In-situ Electrochemical Fabrication And Photoelectrochemical Performance Optimization Of Nanosemiconductor Composite Films

Recently, thin films of nano-scale semiconductor photoelectric materials have been widely used in photoelectrochemical (PEC) solar cells, hydrogen production from water splitting, PEC sensors, optoelectronics, photocatalysis and so on. In this thesis, we fabricated thin films of Bi2O3/Bi2S3 and Cd(OH)2/CdS nanocomposite semiconductors by in-situ electrochemical methods, and studied their photoelectrochemical properties. The main contents are as follows:(1) Preparation and optimization of thin passive films of Bi2O3/Bi2S3 nanocomposite semiconductors by in-situ cyclic voltammetry (CV). Typically, thin passive films of Bi2O3/Bi2S3 nanocomposite semiconductors were prepared by in-situ CV in a mixed solution of Na2SO3 and Na2S under visible light illumination, and were optimized in-situ with an appropriate thickness for PEC performances according to the photocurrent change with time. The electrochemical behavior of Bi electrode in a mixed solution of Na2SO3 and Na2S was investigated, and the PEC properties of the Bi2O3/Bi2S3 nanocomposite semiconductors passive films that were obtained by CV under visible light illumination and in dark were also compared. Higher anodic photocurrent density was obtained from-1 V to 10 V on the Bi2O3/Bi2S3 semiconductor passive film prepared under light illumination than in dark. It was observed that under galvanostatic operation the anodic potential went back and forth between -1.1 V and 9.8 V rapidly while the visible light illumination was on and off. The new PEC phenomena were discussed. The results show that the PEC properties of the Bi2O3/Bi2S3 nanocomposite passive films can be monitored and optimized conveniently by CV under light illumination.We also fabricated Bi2O3/Bi2S3 nanocomposite semiconductors films in other ways. In comparison with those methods, the treatment of Bi electrode in situ by CV in mixed solution of Na2SO3 and Na2S under visible light illumination was more facile, and the obtained film in this way displayed better PEC performance.(2) Fabrication and optimization of thin films of Cd(OH)2/CdS nanocomposite semiconductors in situ by anodic polarization. Typically, the thin films of Cd(OH)2/CdS nanocomposite semiconductors were prepared by in-situ anodic polarization in a mixed solution of NaOH and Na2S under visible light illumination, and optimized in situ with an appropriate thickness for PEC performaces according to the photocurrent change with time. The electrochemical behavior of Cd electrode in the mixed solution of NaOH and Na2S was investigated. The influences of polarization potentials, polarization time and the visible light illumination on the photoelectrochemical performance were also investigated. The polarization time could be shortened under light illumination. The film of Cd(OH)2/CdS nanocomposite semiconductors prepared by in-situ anodic polarization displayed good PEC properties. In addition, we also prepared thin films of Cd(OH)2/CdS nanocomposite semiconductors by in-situ CV under visible light illumination, and the films displayed good PEC properties as well.