IOP PUBLISHING NANOTECHNOLOGY
Nanotechnology 21 (2010) 065707 (5pp) doi:10.1088/0957-4484/21/6/065707
Improvement of dehydrogenation kinetics
of LiBH
4
dispersed on modified
multi-walled carbon nanotubes
Filippo Agresti
1
, Ashish Khandelwal
1
, Giovanni Capurso
1
,
Sergio Lo Russo
2
, Amedeo Maddalena
1
and Giovanni Principi
1
1
Dipartimento di Ingegneria Meccanica, Universit` a di Padova, Settore Materiali,
via Marzolo 9, I-35131 Padova, Italy
2
Dipartimento di Fisica and CNISM, Universit` a di Padova, via Marzolo 8, I-35131 Padova,
Italy
E-mail: filippo.agresti@unipd.it
Received 7 November 2009, in final form 9 December 2009
Published 8 January 2010
Online at stacks.iop.org/Nano/21/065707
Abstract
The dehydrogenation kinetics of LiBH
4
dispersed on multi-walled carbon nanotubes
(MWCNTs) by the solvent infiltration technique has been studied. Commercial MWCNTs were
ball-milled for different milling times in order to increase the specific surface area (SSA) as
measured by the BET technique. Thermal programmed desorption measurements have been
performed using a Sievert’s apparatus on samples with different SSA of MWCNTs and different
LiBH
4
to MWCNT ratio. Pressure composition isotherms (PCI) have been obtained at different
temperatures in order to estimate the H and S of dehydrogenation. It has been observed
that the dispersion of LiBH
4
on MWCNTs leads to a lower dehydrogenation temperature
compared to pure LiBH
4
. Moreover, the dehydrogenation temperature further decreases with
increasing MWCNT surface area. An interpretation of the kinetic effect is proposed.
(Some figures in this article are in colour only in the electronic version)
1. Introduction
LiBH
4
is known as one of the most used compounds in
organic chemistry as a reducing agent for aldehydes, ketones,
acid chlorides, lactones, epoxides and esters [1] and can
be industrially prepared by metathesis reaction starting from
NaBH
4
and Li halides or chlorides [2, 3]. Recently, LiBH
4
has
been directly synthesized from a mixture of elements exposed
to hydrogen at 700
◦
C and 150 bar [4]. In a previous paper [5]
there has been demonstrated the possibility of the formation of
LiBH
4
at room temperature by high energy reactive milling of
the decomposition products of the reaction
LiBH
4
→ LiH + B + 3/2H
2
. (1)
LiBH
4
is also known as one of the best energy density
carriers. In fact, it is one of the most interesting and
studied complex hydrides for hydrogen storage, due to its
high theoretical gravimetric hydrogen capacity (18.4 wt%).
However, LiBH
4
releases only 13.4 wt% H
2
when decomposed
according to reaction (1), starting above 300
◦
C and having a
maximum desorption rate between 400 and 500
◦
C. Not all
the theoretical hydrogen content can be easily released, due to
the high stability of LiH which desorbs hydrogen only above
730
◦
C[6]. Besides the high dehydrogenation temperature, the
problem of using LiBH
4
as a hydrogen storage material is the
complexity of the recycling mechanism: as reported by Orimo
et al [7], reaction (1) is reversible only in extreme pressure and
temperature conditions (350 bar H
2
and 600
◦
C).
In order to improve thermodynamics and kinetics of
dehydrogenation of light metal hydrides, Vajo et al [8] have
proposed confining them in nanoporous scaffolds, exploiting
the favourable properties of nanostructured materials and
avoiding sintering and agglomeration during cycling. In recent
papers it has been shown that LiBH
4
milled with carbon
nanotubes [9] and included in mesoporous carbon [10] displays
a decrease of dehydrogenation temperature. Beneficial effects
of carbon addition on the dehydrogenation kinetics have
also been observed for the Li–B–Mg–H system [11]. In
the present paper it is shown that LiBH
4
deposited on
MWCNTs previously modified by ball milling exhibits a
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