A First-Principles Study On Water-Splitting Hydrogen Production By Photocatalytic AMO₂?A=Li,Na,M=Co,Rh,Ir?

Since the 21st century,hydrogen has been considered as one of the excellent candidate energy sources that can replace fossil fuels because of its high combustion heat value,non-polluting combustion products,and wide sources.However,how to efficiently produce hydrogen is the key to the popularization of hydrogen.Visible light photocatalytic decomposition of water to produce hydrogen is a new type of hydrogen production technology.Hydrogen can be produced using inexhaustible sunlight,abundant water resources,and semiconductor catalysts.Therefore,finding a high-efficiency photocatalyst with good response in the visible light region is the key to visible light catalytic hydrogen production technology.In recent years,due to its special layered structure and high carrier mobility,AMO₂ alkali metal transition metal oxides have been successfully used as lithium-ion rechargeable batteries.However,the research on its application in the photocatalytic field is not enough.Therefore,based on the first-principles calculation based on density functional theory?DFT?,we studied the effects of different types of AMO₂ semiconductors on the photocatalytic water-splitting performance,and provide theoretical guidance and help for experimentally designing and synthesizing a new type of efficient visible light photocatalytic to produce hydrogen Catalysts.The main research content is as follows:1.The feasibility of hydrogen production by photocatalytic water splitting of NaXO2?X=Co,Rh,Ir?was calculated and analyzed by the M-06L method.The calculation results show that the energy gaps of NaXO2?X=Co,Rh,Ir?all meet the energy gap requirements for semiconductors to produce hydrogen by visible light water-splitting,and the position of their valence band and conduction band are consistent with the redox conditions reaction of water.At the same time,we find that as the atomic number gradually increases,the band gap value gradually increases.Through simulation,it is also proved that NaXO₂?X=Co,Rh,Ir?has higher light absorption in the visible light region,but as the atomic number increases,the absorption in the visible light region gradually decreases.In addition,it was found that NaXO₂?X=Co,Rh,Ir?has higher carrier mobility,and the mobility of electrons and holes is significantly different.Finally,we verified the possibility of charge space separation of photogenic carriers by calculating the electron charge density distribution on the VBM and CBM.2.The feasibility of visible light photocatalytic of LiCoO2 in Tetragonal,Trigonal,Hexagonal,and Cubic crystal systems was studied using the method of metaGGA-SCAN.The results show that all LiCoO₂ have suitable band gap values and proper valence band and conduction band positions,which meet the basic requirements of visible light water-splitting hydrogen production catalysts.Among them,tri-LiCoO₂and h-LiCoO2 have better light absorption in the visible light region than other structures,but it turns out that the structure has a smaller effect on optical absorption.Furthermore,we studied the mobility of LiCoO₂ for four structures.We can find that all LiCoO₂ has higher electron mobility than hole mobility,and the electron-hole mobility of c-Li CoO₂ is very different.The difference has a significant effect on the mobility of the carriers.