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. © 2019, Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature.