Functionalized graphene as a system for hydrogen storage
T. Mashoff1, M. Takamura2, S. Tanabe2, H. Hibino2, D. Convertino1, V. Miseikis1, C. Coletti1, V. Piazza1, F.
Beltram1,3, and S. Heun3
1
Center for Nanotechnology Innovations @NEST, Istituto Italiano di Tecnologia, 56127 Pisa, Italy
2 NTT Basic Research Laboratories, NTT Corporation, 3-1, Morinosato Wakamiya, Atsugi,
Kanagawa 243-0198, Japan
3 NEST, Istituto Nanoscienze – CNR and Scuola Normale Superiore, Piazza San Silvestro 12, Pisa, Italy
(Torge.Mashoff@iit.it)
Hydrogen is well known as a possible clean fuel for the future since the only waste product is water.
Nevertheless, one of the main problems dealing with hydrogen as a widespread energy carrier is its storage. In
this respect, graphene has recently attracted attention as a promising medium due to its small weight, chemical
stability, and attractive physico-chemical properties for hydrogen adsorption. The hydrogen storage capacity of
graphene can be further increased by chemical functionalization of the surface with different types of metals.
One of the most promising materials for this purpose is titanium. Calculations show that each adsorbed titanium
atom can bind up to 4 ~ 5 H2 molecules, with related gravimetric density of 7.8 wt% [1]. In this work, we
investigated the deposition of titanium on graphene and its potential for hydrogen storage.
For this study we used epitaxial monolayer graphene grown on SiC(0001). Different quantities of titanium were
deposited on this surface. The characteristics of the growth process and the amount of coverage were
determined by scanning tunneling microscopy (STM) in ultra high vacuum (UHV). As shown in Fig. 1a, the
titanium atoms form small islands (diameter ~ 10 nm) with a size distribution given in the inset. The Ti-covered
graphene was exposed to molecular hydrogen (5 min at 1x10 -7 mbar deuterium). The sample temperature was
then increased up to 550 ºC with a constant heating rate of 10 K/s while measuring the mass-sensitive
desorption. The desorption spectra are shown in Fig. 1b. Two desorption peaks at 210 ºC and 290 ºC are clearly
visible. Their intensity increases with increasing Ti coverage [2]. We verified that without Ti there was no
desorption detectable. Our data demonstrate suitability of functionalized graphene for hydrogen storage
applications, since the binding is stable at room temperature and desorption occurs at moderate temperatures.
Table5_3
Dataset : Table5_3
Functi on : y0+A*sqrt(2/PI)/w*exp(-2*((x-xc)/w)^2)
Chi ^2 / doF = 8.9157748105736e+01
R ^2 = 0.7843133109686
A = 2.4363974700307e+02 +/- 4.3251474826526e+01
x c = 7.8574700158818e+00 +/- 2.9489889631448e-01
w = 4.0260104126567e+00 +/- 6.7349019516836e-01
y 0 = 7.9634935294571e+00 +/- 2.8805513251623e+00
To decrease the size of the Ti-islands and increase their density and therefore the active surface for hydrogen
adsorption, we will show first promising results of reducing the mobility of the titanium by defects induced in the
graphene layer by ion bombardment.
[1]
[2]
E. Durgun et al., Phys. Rev. B 77, 085405 (2008).
T. Mashoff et al., Appl. Phys. Lett. 103, 013903 (2013).
a)
b)
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Fig. 1: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 Ticoverage.