Magnetic Moment Controlling Desorption Temperature in Hydrogen Storage: A Case of Zirconium-Doped Graphene as a High Capacity Hydrogen Storage Medium

摘要

For the first time, we predict through density functional theory that a single Zr atom attached on graphene surface can adsorb maximum of 9 H-2 molecules with average binding energy of 0.34 eV and average desorption temperature of 433 K leading to a wt % of 11, higher than the DoE's requirement of 6.S wt %.The dependency of desorption temperature (T-D) of H-2 molecule with the magnetic moment (mu) of the system was exclusively studied by formulating the empirical relation T-D = T-0 + a mu(b) (with T-0 = 399 K, a = 302.38 J(-1) T K and b = 0.5). For a system with a large magnetic moment, the charge transfer to the hydrogen molecule is higher, leading to higher desorption temperature (may be higher than prescribed limit for hydrogen storage by DoE). As the magnetic moment reduces, T-D comes into the desired window for fuel cell applications. It can be inferred from this study that controlling the magnetic character of the system through doping may be an effective way to bring T-D in to the desired window. We qualitatively and extensively demonstrate through the analysis of the partial density of states and Bader charge transfer the interaction mechanism of Zr on graphene surface and hydrogen storage capability of Zr decorated graphene. As we have used GGA exchange correlations (LDA over binds the system), checked the stability through ab initio MD simulations, computed the diffusion barrier for avoiding metal-metal clustering, and predicted that the hydrogen wt % of the system (11 wt %) comes higher than the DoE's requirement (6.5 wt %) with desorption temperature (433 K) and is very much suitable for fuel cell applications, we strongly believe that Zr-doped graphene can be tailored as a high capacity hydrogen storage device.