The removal of heavy metal cations from wastewater is a major environmental and recycling problem. Today this requires the use of asborbents able to uptake s many cations as possible, in order to reach a high purifying efficiency. Carbon based materials, such as graphene-based foams or ionic exchanges resins, have been proposed, and indeed some of them reach unprecedented efficiency - up to 300 wt. % of metal cations removal by a graphne oxide foam composite for example. The trapped cations subsequently have to be released in another solution of used water and, in the end, precipitate as solid wastes and most often stored as toxic garbages in specific places.

In this proeject, we propose to take advantage of cation loaded carbon foams or resins, and recycle/make se of them to prepare high capacity electrodes for energy storage devices operated in various electrolytes, fromaqueous media to ionic liquids. By shrewdly combining the cations trapped in the absorbent, full cells can be assembled with high energy/high power using recycled absorbent as electrodes for various devices, from metal-ion batteries to supercapacitors. This is a unique approach which has not been reported before and which combines two main problems of our society: water purification and waste recovery to be used in energy storage devices.

The synthesis and inverstigations of absorbents will be performed under the supervision of Dr. O. Crosnier and Prof T. Brousse, both experts in materials chemistry and electrochemistry applied to energy storage devices at Institut des Matériaux Jean Rouxel (IMN), Nantes. The absorbents synthesis will be performed using up-to-date literature data in the field and their compositions will be tailored in order to fit the requirements to be used as electrodes. Cations removal experiments will be conducted in order to determine uptake kinectics. Electrochemical investigators of the electrode thus prepared will be performed using advanced techniques such as in-situ and operando UV-visible spectroscopy and X-ray absorption spectroscopy. Further, the charge storage mechanism will be investigated with respect to cation dissolution into the electrolytes employed, which would decrease the cycling efficiency of the electrode. The latter will be more specifically investigated during a 6 months secondments at Chalmers University of Technology, Göteborg, SWEDEN under the supervision of Prof. Patrik Johansson. Operando confocal Raman spectroscopy focused above the surface of the electrode will be one approach to elucidate the phenomena responsible. Pending on results and interests the PhD Student will also be exposed to modelling of the solubility by e.g. DFT+COSMO-RS approaches.

A screening of the best electrodes showing the highest performance in termns of energy and power densities as well as cycling ability will be made in order to assemble the full cells which will validate the scientific approach proposed in this topic. After optimizing cell design, it is expected such device can be implemented in stationary energy storage plants that can be coupled with waste water treatment units.

Supervisor(s) contact: BROUSSE Thierry, thierry.brousse@univ-nantes.fr