Gallium as a liquid phase to improve the reversibility of nanoconfined LiBH4

IGNACIO ARIEL GARANZINI; PIERRE ARNEODO LAROCHETTE; AURELIEN GASNIER

Buenos Aires

Congreso; WCCE11 - 11th WORLD CONGRESS OF CHEMICAL ENGINEERING; 2023

AAIQ Asociacion Argentina de Ingenerios Quimicos

The combustion of fossil fuels remains a primordial source of energy, despite their finitude and environmental impact. While “green” energies exist, their production is intermittent and random, hindering their implementation into the current energy matrix. Using hydrogen as an energy reservoir could buffer the temporal dephasing between supply and demand. Yet, storing large amounts of compressed/liquefied H2 isn´t optimal (volume, energy, safety).Our group focuses on hydrides (particularly LiBH4) as a source of H2, because the stability of the metal-H bound solves many of these issues. Whereas its gravimetric content is high (13,6 wt.%), the liberation of H2 requires high temperatures (Td~500 ºC) to overstep the thermodynamics and kinetics barriers of the reaction (LiBH4 (l) ⇌ LiH (s) + B (s) + 3/2 H2 (g)). We and others have proposed several strategies to break this bottleneck, especially the nanoconfinement of the hydride within a mesoporous carbon matrix (Cmeso).[1] The temperature of H2 release/capture was lowered, but the reversibility of the system still needed to be improved (typically, only 6-7 wt. % of H2 is released after the first cycle). Indeed, the rehydrogenation process involves three species that tend to segregate: as B accommodates within the carbon vacancies of the pore, LiH ejects at the pore mouth.[2]To promote the encounter of LiH with B, we proposed a liquid medium to enhance their mobility and improve the reversibility of the system. We know no such approach in the literature on the topic. In this study, we employ gallium (Tf~30 ºC) as the liquid medium, given its low vapor pressure even at high temperatures. Based on nitrogen isotherms, we will present the impact of Ga manual grinding over the porosity of Cmeso, and how Ga affected LiBH4/LiH pore filling. We studied the cryoscopic descent of Ga in Cmeso (Tf~-15 ºC) and its impact over nanoconfined LiBH4 (Td~315 ºC) by Differential Scanning Calorimetry. Scanning Electron Microscopy of Ga@Cmeso illustrated complications in the homogeneous repartition of Ga over Cmeso. The morphological and chemical evolution of hydrides, borides, and metals was evaluated by X-Ray Diffraction before/after LiBH4 decomposition. The operational temperature, hydrogen capacity, and reversibility of the system were evaluated by volumetric studies.