Kinetics of Light-Driven Oxygen Evolution at Nanostructured Hematite Semiconductor Electrodes
Hematite nanostructures have been electrochemically grown by ultrasound-assisted anodization of iron substrates in an ethylene glycol based medium. This hematite nano-architecture has been tuned from a 1-D nanoporous layer (grown onto a bare iron foil substrate) to a high aspect self-organized
nanotube one (grown onto a pretreated iron foil). Well-developed hematite nanotube arrays perpendicular to the substrate with a 1 μm in length have been obtained. The nanoporous sample was characterized by pores of a mean diameter of 30 nm and an interpore distance of 150 nm, whereas
the self-organized nanotube layer consisted of nanotube arrays with a single tube inner diameter of approximately 50 nm and average spacing of approximately 90 nm. The wall thickness of the hematite nanotubes was of approximately 30 nm. A comparative study of the photoelectrochemical properties
of these two different hematite nanostructures under water-splitting conditions have been studied through EIS and PEIS methods. The strong correlation between the C
SS increase with the R
SS,ct decrease and the photocurrent development as the potential is
made more anodic, indicated that holes transfer for the water splitting reaction takes place through the surface states and not directly from valence band holes. From the PEIS spectra the rate constants of the elementary reactions responsible for the competing processes of interfacial charge
transfer (k
tr and electron–hole recombination (k
rec have been determined. A better photoresponse kinetic was observed from the hematite nanotubular structure as compared to the nanoporous one. The last indicates that in the hematite nanotubular structure
it exists a very well length scale matching between the nanotube wall thickness and the hole diffusion length (maximize light absorption while maintaining the bulk within hole collection length), diminishing then the recombination processes.
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Keywords:
EIS;
Hematite;
Impedance;
Nanostructures;
Nanotubes;
PEIS;
Ultrasound-Assisted Anodization;
Water Splitting
Document Type: Research Article
Affiliations:
1:
Instituto de Química, Facultad de Ciencias, Pontificia Universidad Católica de Valparaíso, Av. Brasil, 2950, Valparaíso, Chile
2:
Escuela de Ingeniería Química, Facultad de Ingeniería, Pontificia Universidad Católica de Valparaíso, Av. Brasil, 2950, Valparaíso, Chile
3:
Laboratorio de Materiales y Superficies (Unidad Asociada al CSIC). Departamento de Física Aplicada & Ing. Química, Universidad de Málaga, E29071 Málaga, Spain
4:
Instituto de Física & CINQUIFIMA, Facultad de Ingeniería, Julio Herrera y Reissig 565, C. C. 30, 11000 Montevideo, Uruguay
Publication date:
01 July 2017
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Journal for Nanoscience and Nanotechnology (JNN) is an international and multidisciplinary peer-reviewed journal with a wide-ranging coverage, consolidating research activities in all areas of nanoscience and nanotechnology into a single and unique reference source. JNN is the first cross-disciplinary journal to publish original full research articles, rapid communications of important new scientific and technological findings, timely state-of-the-art reviews with author's photo and short biography, and current research news encompassing the fundamental and applied research in all disciplines of science, engineering and medicine.
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