Hydrogen Absorption Properties of Metal-Ethylene Complexes

Wei Zhou, Taner Yildirim, Engin Durgun, and Salim Ciraci

Storing hydrogen effectively is important for fuel-cell related applications. From first-principle calculations, we predict that a single ethylene molecule can form stable complexes with light transition metals (TM) such as Ti and the resulting TM_n-ethylene complex can absorb up to ~12 and 14 wt % hydrogen for n=1 and 2, respectively. For light metals such as Li, the ethylene molecule is able to complex with two Li atoms which then binds up to two H₂ molecules per Li with absorption capacity of 16 wt %, a record high value reported so far. The stability of the proposed metal-ethylene complexes was tested by extensive calculations such as normal-mode analysis, finite temperature first-principles molecular dynamics simulations, and reaction path calculations. The phonon and MD simulations indicate that the proposed structures are very stable up to 500 K. The reaction path calculations indicate about a 1 eV activation barrier for the TM₂-ethylene complex to transform into a possible lower energy configuration where the ethylene molecule is dissociated. Importantly, no matter which isometric configuration the TM₂-ethylene complex possesses, the TM atoms are always not saturated and therefore able to bind multiple hydrogen molecules with suitable binding energy for room temperature storage. These results suggest that co-deposition of ethylene with a suitable precursor of TM or Li into nanopores of light-weight host materials may be a very promising route to discovering new materials with high-capacity hydrogen absorption properties.

 Author Information

            Name:                           Wei Zhou

            Mentor’s name:            Taner Yildirim

            Division:                       NIST Center for Neutron Research

            Laboratory:                   Materials Science and Engineering Laboratory

            Building:                       235

            Room:                           E17

            Mail Stop:                     8562

            Telephone #:                 301-975-8169

            Fax #:                            301-921-9847

            Email:                            wzhou@nist.gov

            Sigma Xi:                      full member

            Category:                       Materials Science