Studies On The Preparation And Photoelectrochemical Performance Of Complex Copper-based Thin Film Photoelectrodes

Environmental and energy issues have led to the need for advanced renewable energy technologies.Among the various advanced technologies for renewable energy,photoelectrochemical（PEC）water splitting converting solar energy to chemical energy has provided a promising way to resolve the problems of environmental pollution and resource shortage.Photoelectrode as the important component of PEC device plays a pivotal role in solar water splitting.The advantages such as suitable band structure,favorable light absorption,and abundant elemental composition allow the copper-based semiconductor to become one of the most potential photoelectrode materials.In this study,we adopted the spray pyrolysis to prepare copper-based thin film photoelectrodes and improved their PEC performances from the respects of morphologies and surface modification.The main results as follows:（1）The copper bismuth oxides（Cu Bi₂O₄）thin film photoelectrodes with porous morphology were prepared through spray pyrolysis.The PEC performances were also improved as we understood the synthesis mechanism.In order to surmount the drawback of low carriers’separation efficiency of Cu Bi₂O₄electrode,we adjusted the concentration of citric acid to add more nanoholes in the Cu Bi₂O₄bulk.As the Cu Bi₂O₄growing on the FTO substrate,the citric acid could act as gel to trigger the in-situ gelation resulting in the self-combustion of citric acid and the production of uniform porous nanostructure.The porous structure with high crystallinity rendered many benefits such as decreasing the transport route of minority carriers,inhibiting the recombination of photo-excited carriers,and improving the quantum efficiency of Cu Bi₂O₄photoelectrodes.As we obtained an optimal porosity,the generated photocurrent at 0.6 V vs.RHE of Cu Bi₂O₄has reached 2.86 m A·cm^-2,and the internal quantum efficiency（IQE）could be over 10%.（2）As optimizing the PEC performances of Cu Bi₂O₄photoelectrodes,we also developed the dynamic spray pyrolysis for the preparation of large-area metal oxide thin film with controlled porosity.During the process of spray pyrolysis,we found the morphology can be controlled by kinetically coordinating the relative rates between the gelation and the auto-combustion of citric acid.Such a convenient technology provides a universal approach for preparing the oxide thin film with porous nanostructure as well as the controllable composition and morphology.Considering the wide application of spray pyrolysis,this technology has a huge advantage on the respects of large-area PEC photoelectrode fabrication and heterocatalysis.（3）In this study,we prepared the zinc doped copper gallium indium sulfide（CGIZS）thin film photoelectrodes by the spray pyrolysis and optimized PEC property by surface modification.The precursor thin films of CGIZS deposited through spray pyrolysis get further sulfuration in the tube furnace with dual temperature zones to obtain the CGIZS thin film.The PEC performances of CGIZS photoelectrodes get improved by modifying the Cd S and Pt.First,the n-type Cd S buffer layer was deposited on the CGIZS surface through the chemical bath deposition to construct a heterojunction structure with the purpose of improving the photovoltage and carriers’separation efficiency.Following,the Pt nanoparticles were adopted as the co-catalyst to increase the catalytic sites on the electrode surface.The generated photocurrent at 0 V vs.RHE of Pt/Cd S/CIGZS has reached 2.86 m A·cm^-2which is 10 folders greater than that of pristine CGIZS photoelectrode.Also,the Pt/Cd S/CGIZS has a more positive onset potential with a value of 1.1 V vs.RHE which is more favorable for overall solar water splitting.