Theoretical investigation on H2 oxidation mechanisms over pristine and Sm-doped CeO2 (111) surfaces

Samarium-doped transition metal oxides are recognized as promising anode materials for solid oxide fuel cell (SOFC). The adsorption and oxidation of hydrogen on both pristine and Sm-doped CeO2 (1 1 1) are studied using Hubbard-U density functional theory (DFT + U). Our calculations suggest that a H atom could bind to the doped Sm atom through a secondary bonding, weaker than covalent bonding but stronger than Van der Waals force. This special H-Sm interaction facilitates H-2 dissociation (and H2O formation) step by dramatically reducing the energy barrier from 1.092 (3.540) eV to 0.532 (0.158) eV when compared with pristine CeO2 (1 1 1), indicating that Sm doping could significantly improve the catalytic activity of CeO2 for H-2 oxidation. Microkinetic modeling further confirms the crucial role played by doped Sm, and the Sm-mediated pathway is dominant at medium and low temperature (300-800 K), contributing to good low-temperature performance of CeO2-based anode in SOFC.