Promoting Effect of Carbon Surfaces on H2 Dissociation on Aln Clusters by First Principles Calculations

Abstract

Recent experiments show that carbon nanomaterials, such as carbon nanofibers, may be used to catalyze the dehydrogenation and rehydrogenation of hydrogen storage materials, such as the benchmark complex metal hydride NaAlH4. However it is not clear how the carbon material can accomplish the dissociation (or recombination) of H2. In this work we investigate the dissociation of H2 on Aln (n = 2, 4, and 6) clusters supported by coronene and graphene substrates using density functional theory (DFT), where coronene and graphene are taken as models for nanographitic surfaces. In our calculations, we account for van der Waals interactions by adapting the correlation part of the PBE exchange-correlation functional with the Grimme and Langreth corrections, and we use NEB to calculate the minimum energy reaction path for the dissociation of H2. Analysis of the minimum barrier reaction paths and the associated dissociation barriers of H2 on Aln clusters interacting with the modeled carbon surfaces shows that the investigated carbon materials have a promoting effect on the dissociation of H2 on the Aln clusters, resulting in barrierless dissociation of H2 on Al4 and Al6 supported on coronene. The calculations on coronene suggest that the promoting effect comes from a stabilization of the singlet states of Aln.