Description of the thesis topic

Full title. Which inorganic molecules to mimic the energy conversion capacity of solids ? Molybdenum clusters for photovoltaics and electrolytic water splitting.

Key words. solution chemistry, inorganic chemistry, solid-state chemistry, materials chemistry, metal clusters, photovoltaics, electrocatalysis, hydrogen evolution reaction.

Context. As human societies face climate challenges, it is necessary to develop sober and efficient technologies in order to meet energy needs. Sobriety implies, amongst other criteria, the use of resources which have the lesser impact, notably among the metals. Efficiency reflects the highest possible energy production capacity per atom. Thanks to their size and geometry, metal clusters represent the smallest units of inorganic solids which are active as photovoltaic cell sensitizers and catalysts for the formation of H2 from H2O. Metal clusters are molecules with a finite number of metal atoms, linked together necessarily but not exclusively with metal-metal bonds. The Team Solid State Chemistry and Materials at the ISCR recently developed a promising strategy to obtain metal clusters (Figure 1*) with their photoactivity which could be modulated by their composition, size and geometry.

Scientific locks. The main challenge is to elaborate a new synthetic pathway to access inorganic cluster-containing compounds with high purity and maximal quantities. This is of upmost importance to then pursue investigations of their photophysical and electrochemical properties, and their integration in functional devices. The stabilisation of sulphurated molecular clusters is a key milestone before associating them with Mo6Cl142- and study the generation of electron and holes in photovoltaic cells. Furthermore, a fundamental challenge of the project is isolate Mo clusters with an interstitial boron atom (BMo6) and with an analogous geometry compared to MoB2. Once stabilized, they will be evaluated as catalysts of the hydrogen evolution reaction, and then compared to bulk MoB2.

* Figures et references
https://drive.google.com/file/d/1kb2BdJEpuznkiwLUFuLKx8J60Yp1Wma4/view?usp=sharing

Work Context

Approach and Methods. The exploration of the new molybdenum cluster compounds will be based on an in-solution synthetic pathway, in inorganic molten salts. For example, an equimolar mix of NaCl and AlCl3 melts at 105 °C, and then is stable beyond 400 °C. This type of solvent has been proved adequate to obtain a diversity of nanocrystals, especially metal borides. Pionnering works from the 1970s have demonstrated the possibility to obtain molybdenum halogenide clusters Mo6Cl142-. Up to now, no one further studied how to adapt the approach towards species comprising other inorganic ligands consisting in elements from the block p. The PhD project aims at diversifying the compositions, geometries and nuclearities of metal clusters, by associating them with exotic ligands (Figure 2). Depending on their optical and electronic properties, these new molecules will be investigated for the production of electric energy in photovoltaics, or chemical energy in the form of H2 formed by water electrolysis. The work will be jointly performed by the PhD students and collaborators implied in the project.

PhD environment. The PhD student will be accompanied to conduct an ambitious project in the field of Solid-State Chemistry, aiming at materials for the conversion of energy. Her/His/Their work will pass through dedicated trainings and formations to acquire skills for the management of a project, for team work, for the communication of results, as well as technical know-how to perform Chemistry research: syntheses in inorganic molten salts, comprising handling in inert atmosphere (glovebox, Schlenk line); characterization techniques comprising but not limited to structural resolution by X-Ray diffraction, X-ray photoemission, electron microscopy, and Raman spectroscopy; and photovoltaic and electrocatalytic assessments, including device preparation, data measurement and analysis. The person will work three years in a collaborative project, which could include stays in laboratories abroad (Belgium, Italy, United States). He/She/They will be central in building and sharing knowledge produced by the team working on the project. The person engaged will become a specialist in the field and an expert to be consulted and to guide the search for new cluster compounds.

* Figures et references
https://drive.google.com/file/d/1kb2BdJEpuznkiwLUFuLKx8J60Yp1Wma4/view?usp=sharing

The position is located in a sector under the protection of scientific and technical potential (PPST), and therefore requires, in accordance with the regulations, that your arrival is authorized by the competent authority of the MESR.