Defying Thermodynamics: Stabilization of Alane Within Covalent Triazine Frameworks for Reversible Hydrogen Storage
Vitalie Stavila, Sichi Li, Chaochao Dun, Maxwell A. T. Marple, Harris E. Mason, Jonathan L. Snider, Joseph E. Reynolds, Farid El Gabaly, Joshua D. Sugar, Catalin D. Spataru, Xiaowang Zhou, Brennan Dizdar, Eric H. Majzoub, Ruchira Chatterjee, Junko Yano, Hendrik Schlomberg, Bettina V. Lotsch, Jeffrey J. Urban, Brandon C. Wood, Mark D. Allendorf
Abstract
Abstract The highly unfavorable thermodynamics of direct aluminum hydrogenation can be overcome by stabilizing alane within a nanoporous bipyridine‐functionalized covalent triazine framework (AlH 3 @CTF‐bipyridine). This material and the counterpart AlH 3 @CTF‐biphenyl rapidly desorb H 2 between 95 and 154 °C, with desorption complete at 250 °C. Sieverts measurements, 27 Al MAS NMR and 27 Al{ 1 H} REDOR experiments, and computational spectroscopy reveal that AlH 3 @CTF‐bipyridine dehydrogenation is reversible at 60 °C under 700 bar hydrogen, >10 times lower pressure than that required to hydrogenate bulk aluminum. DFT calculations and EPR measurements support an unconventional mechanism whereby strong AlH 3 binding to bipyridine results in single‐electron transfer to form AlH 2 (AlH 3 ) n clusters. The resulting size‐dependent charge redistribution alters the dehydrogenation/rehydrogenation thermochemistry, suggesting a novel strategy to enable reversibility in high‐capacity metal hydrides.