Electronic Supplementary Material (ESI) for Energy & Environmental Science
This journal is © The Royal Society of Chemistry 2013
Improved Hydrogen Storage Performance of Ca(BH4)2: A Synergetic
Effect of Porous Morphology and in Situ Formed TiO2
Jian Gu,a Mingxia Gao,* a Hongge Pan,a Yongfeng Liu,a Bo Li,a Yanjing Yang,a Chu
Liang,a Hongliang Fu,a and Zhengxiao Guob
Supplementary information
Synthesis of Ca(BH4)2:
Anhydrous CaCl2 and NaBH4 in a molar ratio of 1 : 2 was firstly ball milled in a
homemade stainless steel jar filled with THF for 24 h on a planetary ball mill
(QM-3SP4, Nanjing) with a rotating speed of 300 rpm. The ball-to-powder weight
ratio was 10 : 1. And then, the ball-milled suspension was filtered in a homemade
filtration system to remove the precipitates of NaCl and unreacted chemicals.
Subsequently, the clarified filtrate was introduced to a homemade distillation system,
in which the solvent was removed from the filtrate at 55 °C with a dynamic vacuum
until the product became a white solid, viz., the as-prepared Ca(BH4)22THF. This
white solid was then ground with a mortar and pestle to powder, which was then
transformed to a homemade desolvated apparatus. A treatment under dynamic vacuum
at 170 °C for 16 h was further performed to remove the THF adduct from
Ca(BH4)22THF much completely.
The calculation of the ratios of the evolved gases from the Ca(BH4)2+0.1Ti(OEt)4
mixture during heat treatment:
The details of the calculation of the ratios of the evolved gases from the
Ca(BH4)2+0.1Ti(OEt)4 mixture upon heating to 160 °C for 1 h based on the data
shown in Fig. 3 as the following:
The weight loss in the process can be obtained from the TG measurement (Fig.
3(b)), which is denoted as WTG here. In this case, the evolved gases in the heating
process is taken to be ideal gas mixture, and the total number of moles of the evolved
1
Electronic Supplementary Material (ESI) for Energy & Environmental Science
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gases of C2H6, C2H6O and H2 can be obtained from the pressure change of the
container with a fixed volume by the state function of PV=(n1+n2+n3)RT, where n1, n2
and n3 are denoted as the number of moles of C2H6, C2H6O and H2, respectively,
evolved from one mole of Ca(BH4)2+0.1Ti(OEt)4. The total number of moles of the
evolved gases after the heat treatment is obtained from Fig. 3(c), which is of 0.69
moles.
The correlations of the weights of the different gases evolved after the heat
treatment and the original solid mixture of Ca(BH4)2+0.1Ti(OEt)4, and the number of
moles of the different gases are expressed as the following:
M1  n1  M 2  n2  M 3  n3 T GW(  mMi x1 )
n1  n2  n3 0 . 6 9
(1)
where M1, M2, M3, Mmix are denoted as the molecular weights of C2H6, C2H6O, H2 and
Ca(BH4)2+0.1Ti(OEt)4 mixture, respectively. Combining the equivalent numbers of
carbon atoms in the evolved gases and in the 0.1 mole of Ti(OEt)4 in the mixture,
2  n1  2  n2  0.1  8
(2)
the number of moles of C2H6, C2H6O and H2 (n1, n2 and n3, respectively) evolved
from one mole of Ca(BH4)2+0.1Ti(OEt)4 mixture are calculated as 0.2, 0.2 and 0.3, as
shown in eqn (4) of the main article.
2
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(a) 
(b)
o
as-prepared Ca(BH4)2 des to 320 C
o
as-prepared Ca(BH4)2 des to 320 C


Intensity (a.u.)




 
as-prepared Ca(BH4)2
   
Transmittance (a.u.)



 as-prepared Ca(BH4)2


   
       
  

B-H
Ca(BH4)22THF
B-H
C-H
C-H
Ca(BH4)22THF
10
20
30
40
o
50
60
C-O
70
3000 2700 2400
2 Theta ( )
1200 1000
-1
800
Wavenumber (cm )
Fig. S1 XRD patterns (a) and FTIR spectra (b) of the as-prepared Ca(BH4)22THF, the
as-prepared Ca(BH4)2 and the Ca(BH4)2 desorbed to 320 °C.
0
1.1
H/M (wt%)
-2
-4
9.1
-6
as-prepared Ca(BH4)2
-8
-10
50
100
150
200
250
300
350
400
450
500
550
o
Temperature ( C)
Fig. S2 Hydrogen desorption curve of the as-prepared Ca(BH4)2. The heating rate is
2 °C min-1.
3
Electronic Supplementary Material (ESI) for Energy & Environmental Science
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(a)
(b)
150 nm
400 nm
Fig. S3 SEM images of the commercial TiO2 (a) and home-made TiO2 derived from
Ti(OEt)4 (b).
(101)

-Ca(BH4)2
 TiO2






Intensity (a.u.)





 
(d)
  







(c)


(b)




10
20
30
40
50
o
60
70


80
(a)
90
2 Theta ( )
Fig. S4 XRD patterns of the commercial TiO2 (a), home-made TiO2 (b), the mixtures
of Ca(BH4)2+0.1TiO2 (commercial) (c) and Ca(BH4)2+0.1TiO2 (home-made) (d).
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Electronic Supplementary Material (ESI) for Energy & Environmental Science
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(a)
(b)
500 nm
4mm
4mm
(d)
(c)
500 nm
2mm
2mm
Fig.
S5
SEM
images
of
the
Ca(BH4)2+0.1TiO2
(commercial)
(a)
and
Ca(BH4)2+0.1TiO2 (home-made) (b) heated at 160 °C for 1 h; the Ca(BH4)2+0.1TiO2
(commercial) (c) and Ca(BH4)2+0.1TiO2 (home-made) (d) desorbed to 420 °C for 1 h
(d).
(a)
(b)
1mm
(d)
(c)
1mm
Fig. S6 SEM images (a, c) and the corresponding EDS mapping of Ti (b, d) for the
porous CaB2H7/0.1TiO2 (a, b) and Ca(BH4)2+0.1TiO2 (home-made) (c, d).
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Electronic Supplementary Material (ESI) for Energy & Environmental Science
This journal is © The Royal Society of Chemistry 2013
(a)
(b)
400 nm
(c)
4mm
(d)
4mm
4mm
Fig. S7 SEM images of the Ca(BH4)2+0.1Ti(OEt)4 mixture desorbed to 280 °C (a),
the
as-milled
Ca(BH4)2
(b),
Ca(BH4)2+0.1TiO2(commercial)
(c)
and
Ca(BH4)2+0.1TiO2 (home-made) (d).
-10.5
4
1
2
ln ( / Tm )
-11.0
-11.5
Equation
Weight
-12.0
Ea1=155 kJ mol
-1
Residual Sum
of Squares
Ea2=151 kJ mol
-1
Pearson's r
Ea3=145 kJ mol
-1
Ea4=118 kJ mol
-1
Adj. R-Square
Ca
Ca
+Ti
+Ti
+Ti(in)
-12.5
+Ti(in)
+porous
-13.0
0.00155
0.00160
0.00165
+porous
3
2
0.00170
0.00175
0.00180
0.00185
-1
1 / Tm (K )
Fig. S8 Kissinger’s plots of of the as-milled Ca(BH4)2 (1), Ca(BH4)2 with TiO2
(commercial (2) and home-made (3)) externally added, and the porous
CaB2H7/0.1TiO2 system (4).
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10
CaB2H7/0.1TiO2
-1
H1=52.2 kJ mol H2
5
-1
H2=49.3 kJ mol H2
-1
-1
Ca(BH4)2+0.1TiO2(home-made)
-1
DSC (mW mg )
H3=48.5 kJ mol H2
0
-5
H4=36.9 kJ mol H2
Ca(BH4)2+0.1TiO2(commercial)
BM Ca(BH4)2
-10
endo
-15
50
100
150
200
250
300
350
400
450
500
550
o
Temperature ( C)
Fig. S9 DSC curves of the as-milled Ca(BH4)2, Ca(BH4)2 with TiO2 (commercial or
home-made) externally added, and the porous CaB2H7/0.1TiO2 system.
Time (min)
50
100
150
200
0
300
-1
250
200
-2
150
-3
o
Temperature ( C)
H/M (wt%)
0
100
1st desorption
2nd desorption
3rd desorption
4th desorption
5th desorption
-4
-5
50
0
0
50
100
150
200
Time (min)
Fig. S10 Desorption curves of the first 5 desorption/absorption cycles of the porous
CaB2H7/0.1TiO2 system dehydrogenated at 300 °C for 1 h and hydrogenated at
350 °C and 90 bar H2 pressure for 1 h.
7