Influence of the Heating Rate on the Annealing Treatment of Iron Oxide Nanostructures Obtained by Electrochemical Anodization under Hydrodynamic Conditions

Abstract

[EN] Iron oxide nanostructures are promising materials for photoelectrochemical applications such as water splitting. In this work, electrochemical anodization of iron is used to form different iron oxide nanostructures, and the influence of different anodization parameters was studied in order to find the most suitable nanostructure for photocatalysis applications. On the one hand, hydrodynamic conditions were evaluated by stirring the electrode at different rotation speeds during the electrochemical anodization to check their influence on the formation of the nanostructures. On the other hand, different heating rates during the annealing treatment were studied for obtaining efficient iron oxide nanostructures. The synthesized nanostructures were characterized by different techniques such as photocurrent density vs. potential measurements, Field Emission Scanning Electron Microscopy, Raman spectroscopy and Incident Photon-toelectron Conversion Efficiency (IPCE). The results revealed that the best heating rate during the annealing treatment is 15 ºC·min-1 and that the hydrodynamic conditions allow the formation of nanotubular iron oxide structures achieving ~0.1 mA·cm-2 at 0.5 V (vs. Ag/AgCl) in the water splitting measurements. Moreover, all the nanostructures are mainly composed by hematite (¿-Fe2O3) with some amount of magnetite (Fe3O4) in their structure. Finally, the IPCE measurements showed that the best rotation speed during the electrochemical anodization for the formation of an efficient iron oxide nanostructure for photocatalysis applications is 1,000 rpm.