The First Principles Study Of Gas Molecule Adsorbed On ABO₃Type Oxide Surface

Solid oxide fuel cell (SOFC) as power generator has attracted considerable attention due to their high energy conversion efficiency, excellent fuel flexibility and low level of pollutant emission. At present, increasing the SOFC cathode catalytic activity at lower temperature and looking for new anode materials with resistance to carbon deposition and sulfur poisoning are needed to solve the problem for the practical technology. Rare earth-transition metal composite perovskites oxide is the preferred material to solve the problems. Rare earth element replacement, alkaline element doping and noble metal catalysis loading are main experimental means for optimization and improvement of cathode and anode material performance. A large number of experimental results have been reported. However, detailed microscopic mechanism analysis is still lack about the cause of the performance difference of different material, the role of noble metal catalysis for oxygen reduction reaction in cathode, and LaCrO3oxide is more resistant to sulfur poisoning phenomenon than Ni-based anode. In fact, the reaction mechanism of electrode, catalytic activity of different surface positions and their reliance on surface structure and defect, which are difficult to be directly obtained by experimental measurement. The first-principles calculation can make up for the loss. The first-principle calculation has proved to be a powerful tool to elucidate reaction mechanism as the technique can provide electronic structure, geometrical parameters, related energy and adsorbed intermediate species. The adsorption mechanisms of gas molecules on ABO3-type oxide surface are studied in paper. The experimental conclusion which noble metal loading promoted the O2molecule dissociation adsorption is verified. We have clarified the reason which LaCrO3based anode material is more sulfur-tolerant than traditional Ni-based anode.Bulk LaMnO3electronic structure has been investigated using first-principles calculation based on the density functional theory. We calculate electronic properties of interaction between Ag atom and LaMnO3(001) surface with6layer slab model. The comparative analysis of O2molecule adsorption properties on pure LaMnO3(001) surface and Ag loaded surface is implemented. We reveal the interaction mechanism of the O2-LaMnO3adsorption system.The adsorption properties of noble metal atoms (Ag、Pt、Pd) on La1xSrxMnO3(001) and the mechanisms of O2molecule adsorption and dissocation on La1xSrxMnO3(001) surface have been investigated. We further analysis noble metal catalytic role for O2molecule adsorption and the interaction mechanisms between O2molecule and noble metal atoms. Results indicate that the adsorption energies of O2molecule increase from0.495eV to0.591～1.118eV due to pre-adsorbed noble metal atoms. Bond length and bond population show the pre-adsorbed noble metal atoms facilitate O2molecule dissociate to O atoms. We theoretically verified the experiment conclusion that the loaded noble metals promoted the O2molecule dissociative adsorption.We have investigated surface properties of the PrMnO3(001) and oxygen adsorption on surface using density functional theory with the generalized gradient approximation (GGA+U) method. The surface rumpling of the PrO-terminated surface is much larger than that of the MnO2-terminated surface and PrO-terminated surface is rough than MnO2-terminated surface. Both the PrO-and MnO2-terminated surfaces display reduction of interlayer distance of the first layer and the second layer, expansion of the second layer and the third layer. The formation energies of oxygen vacancy on MnO2-terminated surface and PrO-terminated surface are2.764eV and3.624eV, respectively. This implies that the oxygen vacancy occurs more readily at the MnO2-terminated surface as compared with the PrO-terminated surface. The formation energy of oxygen vacancy in bulk PrMnO3is3.226eV. The oxygen vacancy formation energy of bulk PrMnO3decreases from3.226eV to0.333eV due to the doped Sr.Density functional theory calculations are employed to investigate the adsorption of H2S、SH and S on the (001) surface of LaCrO3. H2S molecule adsorption is found to be stable with H2S binding preferentially at O site on the LaO-terminated surface. The adsorption of H2S molecule leads to the electrons transferring from the substrate to the molecule and the charges rearrangement within the molecule. SH and S are found to be preferentially adsorbed at the Cr site. Both bond population and PDOS analysis show that there is hybridization between adatoms and surface Cr atoms. We predict the adsorption energies of sulfur-containing species increase following the sequence H2S<SH<S on LaCrO3(001) surface. We analyze the reason that LaCrO3is more sulfur-tolerant than traditional Ni-based anode materials from the angle of adsorption energy.