Boranes, hydrures complexes vecteurs d’hydrogène: stockage, hydrolyse et synthèse par recyclage – BoraHCx

The present energy and environment context is rather favourable to the development of alternate and/or new energies, like hydrogen. Nevertheless the issue regarding its storage hinders the development of a hydrogen economy. Today several storage solutions have been envisaged. Among the most promising ones, one can distinguish the boron hydrides like ammoniaborane NH3BH3. This compound is composed of 19.6 wt% of hydrogen, what is one of the highest gravimetric hydrogen storage capacities. However at our knowledge NH3BH3 is not investigated in France. In such a context we have started preliminary tests for studying the real capacities of this material and the preliminary experimental results are quite promising. Hence in the framework of this project ANR Jeunes Chercheurs, we propose developing our research activity around this hydrogen storage material and we propose positioning us (laboratory, university and nation) in the worldwide research devoted to hydrogen. We propose studying NH3BH3 with fundamental and applied objectives. We will investigate in details its hydrogen storage capacities and its hydrogen generation abilities. The dehydrogenation reaction we choose is the catalysed hydrolysis. The present project has several scientific and technical objectives. Due to the fact that NH3BH3 is one of the most promising boron hydrides and because the research area devoted to this complex is just emerging, the fundamental aspects have not been investigated in details yet. Therefore there is a rather large research area that still needs to be explored: - Reaction mechanisms, - Nature and in-situ evolution of the reaction intermediates, - Nature and in-situ evolution of the metal-based catalyst surface active sites, - Kinetics (activation energy over a large range of temperature, reaction orders for several temperatures over the same range of temperature) and kinetic modelling. - Nature of the hydrolysis by-products. For this fundamental study, a model catalyst will be chosen (after a first screening prior to the present project). This study will be the task 1. The task 2 will be completely dependent on the task 1. Information obtained through this task 1 will give answers about the hydrolysis reaction and this knowledge should permit to begin a more applied research (tasks 2 and 3), which will have the following objectives: - Searching for efficient, reactive, selective metal-based catalysts while focusing on metals cheaper (e.g. Co, Ni...) than the noble metals (Ru, Pt, Rh...), - Optimisation of the metal-based catalyst in order that it is durable in operating conditions, - Preparation of shaped catalyst with the viewpoint of a technological application (this sub-task will be dependent on the final choice of the storage solution optimised in the task 3), - Full characterisation of the catalyst, prior and after tests. These are the objectives of the task 2. The task 3 will have the following objective: - Optimisation of the gravimetric hydrogen storage capacity of the system NH3BH3-H2O, either by reducing the amount of water towards stoichiometric proportions or thinking the utilisation of NH3BH3 differently (solid, gel and so on). The first three tasks will be achieved in the framework of a PhD thesis for which a grant is asked to the ANR through the present project. The thesis will be divided into three years, each year being devoted to one task. The tasks 2 and 3 will be rather independent but they will have the final objective to propose a lab-scale prototype. This prototype will integrate the best shaped catalyst and the optimised hydrogen storage solution. Finally studies for synthesising NH3BH3 will be initiated. Note that the synthesis will be achieved from the hydrolysis by-products. This is the task 4. The objectives will be as follows: - Recycling of the by-products stem from the hydrolysis back into NH3BH3 or into another boranes like e.g. LiNH2BH3 or NH3B3H7, - Hydrolysis and thermolysis of the recycled NH3BH3 (or hydrides). A post-doctorate fellow will be recruited for this task 4. Hence a grant will be asked to the ANR. In conclusion five young researchers and two young PhD and post-doctorate researchers will be involved in the present project. Furthermore we will mainly use our existing set-ups. We will thus valorise our test benches currently used for the hydrolysis of NaBH4. Finally, our main forces will be our skills complementary, our experience in boron chemistry and our experience in hydrogen storage through the boron hydride NaBH4 (as well as its catalysed hydrolysis).