Hydrogen absorption properties of metal-ethylene complexes

Abstract

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 TM n -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 TM 2 -ethylene complex to transform into a possible lower energy configuration where the ethylene molecule is dissociated. Importantly, no matter which isometric configuration the TM 2 -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. Recently, we have predicted ͓Phys. Rev. Lett. 97, 226102 ͑2006͔͒ that a single ethylene molecule can form stable complexes with light transition metals ͑TMs͒ such as Ti and the resulting TM n -ethylene complex can absorb up to ϳ12 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 H 2 molecules per Li with a binding energy of 0.24 eV/ H 2 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 ͑MD͒ 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 TM 2 -ethylene complex to transform into a possible lower energy configuration where the ethylene molecule is dissociated. Importantly, no matter which isometric configuration the TM 2 -ethylene complex possesses, the TM atoms are able to bind multiple hydrogen molecules with suitable binding ...

Transition-Metal-Ethylene Complexes as High-Capacity Hydrogen-Storage Media

“…Therefore we are currently studying a large number of metals and the details will be published elsewhere [19]. Our initial results are summarized in Table I, which clearly indicates that most of the light TM atoms can be bound to ethylene and each of them can absorb up to five H 2 molecules.…”

Analyzing the efficiency of M n –(C2H4) (M = Sc, Ti, Fe, Ni; n = 1, 2) complexes as effective hydrogen storage materials

“…The stability of the aforesaid all-metal systems has been attributed to the existence of an aromaticity criterion in the metallic rings which was assessed through the rationale of nucleus independent chemical shift (NICS) [12] . Yildirim et al [13][14][15][16][17][18] along with a few other research groups [19,20] have been quite successful in establishing that the C=C bond in an ethylene molecule, C 2 H 4 , like that of fullerenes and other carbon-based nanostructures can form stable complexes with a transition metal, Titanium (Ti) and the resulting Ti n − C 2 H 4 (n = 1, 2) complex in turn can bind up to ten H 2 molecules efficiently. The interaction between the hydrogen molecules and the transition metal is worth-mentioning as it is somewhat intermediate between physical and chemical adsorption but, can best be explained from the Kubas model [21] of hydrogen binding: (η 2 -H 2 ) -metal interaction.…”

Effects of Re Addition into MgB₂ Superconductor

“…Therefore Re or Re-borides are expected to be pinning centers at 20 K at which they are normal conductors. Especially, the ReB 2 has a possibility of mechanically hard pinning centers, since it has been known as an ultra-incompressible super-hard material [11][12][13].…”

“…(Received February 27, 2013; Accepted June 13,2013) become good pinning centers on the MgB 2 grain boundaries for the penetrating magnetic flux.…”