Fluorinated materials for the production of decarbonated NH3
Résumé
Achieving carbon neutrality by 2050 is an ambitious yet crucial goal to counteract climate change. Ammonia (NH3) emerges as a complementary vector to hydrogen (H2) in achieving this neutrality as an alternative to fossil fuels. Indeed, this molecule chemically stores energy and can release it in the form of H2 through simple heating, earning it the designation of nitrogenated hydrogen. Its combustion without CO2 emissions and its energy density, twice that of hydrogen, make ammonia an ideal substitute fuel for decarbonization, particularly in maritime and aviation transport, replacing heavy fuel oil and kerosene. To make its production sustainable, electrolysis of nitrates (NO3-) presents a virtuous solution compared to the current industrially intensive and polluting Haber-Bosch process, while also purifying nitrate-laden waters. To make this reduction of NO3- ions into NH3 (NO3-RR) viable, the development of more efficient electrocatalysts is required. The team at Le Mans recently demonstrated that a copper and aluminum-based oxyfluoride, Cu3Al2OF10, prepared by thermal treatment of the precursor Cu3Al2F12(H2O)12, outperformed reference materials. While the selectivity of this material remains improvable, these results demonstrate that oxyfluorides are real candidates for the production of decarbonized NH3. My research aims to explore new copper-based oxyfluoride materials and evaluate their electrochemical properties to improve NH3 production selectivity and efficiency. Identifying optimal chemical compositions favoring abundant and non-toxic metals such as copper and iron will be considered to enhance electrocatalytic performance, especially in terms of selectivity. Thus, through substitutions, several series of new solid solution formulations M+II1-xCuxAlF5(H2O)7 (M+II = Ni, Co) and Cu3-xM+IIxM+III2F12(H2O)12 with (M+II = Co, Ni and M+III = Al, Fe) will be presented. My contribution will focus on the synthesis and structural characterization of these new materials with a preliminary evaluation of their electrochemical properties. Références [1] Valera-Medina, A. et al. (2021). Review on ammonia as a potential fuel: From synthesis to economics. Energy and Fuels. DOI: 10.1021/ACS.ENERGYFUELS.0C03685. [2] Guiet, A. et al. (2023). Reversible transition of an amorphous Cu-Al oxyfluoride into a highly active electrocatalyst for nitrate reduction to ammonia. Chem. Catalysis. DOI: https://doi.org/10.1016/j.checat.2023.100595.
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