Hydrogen Treated Hematite Nanostructures For Solar Water Splitting

In recent years, hematite has been one of the most promising materials for solarwater splitting due to its abundance, low cost and good stability in water and suitableband gap (2.2eV). However, the application of hematite was hindered by many factorssuch as poor electrical conductivity, short hole diffusion length (about2-4nm), andhigh over potential. Many methods have been used to modify the properties of hematiteto improve its performance for solar water splitting.In this thesis, we reported the oxygen vacancy doping, carbon coating andmorphology control to improve the performance of hematite nanostructures.In the second section of this thesis, hematite nanostructures have been synthesizedfor solar water splitting in a hydrothermal method. H2-treated hematite nanostructureswere prepared by a simple pyrolysis of NaBH4in a crucible. The photocurrent density at1.23V vs. RHE of H2-treated hematite (2.28mA/cm2) was over2.5times higher thanpristine sample. XAS and XPS data revealed that the electronic structure of H2-treatedhematite was significantly modified with the existence of surface oxygen vacancy,which was responsible for the remarkable photocurrent. Mott-Schottky data indicatedthat the H2-treatment increased carrier densities which could improve the conductivityand then the surface electrons can be rapidly transferred to improve the photocurrent.The H2-treated hematite with high efficiency can be used as a good start material toachieve better performance for practical application.In the third chapter, ammonium fluoride solution was added in the hydrothermalsynthesis process which led to the synthesis of hematite nanorods. The photocurrent ofthe product at1.23V vs. RHE (about1.68mA/cm2) is over2times higher than pristinesample. From the SEM images hematite nanorods show a larger surface area which may have better light absorption and result in the improved photocurrent.Moreover, in the third chapter we also introduced a simple way for the synthesis ofhematite nanostructures with carbon coating layer. Ultrasonic treatment in ethanolsuccessfully led to the preparation of carbon-coated hematite nanostructures, whichshowed a high photocurrent density of2.32mA/cm2at1.23V vs. RHE. SEM and TEMcharacterization clearly revealed that the hematite nanostructures were coated with a2-3nm carbon layer.