|Thesis supervisor : ||
Gheorghe Sorin Chiuzbaian
Université Sorbonne, Université Pierre et Marie Curie - Laboratoire de Chimie Physique Matière et Rayonnement
+33 1 44 27 66 15
Personal web page : http://iramis.cea.fr/Pisp/dana.stanescu/
Hydrogen production by water splitting is a clean and viable approach, but it is very greedy in electrical energy. To reduce the energy input we study the possibility of using solar radiation. Absorbed by identified and optimized semiconducting oxides, solar radiation generates electron-hole pairs that will participate in the redox reactions in a solar water splitting process1,2.
Hematite is the prototypical semiconductor material used as a photoanode. Hematite is very abundant, not expensive and with low environmental impact, assets that should be considered with particular attention nowadays. Significant progress has been made to improve the properties of hematite for a more efficient photoelectrolysis reaction2–5. Nevertheless, compared with materials with higher efficiencies6, hematite appears to be less effective due to the reduced holes mean free path2 and to the poor kinetics at the hematite / electrolyte interface during the oxidation7,8. The existence of surface states prevents a direct transfer of the holes in the electrolyte during the water oxidation9. Optimizing surface kinetics by controlling these surface states is therefore the key for hematite efficiency increasing when it is used as photoanode10.
We propose a study aiming at understanding and optimizing the surface kinetics and the time stability of hematite-based photoanodes, at both macro and nano-meter scales and under real working conditions, i.e. during the photoelectrochemical reaction. The hematite nanowires will be deposited by aqueous chemical growth (ACG11). Different surface treatments (ionic abrasion, chemical etching, annealing, surface functionalization, etc.) will be tested and analyzed to improve surface kinetics. Combining scanning transmission X-ray microscopy (STXM) and electron microscopy (TEM12 and ESEM13,14), in operando, using a dedicated electrochemical cell containing hematite nanowires as working electrode, will allow us to determine the chemical composition and the electronic structure at the nanoscale, during the oxidation. This approach will highlight and quantify the surface states responsible for the low OER kinetics of the hematite. Microscopy results will be correlated with the photoelectrochemical activity of photoanodes measured on dedicated photocurrent setup, the surface morphology will be measured by atomic force microscopy (AFM) and SEM and the surface potential measured by Kelvin Probe Force Microscopy (KPFM). In the end, this study should provide specific solutions to improve the efficiency of hematite-based photoanodes for solar water splitting.
1. Fujishima, A. & Honda, K. Nature 238, 37–38 (1972).
2. Krol, R. va de & Grätzel, M. (Springer, 2012).
3. Rioult, M., Magnan, H., Stanescu, D. & Barbier, A. J. Phys. Chem. C 118, (2014).
4. Rioult, M., Stanescu, D., Fonda, E., Barbier, A. & Magnan, H. J. Phys. Chem. C 120, 7482–7490 (2016).
5. Rioult, M., Belkhou, R., Magnan, H., Stanescu, D., Stanescu, S., Maccherozzi, F., Rountree, C. & Barbier, A. Surf. Sci. 641, 310–313 (2015).
6. Kalanoor, B. S., Seo, H. & Kalanur, S. S. Mater. Sci. Energy Technol. 1, 49–62 (2018).
7. Tamirat, A. G., Rick, J., Dubale, A. A., Su, W. N. & Hwang, B. J. Nanoscale Horizons vol. 1 243–267 (2016).
8. Glasscock, J. A., Barnes, P. R. F., Plumb, I. C. & Savvides, N. J. Phys. Chem. C 111, 16477–16488 (2007).
9. Iandolo, B., Wickman, B., Zoric, I. & Hellman, A. J. Mater. Chem. A 3, 16896–16912 (2015).
10. Zhang, J. & Eslava, S. Sustainable Energy and Fuels vol. 3 1351–1364 (2019).
11. Vayssieres, L. International Journal of Nanotechnology vol. 1 1–41 (2004).
12. Ortiz Peña, N., Ihiawakrim, D., Han, M., Lassalle-Kaiser, B., Carenco, S., Sanchez, C., Laberty-Robert, C., Portehault, D. & Ersen, O. ACS Nano 13, 11372–11381 (2019).