| Semiconductor photoelectrochemistry is a significant way for obtaining the sustainable and clean energy by utilizing solar power to generate H2 through the reducting reactions of H2O.The oxidation reaction of water decomposition can offer electrons to reducting reaction,however the oxidation reaction is difficult and becomes the bottleneck of converting solar energy into H2.Thus the oxidation reaction on the low-cost photoanodes becomes the research hotspot in rencent years.Among various material candidates for photoanodes,?-Fe2O3 has aroused widespread research interest as it is non-toxic,non-polluting,abundant and possesses a suitable band gap of 2.1 eV with the theoretical photocurrent density up to 12.6 mA/cm2.However,several inherent drawbacks impede the practical photocurrent density,such as the low light absorptivity,short lifetime of the excited-state carriers,low conductivity,short hole diffusion length,surface state and so on.The methods of improving ?-Fe2O3 photoelectrochemical performance include morphology control,element doping,surface treatment by coating passivation overlayers and loading cocatalysts,and heterjunction building.In this study,we prepared ?-Fe2O3 nanotubes to improve the low absorptivity and short hole diffusion length of?-Fe2O3,Meanwhile,focusing on the surface state,we prepared ?-Fe2O3 films modified with different thickness of amorphous Fe2O3.The main contents were discussed as follows.1?ZnO nanorod arrays templates were fabricated by hydrothermal method,then preparing ?-Fe2O3 nanotubes in the Fe3+ solution by direct ultraphonic,untraphnio+immersion and direct immersion,respectively.The sample prepared by direct ultraphonic could not remove ZnO completely,and the sample prepared by untraphnio+immersion are caducous,therefore these two methods could not be used to prepare ?-Fe2O3 nanotubes.The sample prepared by direct immersion were compact and close integration with FTO substrate.2.Preparing ZnO nanorods by 3 h,6 h and 12 h hydrothermal method,then immersing in the Fe(NO3)3 solution for 1.5 h,2.5 h and 3 h respectively for dissolving ZnO completely.The sizes of nanotubes length,wall thickness and bore diameter are ?-Fe2O3 nanotubes prepared by 12 h hydrothermal ZnO nanorods after 2.5 h Fe(NO3)3 solution immersion>?-Fe2O3 nanotubes prepared by 6 h hydrothermal ZnO nanorods after 2 h Fe(NO3)3 solution immersion>?-Fe2O3 nanotubes prepared by 3 h hydrothermal ZnO nanorods after 1.5 h Fe(NO3)3 solution immersion.The charge transfer resistance at the semiconductor-liquid junction of a-Fe2O3 nanotubes prepared by 6 h hydrothermal ZnO nanorods after 2 h Fe(NO3)3 solution immersion was least and the photcurrent density is highest.3?Preparing ?-Fe2O3 thin films with different thickness by magnetron sputtering.The photocurrent density of 37 nm ?-Fe2O3 was the highest.4?Preparing ?-Fe2O3 films modified with different thickness of amorphous Fe2O3 by magnetron sputtering.With increasing the thickness of amorphous Fe2O3,the surface state of?-Fe2O3 was covered gradually.When modified with 50 nm amorphous Fe2O3,the photovoltage rised by 0.7 V,indicating that amorphous Fe2O3 can passivate surface state of?-Fe2O3.Futhermore the injection efficiency was the highest and the transfer resistance at the semiconductor-liquid junction was the least,indicating that holes at the semiconductor-eletrolyte interface could participate in the oxidation reaction better.However,the charge resistance was the highest,indicating that amorphous Fe2O3 has low conductivity and the amount of charges reaching semiconductor-eletrolyte interface reduced.Hence the photocurrent density of a-Fe2O3 films modified with 50 nm amorphous Fe2O3 was less than that of ?-Fe2O3 under the high potential. |
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