Preparation And Photoelectric Chemical Properties Of Pyramid-like Silicon Matrix Composites

Because of the prompt progress of economy and the change of living environment,seeking green,environmental protection,renewable alternative energy is a necessary condition for the development of human society.Hydrogen is by far the most desirable alternative energy source.Fujishima and Honda have attracted the attention of many scientists since they were the first to use renewable solar energy for photochemical decomposition of aquatic hydrogen.Among the materials that use semiconductor photoelectric chemical decomposition of water,silicon is of concern due to its merit for instance low price,abundant storage and wide spectrum absorption range.However,silicon as an electrode for photoelectric chemical decomposition of water still has some limitations,such as the high reflectivity of silicon surface resulting in low utilization of sunlight;It is easy to be passivated in aqueous solution,and the non-conductive silicon oxide film formed on the surface hinders the migration of photogenerated carriers,which will have a passive influence on the performance of the photoelectrode.In this paper,the pyramid-like silicon structure with anti-reflection properties was prepared on the silicon surface by using wet chemical lye etching method,and the Fe₃O₄@SiMPs,Fe₃O₄/Ni S/Ni₃S₄@SiMPs and Zn O@SiMPs composite was prepared by load modification on the silicon surface of the pyramid.Through a series of physical characterization and photoelectrochemical tests,the light absorption characteristics and photochemical performance of the form and construction elements of the composites were researched.The major components contained the following respects:(1)Monocrystalline silicon with pyramid-like structure was producted with wet chemical etching method,and Fe₃O₄powder was producted by one-step solvothermal method.The Fe₃O₄@SiMPs composite was prepared by dipping,drawing and temperature-programmed roasting on etched silicon substrate.XRD,XPS,DRS,SEM and EDS were applied to manifest the constitution,absorbance characteristics and form of the material.The analysis showed that the surface of the quasi-pyramid was covered with dense Fe₃O₄nano-sphere structure.Fe₃O₄@SiMPs as working electrode,the neutral electrolyte(0.5 M Na₂SO₄)under the condition of photoelectrochemical performance tests show that the composite material of the starting voltage of 0.33 V vs.RHE,maximum hydrogen light conversion efficiency of 0.082%(+1.10 V vs.RHE),the charge transfer resistance(R_ct)of 4.60 K?,in 1.23 V vs.RHE,photocurrent density of 0.10 m A/cm²,4 h in the light stability test in the current density drop is only 10%,shows that it has good stability.(2)Monocrystalline silicon with pyramid-like structure was producted with wet chemical etching.Ni Cl₂?6H₂O was used as nickel source and FeCl₃?6H₂O was used as iron source.Ni_xS_yand Fe₃O₄powders were prepared by solvothermal method,respectively.Disperse the two in glycol and mix well,Based on etched silicon,Fe₃O₄/Ni S/Ni₃S₄@SiMPs composites were prepared by drip coating process and temperature-programmed roasting.XRD,XPS,DRS,SEM and EDS were applied to manifest the constitution,absorbance characteristics and form of the material,Ni_xS_ynano-flower clusters and Fe₃O₄nano-spheres interlace each other on the surface of pyramid-like materials.Fe₃O₄/Ni S/Ni₃S₄@SiMPs as working electrode,the neutral electrolyte(0.5 M Na₂SO₄)under the condition of photoelectrochemical performance tests show that the composite material of the starting voltage of 0.29 V vs.RHE,maximum hydrogen light conversion efficiency of 0.32%(+1.21 V vs.RHE),the charge transfer resistance(R_ct)of 1.54 K?,in 1.23 V vs.RHE,photocurrent density of 0.82 m A/cm²,the photocurrent density and photohydrogen conversion efficiency were increased by 8 times and 4 times,respectively,compared with the unloaded Ni_xS_ysample,indicating that Ni_xS_ycan obviously improve the photochemical properties of Fe₃O₄@SiMPs composites,its mainly ascribed to the high conductivity of Ni_xS_yelectronic structure and its faible light assimilation in ultraviolet and visible bands.(3)Monocrystalline silicon with pyramid-like structure was producted with wet chemical etching with(CH₃COO)₂Zn as zinc source and NH₃?H₂O as reducing agent.Zn O powder was synthesized by solvothermal method.It is then dispersed in a glycol solvent and mixed well,The Zn O@SiMPs composite was producted on etched silicon chip by drip coating process.XRD,XPS,DRS,SEM and EDS were applied to manifest the constitution,absorbance characteristics and form of the material,The interlocking structure of Zn O nanorods was appeared on the line of the pyramid-like material.Zn O@SiMPs as working electrode,the neutral electrolyte(0.5 M Na₂SO₄)under the condition of photoelectrochemical performance tests show that the composite material of the starting voltage of 0.12 V vs.RHE,maximum hydrogen light conversion efficiency of 0.085%(+1.0 V vs.RHE),the charge transfer resistance(R_ct)of 1.17 K?,in 1.23 V vs.RHE,photocurrent density of 0.33 m A/cm²,the current density decreased by only 5.7%after 4 h continuous illumination,indicating that it has good stability.