Adsorption behavior of H4POn (n = 8,7,6) groups on the F,Si-doped reduced CeO1.979(100) surfaces investigated by first-principles calculations

Abstract

The adsorption properties of F,Si-doped reduced CeO1.979(100) surfaces to H4POn (n = 8,7,6) groups on KDP surfaces were studied by DFT+U method. The adsorption potential energy surfaces, stable adsorption configurations and electronic structures were calculated and analyzed. The results indicate that the surface O vacancy formation energy (EOv) was lower than the subsurface EOv on three CeO1.963(100) surfaces. The EOv of Ce0.926Si0.074O1.963(100) surface decreased, while the EOv of CeO1.926F0.037(100) surface increased. The adsorption energy of reduced CeO1.979(100) surface was higher than that of CeO2(100) surface. The stable adsorption sites of H4PO8, H4PO7, and H4PO6 groups have changed from Obri, Cebri, and Ot sites on CeO2(100) surface to Ot, Ot, and Obri sites on reduced CeO1.979(100) surface. Compared to CeO1.979(100) surface, the number of Ce-O(H4POn) bonds increased to 4 after H4POn groups were adsorbed on CeO1.958F0.021(100) surface, and the number of Ce-O(H4POn) bonds decreased by 1 after H4POn groups were adsorbed on Ce0.979Si0.021O1.979(100) surface. The reduced surfaces adsorbed with H4POn groups exhibited semi-metal properties. In H4PO7 and H4PO6 adsorption systems, the electron cloud presented irregular distribution, the spin up and down electronic states became asymmetric, so the systems appeared a certain magnetism. In symmetrical H4PO8 adsorption systems, the Ce4f and O2p states were closest to the Fermi level, and the Bader charge transfer between bonded Ce and O(H4PO8) atoms was the largest. Density of states of Ce0.979Si0.021O1.979(100) and CeO1.958F0.021(100) surfaces adsorbed with H4POn groups shifted towards high and low energy levels, respectively, indicating that F doping made the adsorption structure more stable.