Cobalt borate catalysts for hydrogen production via hydrolysis of sodium borohydride

Article abstract of DOI:10.1016/j.jallcom.2011.10.033

Cobalt borides are known to be active catalysts in NaBH₄ hydrolysis. In situ generation of the active cobalt boride phase in sodium borohydride aqueous solutions is accompanied by formation of cobalt borate whose contribution to the overall cat

Full text of DOI:10.1016/j.jallcom.2011.10.033

Journal of Alloys and Compounds 513 (2012) 266–272
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Journal of Alloys and Compounds
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Cobalt borate catalysts for hydrogen production via hydrolysis of sodium
borohydride
A.M. Ozerova, V.I. Simagina, O.V. Komova∗, O.V. Netskina, G.V. Odegova, O.A. Bulavchenko, N.A. Rudina
Boreskov Institute of Catalysis, Pr. Akademika Lavrentieva 5, Novosibirsk 630090, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 July 2011
Received in revised form 11 October 2011
Accepted 12 October 2011
Available online 20 October 2011
Cobalt borides are known to be active catalysts in NaBH4 hydrolysis. In situ generation of the active
cobalt boride phase in sodium borohydride aqueous solutions is accompanied by formation of cobalt
borate whose contribution to the overall catalytic activity of the system has not been studied in detail. In
this work an amorphous phase of cobalt borate, which transforms to Co2B2O5 upon crystallization, has
been synthesized and analyzed. As-synthesized cobalt borate shows high activity in NaBH4 hydrolysis
due to its reduction resulting in catalytically active cobalt-containing phase.
Keywords:
© 2011 Elsevier B.V. All rights reserved.
Cobalt borate
Cobalt boride
Sodium borohydride
Hydrolysis
1. Introduction
their high cost makes them prohibitive for wider applications.
Cobalt-based catalysts have recently emerged to potentially replace
Hydrogen storage and conversion are essential for the emerging
hydrogen economy. One of the important research areas of today
is to identify the most effective hydrogen storage materials. Sev-
eral complex hydrides, including NaBH4, LiBH4, NaAlH4, Mg(BH4)2,
and NH3BH3, have been found to be potentially suitable for hydro-
gen storage because of their high hydrogen storage capacity [1,2].
Sodium borohydride, NaBH4, in particular, is the focus of interest
since the late 1990s because of its stability in alkaline solutions,
non-flammability, non-toxicity, environmental safety and the high
theoretical hydrogen content [3–5]. It is also the least expensive
metal hydride readily available commercially, and it is currently
one of the best candidates for use in portable devices [6].
noble metals in NaBH4 hydrolysis [13], including Co nanoparti-
cles [14–16], metallic cobalt [7,17], cobalt salts [7,8,17,18], cobalt
oxides [16,18–20], Co–B hollow spheres [21], and supported Co-
containing catalysts [22–26]. However, most of the work in this
area has been devoted to cobalt boride, CoxB, either in its pure
form [27–31] or with dopants (Ni, Fe, Cu, W, Cr, Mo, Mn, and P)
[25,32–35].
There are two synthetic approaches to prepare a catalytically
active cobalt boride phase, ex situ and in situ. In the ex situ prepa-
ration common cobalt salts are reduced with a NaBH4 solution
followed by separation, washing, and drying of the black CoxB pre-
cipitate [27–31]. In the in situ route the active boride phase is
obtained from cobalt compounds directly in the medium of NaBH4
hydrolysis reaction [7,8,17,18]. The latter approach simplifies con-
siderably the catalyst preparation procedure. In both cases the
reduction process can be described as follows:
At ambient temperature the complete hydrolysis of sodium
borohydride takes place only in the presence of a suitable catalyst:
cat
NaBH4 + 2H2O−→ NaBO2 + 4H2
(1)
CoCl2 + 4NaBH4 + 9H2O → Co2B + 4NaCl + 12.5H2 + 3B(OH)3
The composition of the sodium borate may vary depending on
the process conditions. Several sodium borate species have been
identified, including NaBO2·xH2O (x = 2, 4) and Na2B4O7·xH2O (x = 5,
10) [7–9].
There have been many efforts to improve catalytic systems for
NaBH4 hydrolysis. Catalysts containing noble metals (Pt, Rh, Ru)
have shown the best performance in this process [10–12], but
(2)
The final composition of products forming in the reaction of
sodium borohydride with cobalt salts in aqueous solutions greatly
depend on the reaction conditions, such as reagent concentrations,
the order of their mixing, pH of the solution, washing and dry-
ing procedures, and the storage conditions [36,37]. Along with the
amorphous CoxB phases (x = 1 ÷ 3) some other phases may form
as well, such as metallic cobalt and amorphous cobalt borate. The
latter is most likely the result of interaction of cobalt ions with
∗
Corresponding author. Tel.: +7 3832 3307458; fax: +7 3832 3307336.
E-mail address: komova@catalysis.ru (O.V. Komova).
0925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2011.10.033

A.M. Ozerova et al. / Journal of Alloys and Compounds 513 (2012) 266–272
267
by-products of sodium borohydride hydrolysis which, according to
Glavee et al. [36], can be expressed as
Co2+ + 2NaBO2 → 2Na+ + Co(BO2)2
(3)
Transmission electron microscopy (TEM) studies of CoxB particles
formed in situ in the presence of NaBH4 indicated that they had
almost always been covered in a layer of oxygen-containing cobalt
and boron compounds [8,13,14,37]. After calcination of these par-
ticles, a Co2B2O5 phase had been found among the crystallization
products [8] suggesting that the amorphous phase of cobalt borate
was present in the sample before calcination. While the catalytic
behavior of CoxB is well known, questions remain on how the pres-
ence of amorphous cobalt borate will affect the NaBH4 hydrolysis,
since the catalytic activity of cobalt borate in this reaction has not
been studied. If this effect is unfavorable, a procedure should be
developed to minimize the amount of amorphous cobalt borate in
Co–B catalysts.
Fig. 1. SEM image of the Co–B–O sample.
The purpose of this work has been to synthesize an individual
phase of amorphous cobalt borate, Co–B–O, similar to that found
in Co–B catalysts, and to compare its catalytic activity in sodium
borohydride hydrolysis with other cobalt compounds.
Jena) equipped with a standard diffuse reflectance attachment in the region of
200–900 nm.
FTIR spectra were recorded in air at room temperature on a Bomen MB-102
Fourier spectrometer. For FTIR analysis samples were compressed into thin wafers
with cesium iodide, CsI.
2. Experimental
Thermal analysis was performed on a STA 449C Jupiter instrument in a flow
of helium (10 ml/min) at temperatures from 25 to 1000 ◦C and the heating rate of
10 ◦C/min.
2.1. Chemicals
The high-temperature diffraction studies were performed using a D8 diffrac-
tometer (Bruker, Germany) using a high-temperature X-ray chamber (Anton Paar,
Austria). The instrument was equipped with a Gebel mirror (Bruker, Germany)
which formed a parallel X-ray beam. Cu K␣ radiation with a wave length of
All commercial chemical reagents were used as received, including sodium
borohydride, NaBH4 (Acros Organics, 98 wt.%), cobalt (II) chloride hexahydrate,
CoCl2·6H2O (GOST 4525-77), cobalt (II) nitrate hexahydrate, Co(NO3)2·6H2O (GOST
4528-78), cobalt (II, III) oxide, Co3O4 (GOST 4467-79), cobalt (II) oxide, CoO (GOST
18671-73), cobalt (II) carbonate hydrate, 2CoCO3·3Co(OH)2·H2O (GOST 5407-78),
sodium hydroxide, NaOH (GOST 4328-77), hydrogen peroxide, H2O2 (GOST 10929-
76), urea, CO(NH2)2 (GOST 2081-92), and acetone, CH3COCH3 (GOST 2603-79).
˚
ꢀ = 1.5418 A was used. The measurements were carried out at a residual pressure of
5 × 10−6 bar in the range of angles from 15◦ to 70◦ in steps of 0.05◦. The collection
time was from 5 to 20 s.
2.4. Hydrogen generation experiments
2.2. Sample preparation
Hydrogen generation experiments were carried out at 40 ◦C in a temperature-
controlled glass internal mixing reactor equipped with a magnetic stirrer at 800 rpm.
A freshly prepared aqueous solution of NaBH4 (1.2 mmol, 10 ml) was placed into the
reactor. The known amount of catalyst (0.0117 g) was then added and the volume
of produced hydrogen gas was measured with a 100 ml gas burette with a resolu-
tion of 0.2 ml. The data obtained were corrected to N.T.P. Based on three repeated
experiments under the same conditions the experimental uncertainty was less than
5%.
The following catalysts were studied, Co–B–O, CoCl2·6H2O, Co3O4, CoO, CoOOH,
CoCO3·Co(OH)2·0.22H2O, 2CoCO3·3Co(OH)2·H2O. When necessary, after the cat-
alytic reaction was complete the catalysts were separated from the reaction medium
by a magnet, rapidly washed with acetone, and dried at 80 ◦C for 3 h under vacuum,
and then studied by a set of physical methods.
The Co–B–O sample was synthesized using a modified version of the method
developed by Glavee et al. [36]. The procedure is based on the interaction of
cobalt chloride with sodium borate in an aqueous solution as follows. A solution of
CoCl2·6H2O (0.305 M, 200 ml) was added drop-wise to a solution of sodium borate
(0.61 M, 200 ml) at room temperature under stirring which resulted in instanta-
neous formation of a pink suspension. The solid Co–B–O product was filtered off,
thoroughly washed with distilled water, and dried in air at room temperature. We
observed that during washing the color of precipitate changed from pink to purple.
The solution of sodium borate used in the synthesis of Co–B–O was prepared
as follows. A solution of NaBH4 (0.12 M, 1200 ml) was subjected to hydrolysis with
CoCl2·6H2O (1.404 g) at 40 ◦C under mechanical stirring. After the hydrolysis reac-
tion was complete the sodium borate solution was separated from the catalyst and
evaporated to the required concentration. A portion of the solution was evaporated
until crystals of sodium borate precipitated which were then separated from the
mother liquor, dried in a vacuum box at 80 ◦C for 3 h and studied by FTIR spec-
troscopy.
The CoOOH sample was prepared by the precipitation-oxidation method in an
aqueous solution as described in [38]. The precipitation process was carried out at
50 ◦C via a drop-wise addition of a solution of Co(NO3)2·6H2O (0.6 M, 50 ml) to a
solution of NaOH (3.2 M, 100 ml) under constant stirring. 100 ml of H2O2 (50 wt.%)
was then added drop-wise to the reaction mixture under stirring. The solid product
was filtered off, thoroughly washed with distilled water and dried at 65 ◦C in air for
26 h. The resulting product was analyzed with XRD which confirmed it as the pure
CoOOH phase (JCPDS PDF card no. 26-1107).
The long-term cyclic stability of catalysts was tested by repeating the above
procedure of NaBH4 hydrolysis. After the first portion of NaBH4 (1.2 mmol, 10 ml)
was fully converted, a fresh portion of solid NaBH4 (1.2 mmol) was added to the
reactor.
3. Results and discussion
3.1. Characterization of the Co–B–O sample
To prepare the Co–B–O sample the synthesis conditions were
chosen as close as possible to the experimental conditions of the
catalytic hydrolysis of NaBH4 over cobalt chloride. To this effect the
sodium borate solution used in the Co–B–O synthesis was made not
by dissolving a commercial sodium borate reagent, but instead the
solution was used which was left after NaBH4 hydrolysis by CoCl2
(see Section 2). When thus prepared sodium borate solution was
allowed to react with CoCl2 a pink-to-purple Co–B–O precipitate
was formed; the purple color is indicative of several types of cobalt
borates as described in the literature [40–42].
The sample of CoCO3·Co(OH)2·0.22H2O (JCPDS PDF card no. 48-0083) was
prepared by homogeneous precipitation [39]. 500 ml of
a solution containing
Co(NO3)2·6H2O (0.1 M) and CO(NH2)2 (1 M) was heated to 85 ◦C and kept at this
temperature for 3 h under constant stirring. The solid product obtained was filtered
off, thoroughly washed with distilled water and dried at 110–130 ◦C in air for 7 h.
2.3. Sample characterization
The morphology of the Co–B–O sample was studied by scanning electron
microscopy (SEM) using a JSM 6460LV microscope (JEOL, Japan).
Bulk concentrations of Co and B in the studied samples were determined by
inductively coupled plasma atomic emission spectrometry using an Optima 4300
DV instrument.
The dried Co–B–O sample was X-ray amorphous. As shown in
Fig. 1, SEM images revealed that the Co–B–O sample was com-
posed of dense irregular particles tens to hundreds micrometers
The diffuse reflectance electronic spectra of the Co–B–O sample were mea-
sured in air at room temperature on a Specord M40 spectrophotometer (Carl Zeiss,

268
A.M. Ozerova et al. / Journal of Alloys and Compounds 513 (2012) 266–272
Fig. 3. FTIR spectra of sodium borate remaining after hydrolysis of NaBH4 and of
the Co–B–O sample.
Fig. 2. Diffuse reflectance electronic spectrum of the Co–B–O sample.
in size, with bigger particles consisting of smaller scale-shaped
particles. The chemical analysis indicated that the sample con-
tained 37.00 wt.% Co and 7.41 wt.% B which corresponds to the
molar ratio Co:B = 1:1.09. The sodium content in the sample was
less than 0.01 wt.%. Based on this chemical composition and the
TG-DTA data (see below), the chemical formula of the Co–B–O
sample can be expressed as 2CoO·B2O3·4H2O, using a nomencla-
ture traditionally used for metal borates. The amorphous cobalt
borate phase obtained by Glavee et al. under similar experimental
conditions [36] was identified as Co(BO2)2 (molar ratio Co:B = 1:2).
The lower molar ratio obtained in our case was most likely due to
polymerization and association of borate ions in aqueous solution
[40].
Fig. 2 shows a diffuse reflectance electronic spectrum of the
as-synthesized Co–B–O sample in the region of d-d transitions of
cobalt ions. In this spectral region there is a broad absorption band
with a maximum at 560 nm. Similar absorption was observed in
[41] for the amorphous Co2B2O5 phase where it was attributed to
d–d transitions of Co2+ ions in the distorted octahedral coordina-
tion.
FTIR spectra of the as-synthesized Co–B–O sample and of the
sodium borate prepared via evaporating the solution after NaBH4
hydrolysis (see Section 2) are presented in Fig. 3. A direct com-
parison of the observed sodium borate spectrum with those of
other borates [43,44] by its position, shape and the half-width of
absorption bands, indicates that this spectrum most closely resem-
bles Na2B4O7·xH2O. The band at 3475 cm−1 corresponds to the
valence vibrations of O–H groups. The band at 1635 cm−1 is char-
acteristic of the deformational vibrations of H–O–H indicating the
presence of water. The bands at 1359 cm−1 and 883 cm−1 are due
to asymmetric and symmetric vibrations in the B(3)–O group. And
the bands at 1027 cm−1 and 736 cm−1 are due to asymmetric and
symmetric vibrations in the B(4)–O group. The presence of three-
and four-coordinated boron species is consistent with the struc-
ture of hydrated sodium tetraborate, where polyborate anions,
[B4O5(OH)4]2−, are known to contain two trigonal BO3 groups and
two tetragonal BO4 groups [43]. Moreover, Na2B4O7·xH2O (x = 5, 10)
Fig. 4. FTIR spectra of the cobalt boride catalysts formed in situ via hydrolysis of
NaBH4 using CoCl2 and Co3O4.
was reported among products of NaBH4 hydrolysis [7,9]. In the FTIR
spectrum of Co–B–O the observed coordination of borate anions
appears to be identical to that of [B4O5(OH)4]2−
.
IR absorption bands due to B–O bond vibrations have been also
observed in the IR spectra of catalysts formed in situ during NaBH4
hydrolysis with CoCl2 and Co3O4 (Fig. 4). Similar IR absorption
bands were reported previously for other cobalt boride systems,

A.M. Ozerova et al. / Journal of Alloys and Compounds 513 (2012) 266–272
269
Fig. 6. XRD patterns acquired after vacuum treatment of the Co–B–O sample at 25,
Fig. 5. TG-DTA curves for the Co–B–O sample.
500, 600 and 700 ◦C.
where they were tentatively attributed to surface-adsorbed borate
anions [13,29,45]. However this earlier attribution may not be
entirely correct. Judging by high intensity of absorption bands in
the borate anion absorption region this IR pattern is most likely
an indication of the amorphous cobalt borate phase expected to
form in these samples [8,36]. Possible presence of such amorphous
phases should be taken into consideration in further studies of any
relationships between their catalytic activity and composition.
Thermal TG-DTA analysis of the Co–B–O sample provides an
additional insight into its nature and the underlying structure. Our
results are in agreement with the results previously reported for a
hydrated form of amorphous cobalt borate [40,46]. An endothermic
peak at 132 ◦C can be seen in the TG-DTA curves presented in Fig. 5.
This peak corresponds to desorption of significant amounts of struc-
tural water and is accompanied by a mass loss as high as 22.15 wt.%,
or 4 water molecules per 2CoO·B2O3, in agreement with the results
of the chemical analysis (see above). Further heating leads to two
exothermic maxima, a small one at 560 ◦C and a rather large maxi-
mum at 604 ◦C, while the mass loss remains almost negligible, only
1.3 wt.%. Such strong exothermic effects during crystallization are
believed to be due to borate regrouping, i.e. due to transformation
of amorphous borates into their crystalline forms [40,46]. Simi-
lar strong exothermic effects were reported earlier when studying
crystallization of the amorphous cobalt boride resulting from the
interaction of sodium borohydride with cobalt salts in aqueous
solutions [8], and the following phases of cobalt borate were found
among the crystallization products, Co(BO2)2 [47], Co3(BO3)2 [47]
and Co2B2O5 [8].
Co2B2O5 upon heating at elevated temperatures. The formation of
crystalline Co2B2O5 was also observed in [8] when studying crys-
tallization products of cobalt boride catalysts formed in situ from
cobalt chloride and sodium borohydride in solutions. Positive IR
identification of the amorphous cobalt borate phase suggests its
presence in other similar systems as well (Fig. 4), and justifies the
purpose of a more detailed study of the catalytic properties of the
Co–B–O phase in the reaction of sodium borohydride hydrolysis as
described below.
In this work powder X-ray diffraction has been used to iden-
tify crystalline phases forming in the Co–B–O sample under heating
under vacuum at temperatures before and after the borate regroup-
ing transformation. The XRD diffraction patterns recorded for the
as-synthesized Co–B–O sample and for this sample after heating
at 500, 600 and 700 ◦C are compared in Fig. 6. In the starting
material the XRD pattern shows a broad featureless peak in the
region of 30–40◦ confirming that the sample is amorphous. Pro-
longed heating of this sample at 500 ◦C, and even at 600 ◦C, did
not result in any substantial changes in the diffraction pattern.
Only at temperatures above the borate regrouping temperature
(700 ◦C) the formation of Co2B2O5 phase [42] was observed. No
other phases were found whose formation could be expected in the
course of reaction of sodium borate alkaline solution with cobalt
chloride.
We can conclude, that the Co–B–O compound synthesized
in this work constitutes a hydrated amorphous phase of cobalt
borate with a composition 2CoO·B2O3·4H2O, which crystallizes as
Fig. 7. Catalytic activity of the Co–B–O sample in the hydrolysis of NaBH4 at 40 ◦C in
(a) compared with CoCl2·6H2O, Co3O4 and CoO, and in (b) compared with CoOOH,
CoCO3·Co(OH)2·0.22H2O and 2CoCO3·3Co(OH)2·H2O.

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A.M. Ozerova et al. / Journal of Alloys and Compounds 513 (2012) 266–272
Fig. 8. Stability tests for the Co–B–O sample in hydrolysis of NaBH4 at 40 ◦C.
Fig. 9. FTIR spectra of the initial Co–B–O sample, and this sample after 1 and 16
cycles of NaBH4 hydrolysis.
3.2. The catalytic activity of the Co–B–O sample
This decline in activity has been explained by oxidation of the cata-
lysts’ active surfaces and by accumulation of the reaction products
[9,14,33].
The kinetic curves of hydrogen release during hydrolysis of
NaBH4 in the presence of the synthesized Co–B–O sample and some
of the other cobalt compounds are shown in Fig. 7. The catalytic
activity of Co–B–O is high and compares favorably with CoCl2·6H2O,
CoO and Co3O4 compounds which are known to produce the
catalytically active phase of cobalt boride in situ under the reac-
tion conditions [4,16,20]. The catalytic activity of Co–B–O exceeds
considerably the catalytic activities of other cobalt oxide com-
pounds studied, including CoOOH, CoCO3·Co(OH)2·0.22H2O, and
2CoCO3·3Co(OH)2·H2O (Fig. 7b). Also resembling CoO and Co3O4,
in Co–B–O we observe an activation period during the initial stage
of reaction with a very low rate of hydrogen generation. This acti-
vation period is determined by the time required for the insoluble
cobalt compounds to become reduced into the highly active amor-
phous phase of cobalt boride [13,18]. This reduction rate correlates
with their catalytic activity [20].
As noted above, the active catalytic systems shown in Fig. 7a,
including CoCl2·6H2O, Co3O4, and CoO, tend to rapidly become
reduced in the NaBH4 reaction medium to form the active amor-
phous phases of cobalt borides [4,16,20]. Similarly, the catalytic
activity of Co–B–O appears to be the result of its reduction by
NaBH4 to form the catalytically active boride phase. In the course
of NaBH4 hydrolysis the color of Co–B–O changes from purple to
black and the sample becomes ferromagnetic. Chemical analysis of
the black Co–B–O sample after the reaction showed 55.60 wt.% Co
and 6.76 wt.% B, i.e. the Co:B mole ratio increases from 1.09 to 1.5
after the reaction due to higher cobalt content. In the FTIR spec-
trum of the tested Co–B–O sample (Fig. 9) the absorption bands
corresponding to the starting Co–B–O sample were still present but
were significantly less pronounced. After the long-term stability
tests of Co–B–O (16 cycles) the absorption band intensities corre-
sponding to borate ions further decreased while the overall level
of the absorption increased. This suggests a reduction of Co–B–O
borate as it interacts with NaBH4 to form the cobalt-rich phase.
Formation of the new cobalt-containing phase is also confirmed
by X-ray diffraction analysis of this sample (Fig. 10). While at room
In the stability tests performed for the Co–B–O sample the
hydrogen generation rate gradually decreases with each hydrol-
ysis cycle (Fig. 8 Fig. 8). After 16 cycles of NaBH4 hydrolysis the
Co–B–O sample activity was reduced to about 50% of its initial
value. Such behavior is also characteristic of cobalt borides formed
in situ from CoCl2 and Co3O4 in the presence of NaBH4 [18,20,25,26].
Fig. 10. XRD patterns of the Co–B–O sample tested in NaBH4 hydrolysis and then treated at 25, 500 and 600 ◦C under vacuum.

A.M. Ozerova et al. / Journal of Alloys and Compounds 513 (2012) 266–272
271
activity of the catalytic system must be taken into consideration. In
this work the amorphous cobalt borate phase, 2CoO·B2O3·4H2O,
has been synthesized and characterized. The synthesized cobalt
borate has been shown to have high catalytic activity in NaBH4
hydrolysis comparable to that of CoCl2·6H2O, Co3O4, and CoO. High
activity of this cobalt borate has been shown to be due to its reduc-
tion in the presence of NaBH4 to form the active cobalt-containing
phase, presumably cobalt boride. The use of the alkaline solution
of NaBH4 and crystallization of cobalt borate to Co2B2O5 under
heating at 700 ◦C both have negative influence on the rate of its
reduction to the catalytically active phase, which in turn leads to
reduction in the hydrogen release rates.
Acknowledgements
The Russian Foundation for Basic Research (RFBR) is acknowl-
edged for financial support (grants no. 09-08-00505a and no.
09-08-00546a).
Fig. 11. Catalytic activity of the initial Co–B–O sample and of Co–B–O calcined at
500 ◦C and 700 ◦C in the hydrolysis of aqueous (0.12 M NaBH4) and alkaline (0.12 M
NaBH4, 0.04 M NaOH) solutions of NaBH4 at 40 ◦C.
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also remained amorphous upon heating in vacuum up to 500 ◦C.
At 500 ◦C, however, there appears a peak in the XRD pattern at
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40 s. In additional tests with the Co–B–O sample in the alkaline
solution of NaBH4 (0.12 M NaBH4, 0.04 M NaOH) the hydrogen
release rate is decreased considerably (Fig. 11), indicating the neg-
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phase. This observation may be explained by formation of basic
compounds of cobalt of low activity (Fig. 7b) upon the contact of
cobalt borate with the alkali solution of sodium borohydride.
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is negative as well. As can be seen in Fig. 11 a thermal treatment
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(Fig. 5) with preserving its amorphous state (Fig. 6) has no influence
on its catalytic activity. At the same time the increase of calcination
temperature to 700 ◦C, when the sample begins to crystallize to
form the Co2B2O5 phase (Fig. 6), there was observed considerable
reduction in the H2 generation rate.
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