Understanding the oxygen-vacancy-related catalytic cycle for H2 oxidation on ceria-based SOFC anode and the promotion effect of lanthanide doping from theoretical perspectives

Abstract

Lanthanide-doped ceria is known to be a promising solid-oxide-fuel-cell (SOFC) anode material. Understanding the catalytic cycle of fuel oxidation reaction on lanthanide-doped ceria is of great significance for the design of CeO2-based anode materials and catalytic processes with improved activity. Herein, we performed density functional theory (DFT) calculations on pure and Pr-, Nd-, Sm-, Gd-doped CeO2(111) to investigate the catalytic cycle of oxygen vacancy (Ov) generation and recovery in H2 oxidation process. Lanthanide doping promotes H2 dissociation, H2O formation, H2O desorption, and bulk O2− diffusion steps in the catalytic cycle. On the basis of thermodynamic and kinetic analysis, we propose that under anodic SOFC conditions, there is not a single stable Ov on pure, Pr-, Nd-, and Sm-doped surfaces because the first nearest-neighbor Ov is filled immediately upon formation, followed by the next catalytic cycle, while one Ov exists stably on Gd-doped surface, and subsequent catalytic cycle proceeds on the second nearest-neighbor vacancy site. The presence of a single Ov reduces the catalytic activity for H2 oxidation reactions on Gd-doped surface. Sm-doped ceria showed the best promotion effect for the whole Ov-related catalytic cycle, in agreement with the experimental observations.