First-Principles Study of Oxygen Transfer and Hydrogen Oxidation Processes at the Ni-YSZ-Gas Triple Phase Boundaries in a Solid Oxide Fuel Cell Anode

A model of Ni-yttria stabilized zirconia (YSZ)-gas triple phase boundary (TPB) is built to simulate the oxygen transfer and hydrogen oxidation processes in solid oxide fuel cell anodes by using density functional theory. The highest barrier in the anodic processes is found in the step of oxygen transfer from the YSZ surface to the TPB site, where the oxygen is connected with nickel and yttrium/zirconium atoms. Three TPB sites and associated reaction paths, near Y or Zr atoms, and one nickel site on the Ni terrace are compared for the hydrogen oxidation reaction. Depending on the local structures of TPB sites, the reaction barrier of the (O + H)∗ → OH∗ reaction varies from 0.46 to 0.57 eV, and the reaction barrier of (OH + H)∗ → H₂O∗ varies from 0.83 to 1.05 eV. When O or OH is on the Ni site, which is only 3 Å from the Y at TPB site, the reaction barriers of the above reactions are 1.15 and 1.02 eV, respectively.