Numerical simulation of hydrogen atom transport in thick nickel membrane using semi-empirical quantum model Bin-Hao Chen a, *, Chin-Ho Chuang b , Rajesh K. Ahluwalia c , Mu-Li Chang a a Industrial Technology Research Institute, Energy and Environment Laboratories, C600, Rm. 511, No. 8, Gongyan Rd., Liujia Shiang, Tainan County, Taiwan 734, ROC b Department of Mechanical Engineering, National Cheng Kung University, Tainan, Taiwan c Department of Nuclear Engineering, Argonne National Laboratories, Argonne, IL, USA article info Article history: Received 19 August 2009 Received in revised form 8 October 2009 Accepted 8 October 2009 Available online 3 November 2009 Keywords: Hydrogen storage Hydrogen atom transport Diffusion in solids Molecular dynamics abstract The transport characteristics of hydrogen atoms are of significant interest within the energy industry. In this study, molecular dynamics (MD) simulations based on a semi- empirical quantum model are performed to examine the diffusion of hydrogen in a dense nickel membrane. The mean square displacement (MSD) and diffusion coefficients of the nickel and hydrogen atoms are derived at various temperatures in the range of 300–1800 K. The numerical results reveal the changes which take place in the transportation mecha- nism of the hydrogen atoms as a result of a temperature-induced variation in the lattice structure. It is shown that the transport of the hydrogen atoms changes from an interstitial diffusion mechanism at temperatures lower than 1200 K to a vacancy diffusion mechanism at temperatures of 1600–1800 K as result of a change in the nickel lattice from an ordered FCC structure to an amorphous-type structure. ª 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. 1. Introduction A detailed knowledge of the microscopic mechanisms responsible for the transport of hydrogen atoms in metal hydride systems is essential in developing suitable materials for the storage of hydrogen and hydride battery. Many studies have examined the mechanical relaxation of hydrogen in hydrogenated niobium over the past thirty years or so [1–4]. Therefore, the Hydrogen diffusion coefficient in niobium has been modified by many new theories and experiments. Hydrogenated niobium is a particularly attractive platform for mechanical relaxation studies of hydrogen in metals since it possesses higher hydrogen diffusivity [4,5]. However, previous investigations into the effects of hydrogen in transforming the mechanical properties of materials have considered not only body-centered cubic (BCC), but also face-centered cubic (FCC) and hexagonal close-packed (HCP) metals; amorphous alloys, intermetallic compounds (IMCs) and quasi-crystals. For example, Goltsov et al. [6] examined the kinetics of the hydrogen-induced diffusion phase transformation of binary and pseudobinary IMCs at a temperature of 600  C and a hydrogen pressure of 16.2 kPa and showed that the IMCs decomposed more readily as the rate of ferromagnetic phase nucleation reduced. Saetre [7] performed a simulation inves- tigation into the diffusion of hydrogen within spherical particles. In the simulations, the hydrogen flux into or out of the particles was initiated by means of a phase boundary located near the surface of the particles. The results showed * Corresponding author. Tel.: þ886 66939261; fax: þ886 66939096. E-mail address: bhchen@itri.org.tw (B.-H. Chen). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he 0360-3199/$ – see front matter ª 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2009.10.023 international journal of hydrogen energy 34 (2009) 9824–9831