Synthesis of iron oxide nanorods for solar water oxidation

Abstract

Hematite has been extensively studied as a promising material as it is inexpensive, nontoxic, and abundant; it also has a good visible light absorption. However, there are a few limitations of hematite, such as short minority carrier diffusion length, poor carrier transport properties and slow water oxidation kinetics which results in low water splitting efficiencies in comparison to the theoretical efficiency of 15 %. The performance of hematite could be improved through modifications to the material such as elemental doping, nanostructuring and surface treatment by surface passivation or co-catalyst loading. In this project, pristine hematite films were fabricated using hydrothermal synthesis for 1 hour, followed by annealing at 550 oC for 2 hours and 750 oC in air for 20 minutes subsequently. The films were characterized by Ultraviolet-Visible spectroscopy, X-ray Diffraction and Field Emission Scanning Electron Microscopy to investigate the physical, crystallographic and opto-electronic properties. Through photoelectrochemical measurements, the best pristine sample demonstrated a photocurrent of 0.60 mA cm-2 at 1.23 V vs. RHE. Pristine hematite films were subjected to a regrowth strategy with different hydrothermal synthesis durations followed by annealing under the similar condition as that for pristine. Hematite films with regrowth duration of 30 minutes had the best photocurrent performance of 0.90 mA cm-2 at 1.23 V vs. RHE. Incident Photo-to-Current Conversion Efficiency, Open Circuit Potential and Electrochemical Impedance Spectroscopy. Measurements were conducted to reveal the mechanism of regrowth. The hematite films with regrowth duration of 30 minutes were deposited with a thin layer of Co-Pi on the surface. The Co-Pi deposited regrowth hematite films achieved 1.15 mA cm-2 at 1.23 V vs. RHE.