Remarkable enhancement in hydrogen storage on free-standing Ti3B and BC3 supported Ti3 clusters

Abstract

Hydrogen storage capacity of Tin−1B (n = 3–7) clusters is studied and compared with that of the pristine Tin (n = 3–7), using density functional theory (DFT) based calculations. Among these clusters, Ti3B shows the most significant enhancement in the storage capacity by adsorbing 12 H2, out of which three are dissociated and the other nine are stored as di-hydrogen via Kubas-interaction. The best storage in Ti3B is owed to a large charge transfer from Ti to B along with the largest distance of Ti empty d-states above the Fermi level, which is a distinct feature of this particular cluster. Furthermore, the effect of substrates on the storage capacity of Ti3B was assessed by calculating the number of adsorbed H2 on Ti3 cluster anchored onto B atoms in the B-doped graphene, BC3, and BN substrates. Similar to free-standing Ti3B, Ti3 anchored onto boron atom in BC3, stores nine di-hydrogen via Kubas interaction, at the same time eliminating the total number of non-useful dissociated hydrogen. Gibbs energy of adsorption as a function of H2 partial pressure, indicated that at 250 K and 300 K the di-hydrogens on Ti3@BC3 adsorb and desorb at ambient pressures. Importantly, Ti3@BC3 avoids the clustering, hence meeting the criteria for efficient and reversible hydrogen storage media.