Iron Oxide Thin Films:Preparation,doping And Solar Light Driven Water Splitting Performance

As an n-type semiconductor material,hematite iron oxide（α-Fe₂O₃）is one of the most interesting materials in the field of photochemical water splitting.In addition to the appropriate band gap（².2 eV）,α-Fe₂O₃ has the advantages of low cost,good stability in aqueous solution,etc.At the same time,the theoretical photocurrent of α-Fe₂O₃ is as high as 12.6 mA/cm2,which makes α-Fe₂O₃ a very promising candidate in the field of photoelectrochemical water splitting.However,due to the several disadvantages such as poor conductivity,short hole diffusion length,the actual photoelectrochemical water splitting performance of α-Fe₂O₃ is far from the theatrical value.To improve the photoelectrochemical water splitting performance of α-Fe₂O₃,several methods have been applied including morphology control,element doping and surface treatment.In this article,we prepared nanostructured α-Fe₂O₃ thin films on fluorine doped tin oxide（FTO）substrates with different methods and investigated their photoelectrochemical water splitting performance.The main research contents include:1.Hematite（α-Fe₂O₃）nanostructured films were prepared on fluorine doped tin oxide substrates by heat treating the hydrothermally prepared precursor films.By using different additives in the hydrothermal preparations,the final hematite nanostructures could be controlled to be square prisms,nanorods and polyhedral blocks,of which the square prisms and the nanorods were vertically grown on the substrates and possessed preferred orientation along [110] direction while the polyhedral blocks were composed of small isotropic nanoparticles.When used as photoanodes,the α-Fe₂O₃ nanorod films showed much better photoelectrochemical water oxidation performance than the other two kinds of α-Fe₂O₃ films.Analyses based on XRD,SEM and electrochemical impedance spectroscopy revealed that the α-Fe₂O₃ nanorods had characteristics including small diameter,abundant through-holes,growing along [110] axis vertical to the substrate and high donor density,which are believed to contribute to the good photoelectrochemical water oxidation performance.2.W-doping porous square prisms films were prepared on FTO substrates through a facile method.The visible light-driven photoelectrochemical water oxidation performance of the W-doping α-Fe₂O₃ porous square prisms films was also investigated.It revealed that a high photocurrent density of 1.1 mA/cm2 was achieved from at 1.60 V vs.RHE.,which was higher than α-Fe₂O₃.Moreover,the photoresponse of the W-doping was found to expand from UV region to 600 nm.At the same time,the W-doping α-Fe₂O₃ films showed good stability in photoelectrochemical water oxidation.In the 4000 s of photoelectrochemical water oxidation test in 0.1 mol/L NaOH solution,the photocurrent density nearly kept constant.3.α-Fe₂O₃ nanostructured films were prepared on FTO based on the seed method.The effects of annealing temperature for the hydrothermally prepared α-Fe₂O₃ nanostructured films on the photoelectrochemical water splitting were investigated.In addition,the relationship between the thickness of the seed layer as well as the annealing temperature and the PEC performance was explored.It was found that the sample with seed layer annealed at 500 ℃ possessed the best photocatalytic activity,whose photocurrent could reach 0.64 mA/cm2 at 1.62 V vs.RHE.