High-Pressure Electrochemical Investigation of Lithium Alanate Dehydrogenation and Regeneration Mechanisms

This study explores an alternative hydrogen-pressure-mediated approach for electrochemical dehydrogenation and regeneration of lithium aluminum hydride (LiAlH4). We systematically investigated the electrochemical oxidation/reduction behavior of 1 M LiAlH4 in tetrahydrofuran (THF) under a 7 bar inert (Ar) and reactive (H2) atmosphere. Under Ar, at electrode potentials >0.7 V vs Li, the oxidation reactions (alanate anions (AlH4–) → aluminum metal (Al0)) dominate. At reductive potentials, we observed an indirect role of deposited Li in forming a more porous Al surface and its interaction with LiAlH4-THF that leads to adsorbed LiH/AlH3 species, resulting in increased oxidation current density. Under H2, the oxidation currents decrease due to the suppression of hydrogen-releasing reactions and the passivation of the Li surface by LiH formation. Further analysis of different working electrodes (Ni, Pd, and GC) revealed that Pd performs best under Ar and H2 due to its inherent high catalytic activity. At the same time, Ni shows the best evidence for H2 pressure-driven suppression of the AlH4– oxidation process. Electrochemical studies in Li-based electrolytes (LiBF4 and LiTFSI) confirmed the formation of LiH under moderate conditions (room temperature, RT; 7 bar of H2). Pulsed chronopotentiometry, 1H NMR, and XRD analyses validated the presence of hydride species. Similarly, we observed a faster reactivity of dissolved H2 with freshly deposited Al metal in an aluminum-containing ionic liquid (IL) electrolyte. However, 27Al NMR studies suggested the formation of predominantly [AlCl3(OH)]− under H2. Additionally, AlH4– was unstable in the presence of the IL with excess AlCl3, highlighting the challenges of finding suitable electrolytes for stabilizing AlH4– species. This study provides fundamental insights into the feasibility of the electrochemical regeneration of LiAlH4.