Abstract
This study explores an alternative hydrogen-pressure-mediated approach for electrochemical dehydrogenation and regeneration of lithium aluminum hydride (LiAlH$_4$). We systematically investigated the electrochemical oxidation/reduction behavior of 1 M LiAlH$_4$ in tetrahydrofuran (THF) under a 7 bar inert (Ar) and reactive (H$_2$) atmosphere. Under Ar, at electrode potentials >0.7 V vs Li, the oxidation reactions (alanate anions (AlH$_4^–$) → aluminum metal (Al$^0$)) dominate. At reductive potentials, we observed an indirect role of deposited Li in forming a more porous Al surface and its interaction with LiAlH$_4$-THF that leads to adsorbed LiH/AlH$_3$ species, resulting in increased oxidation current density. Under H$2$, 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 H$_2$ due to its inherent high catalytic activity. At the same time, Ni shows the best evidence for H$_2$ pressure-driven suppression of the AlH$_4^–$ oxidation process. Electrochemical studies in Li-based electrolytes (LiBF$_4$ and LiTFSI) confirmed the formation of LiH under moderate conditions (room temperature, RT; 7 bar of H$_2$). Pulsed chronopotentiometry, 1H NMR, and XRD analyses validated the presence of hydride species. Similarly, we observed a faster reactivity of dissolved H$_2$ with freshly deposited Al metal in an aluminum-containing ionic liquid (IL) electrolyte. However, $^{27}$Al NMR studies suggested the formation of predominantly [AlCl$_3$(OH)]− under H$_2$. Additionally, AlH$_4^–$ was unstable in the presence of the IL with excess AlCl$_3$, highlighting the challenges of finding suitable electrolytes for stabilizing AlH$_4^–$ species. This study provides fundamental insights into the feasibility of the electrochemical regeneration of LiAlH$_4$.