms from a microscopic view is of special importance to develop proper anodes for solid oxide fuel cells. In this work, we employed density-functional theory calculations to study the CH4 reaction mechanism over a Ni/TiO2 nanostructure, which experimentally demonstrated good carbon tolerance. Six potential pathways for methane reforming reactions were studied over the Ni/TiO2(110) surface under both dry and wet atmospheres, and the main concerns were focused on the impact of TiO2 and Ni/TiO2 interface on CO/H2 formation. Our calculations suggest that the reaction between carbon and the interfacial lattice oxygen to form CO* is the dominant pathway for CH4 reforming under both dry and wet atmospheres, and intervention of steam directly to oxidize C* with its dissociated OH* group is less favorable in energy than that to wipe off oxygen vacancy to get ready for next C* oxidation. In all investigated paths, desorption of CO* is one of the most difficult steps. Fortunately, CO* desorption can be greatly promoted by the large heat released from the previous CO* formation process under wet atmosphere. H2O adsorption and dissociation over the TiO2 surface are found to be much easier than those over Ni, yttria stabilized zirconia (YSZ) and CeO2, which should be the key reason for the greatly depressed carbon deposition over Ni-TiO2 particles than traditional YSZ-Ni and CeO2-Ni anode. Our study presents the detailed CO* formation mechanism in CH4 reforming process over the Ni/TiO2 surface, which will benefit future research for exploring new carbon-tolerant solid oxide fuel cell anodes.