| Photocatalytic decomposition of water is a photoelectric effect of semiconductor materials.When the energy of the incident light is greater than or equal to the semiconductor bandgap,the light is absorbed,and the valence electron transition generates electrons and holes,thus enabling the semiconductor material to have the ability to decompose water,namely oxidation and reduction.α-Fe2O3is a semiconductor material with relatively suitable band gap and is an ideal photoanode material.Cathode materials are connected in series to form a photoelectrochemical battery system,so that oxygen negative ions in water are oxidized by the holes in the photocathode to precipitate oxygen,and electrons pass through the photocathode to generate hydrogen.α-Fe2O3has lower photocatalytic efficiency due to its lower electron mobility,lower optical absorption coefficient and higher electron hole recombination rate,resulting in low efficiency of oxygen evolution and hydrogen production in photoelectrochemical batteries.Interfacial modification refers to element doping,construction of heterostructure and surface modification.This method can adjust the band edge position of the material,reduce the recombination efficiency of electron holes,and provide more electrons to the cathode,thereby improving the efficiency of the photoelectric chemical battery.The first principle is a research method based on quantum mechanics,and the electronic structure,magnetic and optical properties of materials can be obtained through the first principle calculation.At present,the first-principles calculation based on density functional theory provides great help for understanding and developing new materials,which can be used in the field of semiconductor photocatalytic decomposition of water.This paper studies the effect of interface modification on effect ofα-Fe2O3on photocatalytic performance,the research content is:1、Determination of surface stable structure.This paper studies the bulk and surface electronic structure of theα-Fe2O3,calculated the band gap ofα-Fe2O3bulk structure is 2.1e V,which is very consistent with the band gap of 2.1e V in the experiment.It can be seen from surface formation,theα-Fe2O3（0001）crystal surface is the most stable surface.The relationship between the potential energy of oxygen atoms and the energy ofα-Fe2O3（0001）crystal surface obtained the most stable atomic configuration with Fe-O3-Fe as the surface terminal.2、Surface modification.Carbon nanomaterials Cx(Cx=C20,C24,C26)and"Li embedding"（Li@Cx）were studied to modify Fe-O3-Fe surface terminal structure,designed Cx/Fe-O3-Fe and Li@Cx/Fe-O3-Fe heterostructure.Impurity bands（IBs）were observed from the density of states and band structure.The number of IBs depends on the type of carbon nanocrystals and the interaction sites in the heterostructure.The cluster of Cxand Li@Cxintroduced on Fe-O3-Fe surface causes some magnetic disturbances.Compared with Cxcluster,The introduction of Li@Cxclusters increases the total magnetic moment.According to the absorption spectrum,Cx/Fe-O3-Fe and Li@Cx/Fe-O3-Fe structure has increased optical absorption intensity because of the impurity bands,and the enhancement of light absorption of Li@C24/Fe-O3-Fe system is the most obvious.3、Doping and constructing heterojunction.Based on the surface terminal structure of Fe-O3-Fe,we have constructed a heterostructure system（Al2O3/α-Fe2O3）and element-doped systems(Al6Fe2-xO3and Al12Fe2-xO3),the thermodynamic stability,crystal structure,electrostatic potential energy,energy band shift and oxygen evolution reaction mechanism of the two systems were studied respectively.The results show that Al2O3has no electronic contribution to the conduction band of the heterostructure system,and the heterostructure type is"type III".According to the Gibbs free energy"step diagram"of the oxygen evolution reaction of the two systems,it is understood that the element doping system is more advantageous to the oxygen evolution reaction than the heterostructure system. |
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