Hydrogen Storage Capacity of Cobalt Cluster Ions

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2024-05, Vol.128 (18), p.3516-3528
• Main Authors: Mafuné, Fumitaka, Wu, Yangkun, Yamaguchi, Masato, Kudoh, Satoshi
• Format: Article
• Language: English
• Subjects: A: Structure, Spectroscopy, and Reactivity of Molecules and Clusters
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.3c08445

The adsorption of H2 on gas-phase Co n ± (n = 5–12) clusters at 300 K and the desorption of H2 from Co n H m ± upon heating were studied experimentally by combining thermal desorption spectrometry and mass spectrometry to elucidate the hydrogen storage property of the Co clusters. Hydrogen atoms adsorbed well on Co n + (n = 5, 10–12) and Co n – (n = 5–12) at 300 K to form Co n H m ±. The atomic ratios, m/n, for Co n H m – (0.9–1.4) were higher than those for Co n H m + (0.2–1.1). According to density functional theory (DFT) calculations, the first few H2 molecules had a tendency to dissociatively adsorb onto the Co clusters. Further, the bonding nature of the H atoms was ionic, similar to the H atoms in the metallic hydrides. In contrast, H2, adsorbed molecularly, was explained in terms of σ complex formation. H2 molecules were desorbed from the clusters upon heating. The temperature dependences showed that Co n H m – released H2 at a higher temperature (700–800 K) than Co n H m + (600–700 K), suggesting that Co n – should have a higher affinity to hydrogen than Co n +. The desorption temperatures were lower than those of V n H m +, which was consistent with the fact that the adsorption energies of H2 were lower for the Co clusters than those for the V clusters. The low adsorption energies were ascribed to their large highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gaps in the Co clusters.