羰基合成与选择氧化国家重点实验室（OSSO）知识库

The reversible hydrogen and oxygen recombination reaction in semiconductor dispersion highly impede the yield increase of photocatalytic water splitting to hydrogen and oxygen. In order to inhibit such reverse reaction, it is necessary to reduce the degree of hydrogen and oxygen adsorption and activiation over co-catalyst on semiconductor. It is known that partial occupation of Pt sites by halogen ions with high electronegativity can decrease the adsorption and activation degree of hydrogen and oxygen molecules over Pt/TiO₂, by this way, hydrogen and oxygen recombination reaction can be significantly inhibited, and the overall water splitting activity can be remarkably enhanced. Nevertheless, the detail inhibition mechanism on the reverse recombination reaction by halogen ions occupation on different Pt sites is still unclear. In the present work, by comparing the fluorine ions occupation on different Pt facets, we found that the fluorine ions occupation could decrease the numbers of adsorption sites on Pt(100) and Pt(111) surface. On Pt(100) facet, a fluorine ion occupation affect the four adjacent adsorption sites for H₂ and O₂ molecules adsorption, while, on Pt(111) surface, a fluorine ion occupation could affect the six adjacent adsorption sites for H₂ and O₂ molecules adsorption. The difference of fluorine ions occupation on the Pt(100) and Pt(111) facets led to the different adsorption strength of hydrogen and oxygen molecules, which further induced the activiation difference of hydrogen and oxygen on Pt co-catalyst. The results of density functional theory (DFT) calculation indicated that the hydrogen and oxygen adsorption energies on F/Pt(100) were higher than that on F/Pt(111) surface. The H₂/O₂-TPD, cyclic voltammetry and in-situ XPS experimental results also verified that the hydrogen and oxygen adsorption on F/Pt(100) surface was stronger than that of F/Pt(111) surface. The hydrogen and oxygen recombination experimental results showed that the hydrogen and oxygen recombination rates over F/Pt(100) surface was higher than that of F/Pt(111) surface. Upon light irradiation, the F/Pt(100)/TiO₂ photocatalyst exhibited lower activity for overall water splitting than F/Pt(111)/TiO₂ photocatalyst. Results in this paper provide a new avenue to promote seimiconductor catalyst for over-all water splitting by tuning the adsorption sites of hydrogen and oxygen on co-catalyst surface.