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Surface-Functionalized Nanoporous Carbons for Kinetically Stabilized Complex Hydrides through Lewis Acid–Lewis Base Chemistry

2016; American Chemical Society; Volume: 120; Issue: 21 Linguagem: Inglês

10.1021/acs.jpcc.6b03374

1932-7455

Christopher L. Carr, Eric H. Majzoub,

Catalysis and Hydrodesulfurization Studies

Complex metal hydrides are an attractive hydrogen storage option due to their high gravimetric hydrogen capacities, but the re/dehydriding reactions generally possess unfavorable thermodynamics and kinetics. Recent studies have attempted to alter these properties through confinement of complex hydrides in nanoporous substrates. For example, LiBH4 may be melt-infiltrated into a nanoporous carbon (LiBH4@NPC), where electron-withdrawing boron concomitantly incorporates into the substrate, facilitating the wetting of the pores with molten LiBH4. We present results of the surface functionality displayed by incorporation of electron-donating nitrogen into a nanoporous carbon. The presence of pyridinic nitrogen in the substrate, confirmed by XPS analysis, acts as a Lewis base. Our results indicate partial decomposition on melt-infiltration of LiBH4 may produce electron-accepting BH3 defects at the surface of the hydride forming a stabilizing capping layer. Isothermal hydrogen desorption measurements indicate an activation energy increase of greater than 30 kJ/mol for LiBH4 confined in N-doped versus undoped substrates. Further, temperature-programmed desorption (TPD) measurements show a temperature increase of over 25 °C in the diborane (B2H6) signature, marking the beginning of the dehydriding reaction. Stabilizing metal hydrides kinetically through the formation of a capping layer induced by substrate functionalities may allow the use of a wide class of unstable complex metal hydrides with enthalpies below 15 kJ/mol H2, such as AlH3, in hydrogen storage systems.