Promoting Catalytic Performance of Metal Hydrides for Reversible Hydrogen Storage in N-ethylcarbazole by Electronic Structure and Hydrogen Chemical Potential Tuning

Metal hydrides are useful hydrogenation/dehydrogenation catalysts due to their reversible hydrogen absorption and desorption properties, especially in important energy-related reactions. However, the relationship between the structure of metal hydrides and their catalytic performance is still elusive. In this work, the critical role of electronic structure and H chemical potential of metal hydrides in catalysis is demonstrated by Al substitution of the classic hydrogen storage alloy LaNi₅. Theoretical calculations reveal that electron transfer from Al to Ni reduces the adsorption energy of the partially hydrogenated intermediates and leads to lower reaction barriers. Al substitution also reduces the H chemical potential of LaNi₅ and increases the availability of bulk-H in the catalytic process. The bulk-H serves as an extra hydrogen source for hydrogenation and facilitates the formation of H₂ in dehydrogenation. Thus, the chemically synthesized LaNi_4.5Al_0.5 nanoparticles exhibit considerable bifunctional catalytic performance for the hydrogenation and dehydrogenation of carbazole-type liquid organic hydrogen carriers.