H2 Adsorption and Storage on Ni4 Cluster Embedded in Multivacancy Defected Graphene. A DFT and Thermodynamic study.

AMBRUSI, R.E.; MORELLI A.G.; ORAZI, V.; MARCHETTI, J.M.; JUAN, A.; PRONSATO M.E.

La Plata

Workshop; IX Workshop on Novel Methods for Electronic Structure Calculations (IX WNMESC).; 2021

Universidad Nacional de La Plata

Carbon materials such as graphene can efficiently storagehydrogen only at cryogenic temperatures since hydrogen molecules weaklyphysisorb on the surface [1]. Decorating graphene with transition metals trappedby defects increases considerably the storage capacity reinforcing the bondingand also by the spillover process [2,3]. In the present work, calculations based on densityfunctional theory were performed to study the hydrogen adsorption and storageon Ni4 cluster embedded in defected graphene with three, four andsix vacancies (D2h and D6h symmetry). The Gibbs freeenergy change with temperature was obtained according to statistical mechanicsthrough a canonical ensemble approach. Based on the adsorption energies and bond distances,the first H2 molecule dissociates in all the systems except H2/Ni4@V4.Energy absorption of a second and a third H2 molecule ranges between-0.3 and -0.7 eV with a 0.8-0.9 Å H-H bond distance, corresponding to aphysico-chemical mechanism. The 4th molecule adsorbed has a purelyphysical interaction with the surface (0.1 eV). The stability analysis with thetemperature suggests that the second molecule for H2/Ni4@V3and H2/Ni4@V6_D2h systems canbe desorbed at temperatures close to 298 K, suitable for hydrogen reversibleadsorption-desorption at ambient conditions. A stable dissociative adsorptionup to more than 600 K promises a hydrogen storage efficiency improvement byspillover, which occurs at lower temperatures.  References: [1]       Y. Yürüm, A.Taralp, and T. N. Veziroglu, Int. J. Hydrogen Energy, 34 (2009) 3784.[2]       J. W. Lee, H. S. Kim, J. Y.Lee, and J. K. Kang, Appl. Phys. Lett. 88 (2006) 6.[3]       L. Chen, A. C. Cooper, G.P. Pez, and H. Cheng, J. Phys. Chem. C 111 (2007) 18995.