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Nanostructured hematite photoanodes optimisation by Ti doping for hydrogen production by solar water splitting

Contact: STANESCU Dana, , dana.stanescu@cea.fr, +33 1 69 08 75 48
Summary:
Correlative study between the macroscopic hydrogen production efficiency for different Ti doping levels of hematite photoanodes obtained by aqueous chemical growth and the local chemical/structural/electronic properties of the photoanodes.
Possibility of continuation in PhD: Oui
Deadline for application:30/04/2019

Full description:
M2 internship (Synchrotron SOLEIL / SPEC)
Responsible SOLEIL: Stefan Stanescu (stefan.stanescu@synchrotron-soleil.fr)
Responsible CEA: Dana Stanescu (dana.stanescu@cea.fr)

Renewable energy sources, only 20% of the present mankind’s global energy consumption, will constitute a reliable answer to the energy demand if they reduce carbon dioxide emissions into the atmosphere. Hydrogen appears to be an efficient and sustainable energy carrier since its specific energy is around 120 MJ/Kg, higher than in hydrocarbons (46 MJ/Kg) or lithium air batteries (8 MJ/Kg). Nowadays, more than 95% of total hydrogen production (ca. 50 millions of tonnes per year) depends on the fossil fuels industry, mainly steam methane reforming. Therefore, the carbon impact is huge. Hydrogen can also be produced by water electrolysis. A significant energy input is however necessary to produce the voltage bias necessary to initiate redox reaction (1.23 V). A novel idea, inspired by photosynthesis, is water photoelectrolysis, where sunlight is used to reduce the voltage bias necessary to split hydrogen from water molecule [1]. In most cases, a photo electrochemical cell consists of an n-type semiconductor photoanode associated with a conventional metal cathode, the macroscopic parameter that confirms hydrogen production being the generated photocurrent.
We are currently studying pure and doped hematite photoanodes obtained using a simple and versatile method, namely the ACG: Aqueous Chemical Growth [2]. Several growth parameters like the solution pH, temperature, time allow tuning the properties of these photoanodes. In a previous study on model epitaxial films, it was demonstrated a 10 times increase in the photo-electrochemical efficiency upon hematite doping with Ti [3]. We propose here to characterize and correlate the macroscopic hydrogen production efficiency for different Ti doping levels of hematite photoanodes obtained by ACG with the local chemical/structural/electronic properties of the materials.
The intern will have several missions: a) elaboration of a protocol insuring reproducible elaboration of Ti-doped samples with precise control of the doping level; b) characterization of the hydrogen production efficiency by photocurrent measurements; c) characterization of chemical/structural/electronic properties using state of the art microscopy tools; d) evidence and model correlations between macroscopic conduction to local properties. Combined laboratory (photocurrent, SEM - Scanning Electron Microscopy, XRD - X-ray Diffraction, XPS - X-ray Photoemission Spectroscopy) and synchrotron (STXM - Scanning Transmission X-ray Microscopy, XPEEM - X-ray PhotoEmission Electron Microscopy, XAS - X-ray Absorption Spectroscopy) techniques will be used to realize this study.
The internship will take place on HERMES beamline [4] from Synchrotron SOLEIL, dedicated to X-ray microscopy (STXM and XPEEM). Photoanodes deposition and photocurrent measurements will be realized at SPEC laboratory from CEA-Saclay.

[1] A. Fujishima and K. Honda, Nature, 1972, 238, 37 (1972), 10.1038/238037a0
[2] L. Vayssieres, Int. J. Nanotechnol. 2004, 1, 10.1504/IJNT.2004.003728, L. Vayssieres, Appl. Phys. A 89, 1–8 (2007), 10.1007/s00339-007-4039-0,
[3] M. Rioult, H. Magnan, D. Stanescu, A. Barbier, J.Phys.Chem.C, 2014, 118 (6), pp 3007–3014, 10.1021/jp500290j
[4] R. Belkhou, S. Stanescu, S. Swaraj, A. Besson, M. Ledoux, M. Hajlaoui, D. Dalle, J. Synchrotron Radiat., 2015, 22 (4): 968-979, 10.1107/S1600577515007778

Technics/methods used during the internship:
synchrotron techniques: - STXM - Scanning Transmission X-ray Microscopy - XAS - X-ray Absorption Spectroscopy laboratory techniques: SEM - Scanning Electron Microscopy, XRD - X-ray Diffraction XPS - X-ray Photoemission Spectroscopy ACG - Aqueous Chemical Growth photocurrent measurements

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