| Micro/nano-structured semiconductor thin film materials are widely used in photoelectrochemistry,photocatalysis,gas sensor,medicine and so on.Cadmium sulfide(CdS)has been used as a photosensitizer of various wide band-gap semiconductor photoanodes in photoelectrochemical(PEC)cells due to its narrow direct band-gap(2.4 eV)and it can effectively absorb visible light.In this paper,we studied the preparation and the photoelectrochemical properties of micro/nano-structured CdO/CdS and ZnO/CdS semiconductor thin film photoelectric materials.1.The irregular micro-island arrays(MIA)of CdO/CdS composites on fluorine-doped tin oxide(FTO)substrates have been prepared for the first time as photoanodes without using any templates.The preparation process includes following three steps:firstly,an irregular MIA-Cd film was prepared on the FTO substrate by electrodeposition;then the MIA-Cd evolved into MIA-CdO by annealing at air;finally,an irregular MIA-CdO/CdS photoanode was obtained by modifying the MIA-CdO film with CdS nanoparticles,which was realized by successive ionic adsorption and reaction(SILAR).Their structure,composition,optical properties,and photoelectrochemical performance have been investigated.The optimized MIA-CdO/CdS composite films possess these advantages such as large surface area for light absorption and charge production,dense and wide paths for charge separation and transportation,and plentiful channels among the islands for mass transfer between the solution and the CdS surface.The photoanode displays the highest saturation anodic photocurrent density of 6.8 mA cm-2 ever reported on the CdO/CdS-based photoanodes under visible light illumination of 100 mW cm-2 in a mixed solution of 0.1 mol dm-3 Na2SO3 + 0.1 mol dm-3 Na2S,and the solar-to-electricity efficiency is 7.0%.2.The nanoporous CdO/CdS composite films are synthesized by a three-step method.First,Cd(OH)2 sol obtained by the simple chemical method with PVP as a protectant was dropped on the clean FTO and then annealing at air forming nanoporous CdO film.Finally,the CdO/CdS composite films were obtained by modifying the CdO film with CdS nanoparticles via SILAR.Their structure,composition,optical properties,and photoelectrochemical performance have been investigated.Under the optimum conditions,the photoanode displays a higher saturation photocurrent density of 5.72 mA cm-2 than most CdO/CdS-based photoanodes reported in literature under visible light illumination of 100 mW cm-2 in a mixed solution of 0.1 mol dm-3 Na2SO3 + 0.1 mol dm-3 Na2S,and the solar-to-electricity efficiency is 5.8%.Campare to the method of electrodeposition used above,this method for preparing CdO film is more convenient and simpler,but the photoelectrochemical performance of the prepared composite films is slightly poor.Thus,the MIA-CdO/CdS photoanode with island structure is benefical for improving the photoelectrochemical performance.3.The nano-structured composite ZnO/CdS films with hierarchical nanoporous and nano-cracks are synthesized by a facile two-step method.We first fabricated the hierarchical nanoporous ZnO thin film through simple and rapid gas/liquid interface assembly and layer-by-layer transfers of ZnO nanoparticles without using any templates.After annealing,the assembled ZnO film is sensitized with CdS nanoparticles by SILAR.Their structure,composition,optical properties,and photoelectrochemical performance have been investigated.Under the optimum conditions,the prepared ZnO/CdS composite films facilitate the adsorption of visible light,and the hierarchical nanoporous and nano-cracks structure is beneficial for the transfer of photoelectron,as well as the mass transfer process between the solution and the surface of the CdS.The photoanode demonstrates a higher saturation photocurrent density as high as 7.84 mA cm-2 than most ZnO/CdS-based photoanodes reported in literature under the visible light irradiation of 100 mW cm-2 in 0.5 mol dm-3 Na2S solution,and the solar-to-electricity conversion efficiency is 6.6%. |
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