Hydrogen Absorption Properties of Metal-Ethylene Complexes

Recently, we have predicted [Phys. Rev. Lett. 97, 226102 (2006)] that a single ethylene molecule can form stable complexes with light transition metals (TMs) such as Ti and the resulting TMn-ethylene complex can absorb up to ~ 12 and 14 wt % hydrogen for n=1 and 2, respectively. Here we extend this study to include a large number of other metals and different isomeric structures. We obtained interesting results for light metals such as Li. The ethylene molecule is able to complex with two Li atoms with a binding energy of 0.7 eV/Li which then binds up to two H2 molecules per Li with a binding energy of 0.24 eV/H2 and 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 firstprinciples moleculardynamics (MD) simulations, and reaction path calculations. The phonon and MD simulations indicate that the proposed structures are stable up to 500 K. The reaction path calculations indicate about 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 able to bind multiple hydrogen molecules with suitable binding energy for room-temperature storage. These results suggest that codeposition 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. Disciplines Engineering | Materials Science and Engineering Comments Suggested Citation: W. Zhou, T. Yildirim, E. Durgum and S. Ciraci. (2007). Hydrogen absorption properties of metal-ethylene complexes. Physical Review B 76, 085434. © 2007 The American Physical Society http://dx.doi.org/10.1003/PhysRevB.76.085432 This journal article is available at ScholarlyCommons: http://repository.upenn.edu/mse_papers/203 Hydrogen absorption properties of metal-ethylene complexes W. Zhou,1,2 T. Yildirim,1,2,* E. Durgun,3,4 and S. Ciraci3,4 1NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA 2Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA 3Department of Physics, Bilkent University, Ankara 06800, Turkey 4UNAM-National Nanotechnology Research Center, Bilkent University, Ankara 06800, Turkey Received 23 January 2007; revised manuscript received 6 March 2007; published 30 August 2007 Recently, we have predicted Phys. Rev. Lett. 97, 226102 2006 that a single ethylene molecule can form stable complexes with light transition metals TMs such as Ti and the resulting TMn-ethylene complex can absorb up to 12 and 14 wt % hydrogen for n=1 and 2, respectively. Here we extend this study to include a large number of other metals and different isomeric structures. We obtained interesting results for light metals such as Li. The ethylene molecule is able to complex with two Li atoms with a binding energy of 0.7 eV/Li which then binds up to two H2 molecules per Li with a binding energy of 0.24 eV/H2 and 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 moleculardynamics MD simulations, and reaction path calculations. The phonon and MD simulations indicate that the proposed structures are stable up to 500 K. The reaction path calculations indicate about 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 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. DOI: 10.1103/PhysRevB.76.085434 PACS number s : 68.43.Bc, 81.07. b, 84.60.Ve