First-principles Study On Ru₁/TiO₂ And Ru₁-N₁/TiO₂ Single-atom Catalysts For Photocatalytic Water Splitting For Hydrogen Production

For its high chemical stability,strong photocatalytic activity,nontoxicity and inexpensiveness,titanium dioxide?Ti O₂?is a very important photocatalyst and widely used in energy conversion,environmental treatment and other fields,especially for hydrogen production from photocatalytic water splitting.Unfortunately,the practical applications of Ti O₂ are severely limited by its large intrinsic band gap,which can only absorb the ultraviolet part of solar energy.Therefore,we first design a Ru₁/Ti O₂single-atom catalyst.Next,based on the idea of charge complementation,we innovatively propose a Ru-N dimer-doping strategy to improve the performance of Ru₁/Ti O_2.Finally,we explore at the atomic scale the feasibility of photocatalytic water splitting of Ru₁/Ti O₂and Ru₁-N₁/Ti O₂.In detail,we systematically study their stability,electronic structure and photocatalytic water splitting activity.The following works have been done in this thesis:1.We introduce the research status of photocatalysis,including the mechanism of photocatalytic reaction,the concept of single-atom catalyst,the relevant properties and the applications of Ti O₂,and the current situation and the future development of Ti O₂modification.Then we briefly describe the theoretical basis and the computational methodology.2.Geometric structure and electronic properties of Ru₁/Ti O₂catalyst have been investigated by first-principles calculations.The defect formation energy calculation result shows that the oxygen-rich growth condition is conducive to the substitution of Ru atoms.The Gibbs free energy of Ru₁/Ti O₂ catalyst is reduced to-0.19 e V,showing better catalytic activity than Ti O₂.In addition,there are several intermediate bands composed of impurity energy levels in the forbidden band.It is found that some of the intermediate bands can reduce the excitation energy of photogenerated electrons to 1.95 e V,but the other localized unoccupied states will become the recombination centers of photogenerated carriers,which is not conducive to the improvement of photocatalytic activity.3.We propose a universal Ru-N dimer co-doping method to study the effects of charge compensation on the stability,electronic structure and photocatalytic water splitting for hydrogen production of Ru₁-N₁/Ti O₂ catalysts.The results show that the N dopant promotes the substitution of Ru for Ti on the Ti O₂?101?surface by the chemical bond between Ru and N,thus enhancing the stability of the whole system.Furthermore,it is found that Ru₁/Ti O₂and Ru₁-N₁/Ti O₂ show different photocatalytic properties.The absorption edge of Ru₁-N₁/Ti O₂is substantially redshifted to the visible light region,which improves the optical properties and photocatalytic activity of Ti O₂.In addition,from the thermodynamic point of view,single-atom Ru can participate in the catalytic reaction as active sites for the reduction of protons.The Ru₁-N₁/Ti O₂ catalyst has a highvisible light catalytic hydrogen production activity as metal Pd,and can also be used for commercial applications.We expect that our study of this co-doping method that simultaneously realizes band-structure tailoring and reaction dominating can provide a theoretical basis for improving the photocatalytic activity of other single-atoms loaded on oxides.