Electronic Structure Analysis And Photocatalytic Hydrogen Evolution Performance Research Of Several Catalysts With D¹⁰ Metal Cations

Hydrogen production from photocatalytic water splitting using particulate semiconductors is an effective method to convert solar energy to chemical energy.It has attracted extensive interest because of the simple operation,low cost,and non-polluting.However,it is undeniable that the low utilization efficiency of solar energy and serve bulk recombination of photo-excited carriers limit the industrialization of photocatalytic hydrogen generation.In this paper,I designed and selected a series of efficient photocatalysts for H₂ production through analyzing crystal structure and electronic structure of semiconductors.Furthermore,those photocatalysts were synthesized and reacted for water splitting experimentally.The results were analyzed and further guided our theoretical design on photocatalysts until the design rules for efficient photocatalysts is found.To begin with,I selected rutile GeO₂ and SnO₂ with d¹⁰ electronic configuration and Ti O₂ with d⁰ electronic configuration,and analyzed systematically their electronic structures and chemical bond information.From the view of chemical bond,the HOMOs(highest occupied molecular orbitals)were all constructed by O-2p non-bonding orbitals,however,the LUMOs(lowest unoccupied molecular orbitals)originated from the anti-bonding of Sn/Ge 5s-4s orbitals and O 2p orbitals for Ge/Sn with d¹⁰ configuration and the anti-bonding of Ti 3d orbitals and O 2p orbitals for Ti with d⁰ configuration,respectively.Thus,for GeO₂,the conduction band minimum(CBM)is mainly composed of Ge–4s orbitals whereas the valence band maximum(VBM)is contributed by O-2p orbitals.Differently,the CBM of Ti O₂ is contributed mainly by Ti-3d orbitals.Considering the spherical shape of the s orbital,an isotropic extension is beneficial for electron migration of GeO₂.As expected,the m_h^*and m_e^*of GeO₂ are smaller than those of Ti O₂ along a axis.In addition,both the electron and hole mobilities(7559 cm²/V/s and 7 cm²/V/s,respectively)of GeO₂ are much higher than those of Ti O₂(339 cm²/V/s and 0.3 cm²/V/s).In summary,the electronic structure of GeO₂ is apparently superior in almost every aspect compared to Ti O₂,meaning that the electron configuration does matter to the electron/hole migration characteristics and d¹⁰is more favorable for photocatalysis than d⁰ metal cations in the rutile structure.Experimentally,rutile GeO₂ exhibits H₂ evolution rate of 103.2?mol/g/h under UV-light irradiation,which is 1.5 times higher than those of Ti O₂.After loading Pt?Ni co-catalysts,there are a?3.5 times enhancement of the photocatalytic H₂ generation rate.In order to expand the light response and adsorb visible light,the commonly used sensitizer?melon‘was combined by sintering along with rutile GeO₂.The composite possesses H₂ evolution rates of 21?mol/g/h under Xenon irradiation and it decreases to4?mol/g/h after applying a cut-off filter of 400 nm.Then,I analyzed in depth the electronic structures of monoclinic Ga₂S₃ and In-doped Ga₂S₃,and revealed the origin of photo-excited carriers in whole photocatalytic process(the existence of 1/3 Ga³⁺cationic vacancies result in the?unsaturated?two-coordinated S^2-,thus,the sectional 3p orbitals contributes to the VBM due to the non-bonding nature).By introduction of the In-S antibonding on the one hand and modifying the local dipole moment on the other hand,the light absorption ability and charge separation efficiency can be both enhanced by In³⁺-to-Ga³⁺substitution,and the photocatalytic H₂ evolution rate can be significantly promoted.The correlation between crystal structure,electronic structure and photocatalytic performance were revealed.Finally,the relationship between anionic doping in semiconductor and the variation of band gap was revealed,which could be verified by the case of the decreased bandgap of O-doped ZnS.For covalent-dominated or ionic-dominated sulfides,I explained the phenomenon about reduced bandgap after doping anions with higher electronegativity.The former is ascribed to the weak interaction between metal ions and O^2-,and the latter is caused by the longer ionic bond,which is induced by the local structural distortion surrounded by O^2-.More than that,I establish a general doped principle on semiconductors:the band gap could be reduced by replacing non-metal ions in host using some elements with big electronegativity.My findings provide new insights into the research about photocatalysis,thermoelectric field and photoelectric device,etc.