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GRAPHENE FOR HYDROGEN STORAGE

 

People

Fabio Beltram (Scuola Normale Superiore)

Camilla Coletti (IIT)

Stefan Heun - stefan.heun@nano.cnr.it

Abhishek Kumar (Scuola Normale Superiore)

Vittorio Pellegrini (IIT-CNR)

Vincenzo Piazza (IIT)

Pasqualantonio Pingue (Scuola Normale Superiore)

Stefano Veronesi

Tommaso Cavallucci (Scuola Normale Superiore)

Khatuna Kakhiani

Vito Dario Camiola

Valentina Tozzini

 


The realization of innovative hydrogen storage materials has worldwide strategic importance. In this context, graphene has recently attracted attention as a promising hydrogen storage medium. Indeed, graphene is lightweight, chemically stable, and exhibits attractive physico-chemical properties for hydrogen adsorption. Furthermore, the interaction between hydrogen and graphene can be controlled by chemical functionalization of the material, thus enabling fine tuning of the adsorption/desorption-properties of hydrogen on graphene. However, experimental demonstrations of graphene-based hydrogen storage devices have yet to be reported.

The energetics of the chemisorption of hydrogen on graphene can be modified by the local curvature of the graphene sheet. Based on scanning tunneling microscopy (STM) techniques, we demonstrated site-selective adsorption of atomic hydrogen on convexly warped regions of monolayer graphene grown on SiC(0001). This system exhibits an intrinsic curvature owing to the interaction with the substrate. We found that at low coverage hydrogen is preferentially adsorbed on convex areas of the graphene lattice (see fig. 1). No hydrogen is detected on concave regions. These findings are in agreement with our theoretical findings (based on DFT) which suggest that both binding energy and adsorption barrier can be tuned by controlling the local curvature of the graphene lattice. This curvature-dependence combined with the known graphene flexibility may be exploited for storage and controlled release of hydrogen at room temperature.

 

 

        

Fig 1: Atomically resolved STM image of graphene after exposure to atomic hydrogen for 5 seconds resulting in a low coverage of hydrogen. A diamond indicating the quasi-(6x6) superstructure is also shown. The image shows an increase in corrugation due to the C-H bonds on the convex areas of the graphene surface. Bias = 50mV and tunneling current = 0.3nA. Image obtained at room temperature.

 

 

Theoretical studies regarding metal atoms (e.g. Ti) deposited on graphene suggest that such materials can adsorb up to 8 wt% gravimetric density of hydrogen. We investigate the deposition of titanium on graphene and its potential for hydrogen storage. The growth of Ti on graphene is studied by STM. At room temperature, the titanium atoms form small islands (diameter ~ 10 nm) (see Fig.2). The hydrogen storage on these samples is studied by thermal desorption spectroscopy: the Ti-covered graphene is exposed to molecular hydrogen, and the sample temperature is then increased with a constant heating rate while measuring the mass-sensitive desorption spectrum. The desorption spectra show peaks between 200°C and 300°C. Their intensity increases with increasing Ti coverage. Our data demonstrate the stability of hydrogen binding at room temperature and show that the hydrogen desorbes at moderate temperatures in line with what is required for practical hydrogen storage applications.

 

        

Fig 2: a) 100 x 100 nm2 UHV-STM image of a graphene surface with a titanium coverage of 16% (V = 2 V, I = 280 pA). The titanium atoms form small islands with a size distribution as shown in the inset. b) Desorption spectra measured for different coverages of titanium. The amount of stored hydrogen increases with Ti-coverage.

 

This activity is performed in collaboration with the Center for Nanotechnology Innovation @ NEST of the Istituto Italiano di Tecnologia (IIT).

 

Publications

 

Hydrogen storage with titanium-functionalized graphene

T. Mashoff, M. Takamura, S. Tanabe, H. Hibino, F. Beltram, and S. Heun

Appl. Phys. Lett. 103, 013903 (2013), DOI: 10.1063/1.4812830

 

Influence of graphene curvature on hydrogen adsorption: toward hydrogen storage devices

S. Goler, C. Coletti, V. Tozzini, V. Piazza, T. Mashoff, F. Beltram, V. Pellegrini, and S. Heun

J. Phys. Chem. C 117, 11506 (2013), DOI: 10.1021/jp4017536

 

Revealing the atomic structure of the buffer layer between SiC(0001) and epitaxial graphene

S. Goler, C. Coletti, V. Piazza, P. Pingue, F. Colangelo, V. Pellegrini, K. E. Emtsev, S. Forti, U. Starke, F. Beltram, and S. Heun

Carbon 51, 249 (2013)

 

Prospects for Hydrogen Storage in Graphene

V Tozzini and V Pellegrini

Phys. Chem. Chem. Phys. 15, 80-89 (2013), DOI: 10.1039/C2CP42538F

 

Reversible hydrogen storage by controlled buckling of graphene layer

V Tozzini and V Pellegrini

J. Phys. Chem. C 115, 25523 (2011), DOI: 10.1021/jp208262r


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