An Approach on the Hydrogen Absorption in Carbon Black after Gamma Irradiation

doi:10.4236/ampc.2013.37040

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Advances in Materials Physics and Chemistry, 2013, 3, 295-298

Published Online November 2013 (http://www.scirp.org/journal/ampc)

http://dx.doi.org/10.4236/ampc.2013.37040

Open Access AMPC

An Approach on the Hydrogen Absorption in Carbon

Black after Gamma Irradiation

Antonio Madroñero1, Mario Culebras2, Andrés Cantarero2, Clara M. Gómez2, César Mota1,

José M. Amo1, José I. Robla1

1Centro Nacional de Investigaciones Metalúrgicas (CSIC), Madrid, Spain

2Instituto de Ciencia de los Materiales, Universidad de Valencia, Valencia, Spain

Email: [email protected], mario.culebras@uv.es, [email protected], [email protected],

[email protected], [email protected], [email protected]

Received August 25, 2013; revised September 28, 2013; accepted October 14, 2013

cense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

In this work, different samples of an industrial carbon black are used to study the hydrogen intake from an over pres-

surized atmosphere and its changes due to alteration of its level of crystallinity produced by γ-irradiation. The monitor-

ing of the hydrogen adsorption was made by means of thermogravimetric analysis and by measurements of some elec-

trical parameters as the Seebeck coefficient. X-ray diffraction shows that the irradiation diminishes the level of crystal-

line perfection. These results show interesting possibilities to use carbon black as cheap hydrogen absorbers.

Keywords: Carbon Black; Hydrogen Storage; Carbon Semiconductor; Seebeck’s Effect; Gamma Irradiation

1. Introduction

As it is well known, hydrogen plays a double role in

carbons when the carbons store hydrogen showing elec-

trical parameters figures that correspond to semiconduc-

tor materials [1]. As a result, to increase the hydrogen

storage capability of carbons is a good path to obtain

cheap semiconducting carbons. As the hydrogen intake

starts in the surface of the solids, many works were ori-

ented to the improvement of the surface paying attention

to the optimization of the hydrogen adsorption. Follow-

ing this direction, as it is commonly accepted, the amount

of defects and the distribution and sizes of them were the

main parameters to achieve a good hydrogen adsorption.

The linear relationship between the hydrogen uptake and

the specific surface area (SSA) is independent of the na-

ture of the carbon material [2]. In the development of

carbonaceous absorbers for hydrogen storage there are

many studies showing different techniques to activate the

carbon’s surface, with chemicals [3] and with gas etching

[4]. Most of the commercial active carbons available

nowadays to store hydrogen correspond to this stage.

After that, the possibility was explored to use physical

treatments to produce the required defects. Radiation by

γ-rays is a powerful tool to produce defects in the surface

and inner defects in carbons [5].

In carbon nanotubes, γ-irradiation had been more ef-

fective than chemical etching to activate carbon surfaces

[6]. In the present work, we will study the capability of

γ-rays to increase the semiconducting character of carbon

black samples to increase the hydrogen absorption.

2. Materials

The material used in the present work was from Black

Pearls 1400, manufactured by Cabot™. According to the

manufacturer’s information, the specific surface of this

material is 560 m2/g. We have selected carbon black

specimens with the best performance. The surface energy

of commercial carbons blacks is from 70 - 200 m2/g [7]

and the figure of the surface area is a liable identifier of

carbons with a good capacity for hydrogen adsorption [8].

The samples were subjected to two successive treatments:

hydrogenation and irradiation. The hydrogenation was

performed in a pressurize hydrogen atmosphere at 20 bar

and room temperature for 180 minutes. In these condi-

tions, a hydrogen adsorption on the carbon black powder

took place. The used hydrogen was Ultrapure Plus ×50S

(99.9992%), supplied by Carburos Metalicos™. In the

irradiation process, the sample was exposed to a 504-kGy

irradiation with 60Co isotopes. The sample exposure to

the radioisotopes was carried out by immersion in a wa-

A. MADROÑERO ET AL.

296

ter well where the radioisotopes were located. The loca-

tion was the Nayade facility, existing at the Centre of

Energy, Environment and Technology Research (Centro

de Investigaciones Energéticas, Medioambientales y

Tecnólogicas, CIEMAT), in Madrid, Spain.

For this study, four samples are prepared in order to

study hydrogenation and irradiation effects in the sam-

ples as summarized in Table 1.

3. Methods

3.1. Thermogravimetrical Analysis

The four samples analysed here were examined by Ther-

mal Gravimetry (TGA), using the equipment DTA/TGA

SETARAM Setsys Evolution. The weight of the four

samples was around 13 mg.

The measurement supposed a heating from room tem-

perature to 1073 K in an argon atmosphere (20 ml/min).

The heating rate for the four samples was:

1) From room temperature up to 673 K: the heating

rate was 5 K/min.

2) From 673 K up to 873 K: the heating rate was 3

K/min.

3) From 873 K to 1073 K: the rate was 5 K/min.

The TGA curves were recorded using the software

CALISTO v1.0.95.

3.2. X-Ray Diffracti on

Another technique of examination was X-Ray Diffrac-

tion (XRD), performed in a Siemens D5000 diffractome-

ter with Ni-filtered Cu Kα radiation. The X-ray tube was

operated at 40 kV and 30 mA. The experimental diffrac-

tometers were collected with a step of 0.03˚ (2θ) and an

averaging time of 0.6˚/min. The XRD patterns of the

samples were identified with the Joint Committee on

Powder Diffraction Standards (JCPDS) files.

3.3. Electrical Parameters Measurements

The samples were compacted in thin pellets and four

contacts with silver paste were deposited on the surface

for electric characterization. In order to measure the elec-

trical conductivity, the Van der Pauw method was used

[9]. The electrical conductivity can be obtained solving

Table 1. Treatments in the carbon black samples.

Sample Treatment

TN-sH without treatment

TN-H Hydrogenation

CN-sH Irradiation

CN-H Irradiation and hydrogenation

the Van der Pauw equation:

dR dR



  1



 (1)

To calculate R1 and R2 four contacts, labelled A, B, C

and D, were used. R1 is obtained as 1

DAC

RV I and

2AB CD

RVI



, were V and I are the voltage and intensity

across the sample, respectively. A Keithley 2400 mul-

timeter was used as a current source.

The Seebeck coefficient is determined as the ratio be-

tween the electrical potential, , and the temperature

difference,

V



, that is:





 (2)

For the temperature control, a “Lakeshore 340 Tem-

perature Controller” was used and for recording the po-

tential data a “Keithley 2750 Data Acquisition Switching

System”.

4. Results and Discussion

Figure 1 shows the results of the TGA. The more rele-

vant feature in sample CN-H is that there is an increase

in weight, more pronounced at temperatures about 500 -

700 K. It is easy to explain it as a process of argon ab-

sorption [10,11] that takes place in the surface of the car-

bonaceous materials. In samples TN-H, CN-sH and TN-

sH, Ar adsorption at the sample surface was not ob-

served.

On the other hand, in Tabl e 2, the weight loss, a pa-

rameter that supplies information about the hydrogen

storage I shown. It is simple to see that the irradiated

samples stores more hydrogen that the non-irradiated

ones. A figure of hydrogen content larger than 10% w/w

has interest looking at the possibility of use carbon

blacks as cheap hydrogen adsorbers in other fields of the

hydrogen economy as in the construction of portable can-

ister with stored hydrogen for the automotive industry.

In Figure 2, referred to non-hydrogenated samples, it

300 400 500 600 700 800 90010001100

-20

-15

-10

-5

300 400 500 600 700 800 90010001100

-20

-15

-10

-5

TG (%)

Temperature (K)

CN-H

CN-sH

TN-H

TN-sH

Figure 1. Thermal gravimetric analysis of the samples.

Open Access AMPC

A. MADROÑERO ET AL. 297

020 40 60 80100120

100

200

300

400

500

600

700

800

900

TN-sH

CN-sH

Counts

2 Theta (degrees)

Figure 2. XRD plot of non-hydrogenated sample s.

Table 2. Weight loss (in %) during the TGA showing the

variations in the different temperature ranges.

Δm1 (%) Δm2 (%) Δm3 (%)

Sample

(273 - 673 K) (673 - 873 K) (873 - 1073 K)

ΣΔm (%)

CN-H 1.596 −9.877 −10.444 −18.69

CN-sH −1.184 −2.826 −2.329 −13.0

TN-H −7.167 −2.839 −2.219 −12.11

TN-sH −8.338 −2.723 −1.987 −13.0

is possible to see that the effect of the irradiation is to

diminish the crystalline perfection displayed as an im-

pairing of the slenderness of the diffraction peak; the

irradiated carbon black becomes more similar to an

amorphous sample. The fact that γ irradiation increases

the hydrogen intake in carbon materials is in agreement

with the knowledge that amorphous carbons are better

absorbers than crystalline carbons [12].

Similar results are obtained in Figure 3 for the hydro-

genated samples. Actually, the diffraction is a powerful

tool to distinguish between irradiated and non-irradiated

materials, but not very reliable to evaluate the level of

over hydrogenation.

In the same way, if we proceed to evaluate the crystal-

line size Lc using the Scherrer’s formula [13], as shown

in Table 3, the effect of the irradiation is to diminish Lc.

Similar evolution of XRD is known in carbon nano-

tubes irradiated with γ-rays [14].

The electrical properties of the samples have been ob-

tained using the Van der Paw’s technique described

above and the results are shown in Table 4, where it is

possible to see that the absorption of hydrogen decreases

the electrical conductivity, as, it is known for similar

materials [15].

The influence of the irradiation process is effective

regarding the change in Seebeck’s coefficient. In Table 4

we can observe that the irradiation per se improves the

0 20406080100

100

200

300

400

500

600

700

800 TN-H

CN-H

Counts

2 Theta (degrees)

Figure 3. XRD plot of hydrogenated samples.

Table 3. Determinati on of cryst alline size usi ng the Scherrer’s

formula.

Sample L [Å]

CN-H 6.8

CN-sH 7.3

TN-H 7.1

TN-sH 7.3

Table 4. Results of the measurements of electric conductiv-

ity and Seebeck’s effect of the carbon black samples.

Sample σ (S/cm) S (μV/K)

TN-sH 2.00 0.87 ± 0.01

TN-H 1.49 4.2 ± 0.2

CN-sH 1.41 2.63 ± 0.05

CN-H 1.09 3.25 ± 0.05

Seebeck’s coefficient, but it is also remarkable that the

intake of hydrogen increases that coefficient.

5. Conclusion

According to the above results, it is possible to conclude

that the use of previous γ-irradiation improves the hy-

drogen intake at room temperature in carbon black from

an over-pressurized atmosphere. The carbon black is

converted into a more amorphous material by the effect

of the irradiation. The X-ray diffraction is a valid tech-

nique to observe the changes that take place in the carbon

black as a consequence of γ-irradiation and the alteration

in the crystalline structure is explained by the change in

the lattice parameter Lc.

6. Acknowledgements

We would like to acknowledge support from the Spanish

Open Access AMPC

A. MADROÑERO ET AL.

Open Access AMPC

298

Ministry of Finances and Competitivity (MINECO),

through the grant of the Consolider-Ingenio 2010 project

Nanotherm (CSD2010-00044).

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