Synthesis, characterization and hydrogen storage properties of microporous carbons templated by cation exchanged forms of zeolite Y with propylene and butylene as carbon precursors

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Synthesis, characterization, and hydrogen storage capacities of hierarchicalporous carbide derived carbon monolith†

Jiacheng Wang, Martin Oschatz, Tim Biemelt, Lars Borchardt, Irena Senkovska, Martin R. Loheand Stefan Kaskel*

Received 9th July 2012, Accepted 26th September 2012

DOI: 10.1039/c2jm34472f

Hierarchical porous carbide-derived carbon monoliths (HPCDCM) were prepared by selective

extraction of silicon from ordered mesoporous silicon carbide monoliths (OMSCM) through

chlorination at high temperature. The OMSCM was firstly synthesized by pressure-assisted

nanocasting procedure using KIT-6 silica as the hard template and polycarbosilane (PCS-800) as the

preceramic precursor. The OMSCM showed cubic ordered mesoporous structure with specific surface

area of over 600 m2 g�1. After the chlorination, the resulting HPCDCM demonstrated very high

specific surface area (2933 m2 g�1), large pore volume (2.101 cm3 g�1) with large volume of micropores

(0.981 cm3 g�1), and narrow dual pore size distributions (micropore: 0.9 nm, and mesopore: 3.1 nm).

Macropores in the micron range were observed in the HPCDCM. The mesostructural ordering was not

maintained in the HPCDCM and the volume of the HPCDCMhad greatly shrunk, by 21.2% compared

to that of the OMSCM, but the tablet-like appearance was well retained in the HPCDCM. At�196 �C,the HPCDCM shows good hydrogen uptakes of 2.4 wt% and 4.4 wt% at 1 bar and 36 bar, respectively.

The calculated volumetric hydrogen storage capacity is 11.6 g L�1 at 36 bar. The gravimetric hydrogen

uptake capacity of the HPCDCM is comparable to, or higher than, those of previously reported

ordered mesoporous carbide-derived carbon (CDC) powder and microporous CDC powder.

1. Introduction

Porous carbon materials with high surface areas and uniform

pore size distributions have received increasing attention in

various applications, such as gas adsorbents,1–3 bioimaging,4

catalytic supports,5,6 the electrode materials in various electro-

chemical devices,7,8 etc.,9,10 because they have the significant

advantages of wide availability, adjustable microstructure, low-

cost, high chemical and thermal stability, and many variable

forms.11 Till now, much effort has been made to synthesize and

tailor the microstructure of porous carbon materials by using

various solid, liquid and gaseous precursors via various syntheses

and activation procedures, such as the template method,11

chemical activation,12 physical activation,12 etc. Templated

porous carbons, normally synthesized using a ‘‘hard template’’ or

‘‘soft template’’ method, show well-controlled pore size distri-

bution, and an interconnected pore structure.11,13 Various

chemical and physical activation procedures have been applied in

industry to prepare activated carbons with high surface areas.12,14

Department of Inorganic Chemistry, Dresden University of Technology,Bergstrasse-66, 01069 Dresden, Germany. E-mail: [email protected]; Fax: +49 351 46337287; Tel: +49 351 46334885

† Electronic supplementary information (ESI) available. See DOI:10.1039/c2jm34472f

This journal is ª The Royal Society of Chemistry 2012

CDCs, prepared through the selective etching of metal

carbides (e.g. SiC, TiC, and ZrC) using chlorine at high

temperatures, have narrow pore size distributions, large pore

volumes, and high surface areas of up to 3000 m2 g�1.15,16 The

reaction proceeds as shown in eqn (a). The metal element is

removed in the form of gaseous MCl4, and solid carbon remains.

The microstructure of the resulting CDC materials totally

depends on both different metal carbide precursors and various

chlorination parameters, such as temperature, time, etc.

MC (s) + 2Cl2 (g) / MCl4 (g) + C (s) (a)

Generally, the chlorination of various non-porous metal

carbide precursors leads to microporous CDC materials with

random pore orientation.16–21 Microporous CDC materials

exhibit great potential for hydrogen storage,18,19 the electrode

materials in supercapacitors,16,20,22 and catalytic supports.23,24

Introduction of uniform mesopores into CDC materials by a

two-stage synthetic procedure resulted in bimodal micro-meso-

porous CDCs in our group. Firstly, ordered mesoporous SiC was

produced from liquid preceramic precursors (PCS-800 and

SMPT-10) by the nanocasting method, in which various ordered

mesoporous silicas (SBA-15 and KIT-6) were used as hard

templates.25,26 The ordered mesoporous SiC ceramics obtained

were further transformed into ordered mesoporous CDC

(OM-CDC) by chlorination at high temperatures.27–31 OM-CDC

J. Mater. Chem., 2012, 22, 23893–23899 | 23893

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materials demonstrated larger pore volume and higher surface

area compared to those of microporous CDC materials prepared

by chlorination of non-porous SiC.28 Thus, OM-CDC materials

showed better performances for hydrogen storage and electrode

materials in supercapacitors. For example, the surface area of

OM-CDC (2200–2600 m2 g�1) are evidently higher than that of

microporous CDC (1578 m2 g�1), both of which were chlorinated

under the same parameters.28 The saturated hydrogen excess

storage capacities (48–51 mg g�1) of OM-CDC materials were

higher than those (39 mg g�1) of microporous CDCs.28

For practical applications, shaping of porous solids is an

essential processing step. For gas storage applications, monoliths

are ideally suited. However, an essential requirement is the

integration of transport pores in monoliths in order to allow

rapid diffusion.

Recently, Gogotsi and co-workers reported the synthesis of

monolithic CDCs and CDC film by the extraction of the titanium

element in full density titanium carbide (TiC) ceramics and film,

respectively.32–34 These monolithic microporous CDCs have a

moderate surface area of 1600 m2 g�1 and a pore volume of up to

0.9 cm3 g�1.33 Herein, we report a synthetic procedure for hier-

archical porous CDC monolith (HPCDCM) through chlorina-

tion of ordered mesoporous SiC monolith (OMSCM). The

OMSCMwas first produced by the pressure-assisted nanocasting

method, using polycarbosilane precursor PCS-800 and KIT-6

silica as the hard template. The OMSCM has tablet-like

morphology and shows high surface area of 642 m2 g�1, uniform

mesopore size distribution (3.1 nm), and cubic ordered meso-

porous structure. The selective etching of silicon in the OMSCM

at high temperature causes the formation of the HPCDCM, with

well retained tablet-like morphology. As far as we know, this is

the first time a mesoporous SiC monolith has been successfully

transformed to a bimodal CDC monolith.35 The gravimetric

hydrogen uptake capacity of the HPCDCM is comparable to, or

higher than, those of previously reported OM-CDC powder and

microporous CDC powder. Thus, this HPCDCM with regular

bulky morphology can be expected to replace CDC powders as

the storage media for H2.

2. Experimental section

2.1 Material synthesis

Synthesis of KIT-6 silica.36 33.3 g of triblock copolymer Pluronic

P123 (EO20PO70EO20, Aldrich) was dissolved in 1204 g of

deionized water and 65.8 g of concentrated HCl (37%), and

stirred overnight at 35 �C. To this solution 33.3 g of butanol was

added under stirring at 35 �C. After 1 h, 71.67 g of tetraethyl

orthosilicate (TEOS) were quickly added and stirred for 24 h at

35 �C. The milky suspension was transferred to an autoclave and

annealed at 130 �C for 24 h. The white solid was filtered, washed

using an ethanol–water mixture (1 : 1 volume), and then calcined

at 550 �C for 5 h in air.

Synthesis of OMSCM. Typically, 2 g of as-prepared KIT-6

was added to the solution containing 2.96 g of PCS-800

(Aldrich), 40 g of n-heptane, and 1.8 g of 1-butanol. The resulting

mixture was vigorously stirred in an open beaker for the evap-

oration of the solvents at room temperature, until a white dry

powder was obtained. Subsequently, the resulting powder was

23894 | J. Mater. Chem., 2012, 22, 23893–23899

thoroughly mixed with 10 wt% of P123, as the binder, using a

mortar and pestle. Then, the composite powder containing the

binder was pressed into PCS-800/KIT-6 tablet-like monoliths

(�0.3 g per piece) with a diameter of 10 mm at a compression

force of 20 kN. These fresh monoliths were heated in an alumina

tube furnace under an argon flow to decompose the binder and

pyrolyze the preceramic precursor PCS-800 according to the

following temperature program: room temperature to 350 �C at

120 �C h�1, then 5 h at 350 �C; 350–700 �C at 60 �C h�1; and 700–

1000 �C at 150 �C h�1, then 2 h at 1000 �C. After cooling to room

temperature, the resulting SiC/KIT-6 composite monoliths were

immersed in 40% HF solution for 1 week to etch the silica

framework, followed by washing with ethanol and then drying at

80 �C to obtain OMSCM.37

Synthesis of HPCDCM. HPCDCM was prepared by direct

chlorination of OMSCM using chlorine to remove silicon at high

temperature. Several pieces of OMSCM were heated in a quartz

boat inside a horizontal quartz tube furnace under an argon flow.

When the temperature reached to 800 �C, chlorine was intro-

duced for 40 min while argon was kept at the same level. After

that time, chlorine was shut off and the furnace cooled down to

room temperature under an argon flow.

2.2 Material characterization

Small-angle X-ray diffraction (XRD) experiments were per-

formed on a Bruker Nanostar (sealed tube, Cu Ka1; l ¼ 0.15406

nm) with a position sensitive Histar 2D detector. Transmission

electron microscopy (TEM) investigations were performed using

a 200 kV TEM FEI Tecnai T20 instrument. Scanning electron

microscopy (SEM) coupled with energy dispersive X-ray analysis

(EDX) was performed on a ‘DSM-982 Gemini’ using a back-

scattered electron detector from Zeiss. Prior to all adsorption

measurements, the samples were degassed overnight at 150 �Cusing the evacuation equipment of the adsorption devices.

Nitrogen sorption isotherms were collected at �196 �C using a

Quantachrome Autosorb 1C apparatus. Specific surface areas

were calculated using the Brunauer–Emmett–Teller (BET)

equation (p/p0 ¼ 0.05–0.2). The pore size distributions were

determined by the non-local density functional theory (NLDFT)

or quenched solid density functional theory (QSDFT) method

using the equilibrium model. The total pore volume was deter-

mined at relative pressure p/p0 ¼ 0.98. Thermogravimetric

analysis (TGA) was performed using a Netzsch STA-409

instrument. Micro-Raman spectroscopy was performed using a

laser wavelength of 785 nm on a Hololab Series 5000 research

spectrometer (Kaiser Optical Systems) equipped with a 100�objective. The laser was operated at 5 mW. The spectrum was

obtained in ten accumulations with 60 s and the extended regime

in the range is 800–1800 cm�1.

2.3 Hydrogen storage measurements at ambient and high

pressure

Before measurements, the sample was degassed at 150 �Cin vacuum overnight. Hydrogen physisorption isotherms at

�196 �C and ambient pressure were collected using a Quan-

tachrome Autosorb 1C apparatus.

This journal is ª The Royal Society of Chemistry 2012

Table 1 Shape parameters and volume reduction of the monoliths

SampleDiameter(mm)

Thickness(mm)

Volume(mm3) DVa (%)

PCS-800/KIT-6 10 3.1 243.4 —SiC/KIT-6 8.9 2.9 180.3 25.9OMSCM 8.9 2.9 180.3 25.9HPCDCM 8.1 2.5 128.7 47.1

a DV is the volume reduction (%) of the monoliths compared to the

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High pressure hydrogen adsorption measurement was per-

formed at �196 �C up to 100 bar on about 0.2 g sample. A high

pressure volumetric BELSORP-HP apparatus was used to

quantify the Gibbs excess amount of hydrogen adsorbed. The

total volume of the empty vessel was determined via helium

measurement at 25 �C and �196 �C. On the supposition that

helium does not adsorb at 25 �C, the sample volume and so-

called helium density of the sample were determined via helium

measurement.

3. Results and discussion

The polycarbosilane precursor PCS-800 was introduced into the

mesopores of KIT-6 silica using wet impregnation in heptane/

butanol.27 After the evaporation of solvents at room tempera-

ture, the resulting PCS-800/KIT-6 composite powder was

pressed into the tablet-like monoliths with the addition of P123

as the binder, as shown in Fig. 1a. The freshly pressed monoliths

were heated in an argon atmosphere to decompose P123 binder

and pyrolyze PSC-800 at 1000 �C. This pyrolysis process

produced the SiC/KIT-6 monoliths with retention of the tablet-

like morphology, as presented in Fig. 1b. Following the pyrolysis

step, the SiC/KIT-6 monoliths were immersed in HF solution to

remove KIT-6 silica framework. Fig. 1c shows a photograph of

the resulting OMSCM, confirming that the monolithic tablet-like

morphology is well retained without the KIT-6 silica template.

The OMSCM was then used as the precursor to prepare the

HPCDCM by chlorination to remove silicon at 800 �C. A

photograph of the obtained HPCDCM in Fig. 1d indicates

maintenance of the good tablet-like appearance. No cracks were

found in these monoliths by the naked eye. All monoliths dis-

cussed in this paper have a good tablet-like appearance as

depicted in Fig. 1.

The shape parameters and volumes of various tablet-like

monoliths are listed in Table 1. The as-pressed PCS-800/KIT-6

monolith is 10 mm in diameter and 3.1 mm in thickness. Pyrol-

ysis at 1000 �C resulted in the evident reduction from 10 to 8.9

mm in diameter and from 3.1 to 2.9 mm in thickness, and the

total volume reduction for the SiC/KIT-6 monolith is �25.9%

compared to that of the fresh PCS-800/KIT-6 monolith. This

volume reduction is mainly ascribed to the additional shrinkage

Fig. 1 Digital camera photographs of the as-prepared PCS-800/KIT-6

monolith (a), SiC/KIT-6 monolith (b), OMSCM (c), and HPCDCM (d).

This journal is ª The Royal Society of Chemistry 2012

of the KIT-6 silica framework when exposed to a higher

temperature (1000 �C) than the calcination temperature (550 �C)when preparing KIT-6. The removal of the KIT-6 silica frame-

work did not change the appearance and size of the resultant

OMSCM. An evident reduction in volume occurred when

removing silicon from the OMSCM by chlorination. The

resulting HPCDCM is 8.1 mm in diameter and 2.5 mm in

thickness, and the total volume reduces by �47.1% compared to

that of the PCS-800/KIT-6 monolith. Compared to that of the

OMSCM, the volume of HPCDCM is also greatly reduced by

21.2%, because of the removal of silicon in the OMSCM

framework. The original OMSCM had robust mechanical

stability. Both the OMSCM and HPCDCM can be easily

handled for further characterizations.

To confirm the complete removal of silicon from the bulk

OMSCM after chlorination, the thermogravimetry-differential

thermogravimetry (TG-DTG) measurement was performed on

the HPCDCM in an air flow. As shown in Fig. 2, there are two

main weight loss stages in the TG curve. The first stage of weight

loss, ascribed to the desorption of the adsorbed moisture, is �17

wt% between room temperature and 140 �C. The DTG curve

shows an evident valley with a maximum located at �93 �C. Thesecond weight loss of�82% with a valley at about�621 �C in the

DTG curve took place between 400 and 750 �C, which was the

result of combusting carbon in air.38 At 750 �C, the residual mass

was below 1 wt%. However TG showed that the bulk OMSCM

retained about 82% mass at 800 �C (Fig. S1, ESI†). These results

suggest that the silicon in the monolith had been essentially

Fig. 2 TG and DTG curves of the HPCDCM in an air flow

(10 �C min�1).

J. Mater. Chem., 2012, 22, 23893–23899 | 23895

Fig. 3 Small-angle XRD patterns of KIT-6 silica (a), SiC/KIT-6

monolith (b), OMSCM (c), and HPCDCM (d).

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totally removed by chlorination using chlorine at high temper-

ature. It also implies that the KIT-6 silica framework in the

OMSCM was completely etched off by HF solution.

The mesostructural ordering of the KIT-6 template and the

monoliths was investigated by small-angle XRD measurements.

The d211 values and lattice parameters are listed in Table 2. As

shown in Fig. 3a, the small-angle XRD pattern of KIT-6 silica

has the well-defined (211) and (220) diffractions implying good

three-dimensional (3D) bi-continuous cubic structure (Ia3d).36

Pyrolysis of the PCS-800/KIT-6 monolith at 1000 �C resulted in

the (211) diffraction shifting to higher angle (Fig. 3b). As a result,

the corresponding d211-spacing (10.0 nm) and lattice parameter

(24.4 nm) of KIT-6 silica decreased to 8.7 nm and 21.2 nm,

respectively, for the SiC/KIT-6 monolith due to the high

temperature induced framework contraction on KIT-6 silica,

thus resulting in the evident volume reduction of the SiC/KIT-6

monolith. After removing the KIT-6 silica framework in the SiC/

KIT-6 monolith, the mesostructural ordering of the resulting

OMSCM replica was still retained, as determined by small-angle

XRD (Fig. 3c), showing a single characteristic diffraction peak

(211). The lack of the evident (220) diffraction indicates the low

long-range ordering in the OMSCM. The d211-spacing and lattice

parameter of the OMSCM is �8.7 and 21.2 nm, respectively, the

same as those of the SiC/KIT-6 monolith. Unfortunately, the

chlorination of the OMSCM produced HPCDCM with the loss

of the mesostructural ordering, as confirmed in Fig. 3d, and no

peak is found in the small angle region. It is believed that the

ordered mesoporous framework in the monolith distorted,

collapsed, and was re-constructed during the high temperature

chlorination to remove the silicon element for the in situ trans-

formation of SiC to carbon. As a result, the mesostructural

ordering disappeared in the HPCDCM. This result is consistent

with those reported for porous CDC powders prepared by

chlorination of PCS-derived OM-SiC powders.27,29

The porosities of KIT-6 silica and various monoliths were

determined by nitrogen adsorption measurements. The textural

properties obtained for KIT-6 silica and the monoliths are pre-

sented in Table 2. The nitrogen adsorption isotherms and pore

size distribution curves are shown in Fig. 4. The nitrogen

adsorption isotherm for KIT-6 silica as the hard template is of

type IV, with a sharp capillary condensation step at relatively

high pressure (0.7–0.85) and H1 hysteresis loop, indicative of

large channel-like mesopores. KIT-6 silica has a high specific

surface area of 609 m2 g�1, large pore volume of 1.345 cm3 g�1,

and narrow pore size distribution of 9.5 nm. After pyrolysis of

the PCS-800/KIT-6 monolith, the resulting SiC/KIT-6 monolith

exhibited a very low uptake of nitrogen in the adsorption

Table 2 Textural properties of KIT-6 silica and various monoliths

Sample d211a [nm] a0

b [nm] SBET [m2 g�1]

KIT-6 10.0 24.4 609SiC/KIT-6 8.7 21.2 293OMSCM 8.7 21.2 642HPCDCM — — 2933

a d211 ¼ 0.15406/(2sin q). b The unit cell parameter a0 calculated by using thequilibrium model with cylindrical pores for KIT-6 and slit/cylindrical porewith slit pores for OMSCM, and HPCDCM. d Total pore volume calculated

23896 | J. Mater. Chem., 2012, 22, 23893–23899

isotherm. The surface area decreased by more than 50% and the

total pore volume was only �12% that of KIT-6 silica. No

mesopores were observed in the SiC/KIT-6 monolith. All these

results are clear indications of effectively filling the mesopores of

KIT-6 with SiC. The OMSCM exhibited an enhanced nitrogen

uptake, surface area (642 m2 g�1) and pore volume (0.535 cm3

g�1), which were greatly increased in comparison to those of the

SiC/KIT-6 monolith, due to the removal of the silica template.

There are three peaks at ca. 3.10, 1.85, and 0.96 nm in the pore

size distribution curve of the OMSCM monolith. The existence

of microporosity (0.134 cm3 g�1) in the OMSCM was mainly

attributed to micropores present within the replicated SiC rods,

which could arise due to non-uniform shrinkage during the

pyrolysis of PCS-800.

As shown in Fig. 4, the HPCDCM prepared by removing the

silicon in the OMSCM via chlorination demonstrated a very high

uptake of nitrogen and the adsorption isotherm is type IV with a

H1 hysteresis loop at the relative pressure range of 0.5–0.8,

typical of mesoporous material. The hysteresis loop does not

close at higher relative pressure (p/p0 ¼ 0.8–1.0), which might be

a result of interparticle textural pores in the HPCDCM. The

surface area (2933 m2 g�1) and pore volume (2.101 cm3 g�1) of

the HPCDCM are significantly increased compared to those of

the OMSCM. Nanopores with a size lower than 5 nm contribute

to the vast majority of porosity in the HPCDCM (Fig. S2, ESI†).

These values are also far higher than those of monolithic CDC

bulky materials and CDC film.32–34 The mesopore size of the

Vmicroc [cm3 g�1] Vtotal

d [cm3 g�1] Dmesoc [nm]

0.003 1.345 9.50.050 0.161 2.5–3.60.134 0.535 3.10.981 2.101 3.1

e formula a0 ¼ d211 � 61/2. c Determined by the NLDFT method usings for SiC/KIT-6, and by the QSDFT method using equilibrium modelat p/p0 ¼ 0.98.

This journal is ª The Royal Society of Chemistry 2012

Fig. 4 N2 adsorption–desorption isotherms (a) and pore size distribu-

tion curves (b) of KIT-6, SiC/KIT-6 monolith, OMSCM, and

HPCDCM.

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HPCDCM is 3.1 nm, exactly the same as that of the OMSCM,

which implied that chlorination could not change the textural

mesopore sizes in the OMSCM. However the total volume of the

HPCDCM decreased by 21.2% compared to that of the

OMSCM. Thus, this reduction is certainly due to the framework

contraction resulting from the in situ transformation of SiC to

carbon. An evident micropore size of �0.9 nm and high micro-

pore volume (0.981 cm3 g�1) are also obtained in the HPCDCM.

The high specific surface area and large pore volume with a large

portion of micropore volume in the HPCDCM are beneficial for

its application in gas storage.

The morphologies of the particles obtained from deliberately

crushing the monoliths were collected by SEM. As presented in

Fig. 5a and b, the particles from the OMSCM show a bulky

structure containing some small particles and no pores could be

found. After the transformation of the OMSCM to HPCDCM

by chlorination, lots of large to small irregular particles with

smooth surfaces generated by crushing the HPCDCM are

observed in Fig. 5c and d. This observation is consistent with the

monolithic morphology from which the particles are derived.39

At the same time, slit macropores of �1 mm in width appeared in

the HPCDCM, possibly due to the evident framework contrac-

tion when chlorinating SiC to carbon.33 These slit macropores

Fig. 5 SEM images of the OMSCM (a and b) and HPCDCM (c and d).

This journal is ª The Royal Society of Chemistry 2012

formed in the HPCDCM are advantageous for the diffusion of

various gases and organic molecules into the mesopores and

micropores. EDX detected the existence of chlorine with �4.3

wt% in the HPCDCM. The existence of chlorine is observed in

various CDC powders prepared by chlorination of carbides with

chlorine at high temperature.

The microstructure of the OMSCM and HPCDCM was

further confirmed by TEM. As shown in Fig. 6a and b, some

circular and stripe-like patterns were observed in the TEM

images of the OMSCM, implying the replication of an ordered

pore structure in the OMSCM after the removal of the silica

template. This result matches well with the small-angle XRD

analysis. Transformation of the OMSCM to HPCDCM by

chlorination resulted in the non-ordered pore structure as shown

in Fig. 6c, although unclear stripes could be observed in some

regions, confirmed by high resolution TEM image (Fig. 6d).

TEM images also indicate that the uniform mesopore size

distribution is well retained, which is necessary for high meso-

porosity in the HPCDCM. This result is consistent with that of

nitrogen adsorption measurement.

In the Raman spectrum of the HPCDCM shown in Fig. 7, two

broad peaks are observed. One peak at �1300 cm�1 is indicative

of the D band of disordered carbon, and another one at �1600

cm�1 is ascribed to the G-band deriving from graphitic

carbon.28,30,31 The larger ratio of the D-band and G-band

intensities (ID/IG) is consistent with carbon microstructural dis-

ordering and more defects in carbon materials.40 This ID/IGrelative ratio is typical for porous carbons with high degree of

structural disorder, correlating well with the previously reported

amorphous carbons and other CDC materials.30,41–43 This is also

in agreement with the formation of amorphous carbon structure

as observed by TEM measurements.

The hydrogen physisorption isotherm of the HPCDCM up to

1 bar at �196 �C is shown in Fig. 8a. A hydrogen uptake of

�24 mg g�1 is obtained in the HPCDCM at 1 bar. This hydrogen

uptake value is comparable to the previously reported values for

OM-CDC28 and microporous CDC powders.18 The hydrogen

storage capacity of the HPCDCM was also investigated by high

pressure hydrogen adsorption measurement over the pressure

Fig. 6 TEM images of the OMSCM (a and b) and HPCDCM (c and d).

J. Mater. Chem., 2012, 22, 23893–23899 | 23897

Fig. 7 Raman spectrum of the HPCDCM.

Fig. 8 The volumetric hydrogen measurements at �196 �C of the

HPCDCM at ambient pressure (a) and high pressure (b).

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range of 0–100 bar at �196 �C. As shown in Fig. 8b, it can be

observed that the desorption isotherm is very consistent with the

adsorption isotherm, and no hysteresis is formed in the isotherm.

This result shows that storage of hydrogen in the HPCDCM is

totally reversible. The corresponding maximum Gibbs excess

amount adsorbed is 44 mg H2 g�1 at 36 bar. The bulk density of

the HPCDCM is calculated to be 0.264 g cm�3, and thus the

corresponding volumetric hydrogen storage of 11.6 g L�1 for the

HPCDCM can be estimated. The gravimetric hydrogen storage

capacity of the HPCDCM is only a little lower than that previ-

ously reported for OM-CDC powder prepared by chlorination of

SBA-15 templated ordered mesoporous SiC powders (hydrogen

uptake: 48–52 mg g�1).28 Based on the hydrogen uptakes at

ambient and high pressures, this implies that OM-CDC in

monolithic form has comparable performance to the powder,

which is an excellent result. Furthermore, the excess hydrogen

uptake of the HPCDCM is higher than that (39.3 mg H2 g�1) of

microporous CDC powder because of the higher surface area

and larger pore volume of the HPCDCM.28 Moreover, the

hydrogen storage capacities of ordered mesoporous carbons

prepared using mesoporous silica MCM-48 and SBA-15 as the

23898 | J. Mater. Chem., 2012, 22, 23893–23899

hard template are 2.7 wt% (�196 �C and 60 bar)44 and 2.9 wt%

(�196 �C and 30 bar),28 respectively, which are evidently lower

than our reported value for the HPCDCM.

4. Conclusions

We have reported for the first time that a HPCDCM was

prepared by selective extraction of silicon in OMSCM through

chlorination using chlorine at high temperature. The OMSCM

was synthesized by a pressure-assisted nanocasting procedure

using KIT-6 silica as the hard template and polycarbosilane

(PCS-800) as the preceramic precursor. The OMSCM showed a

cubic ordered mesoporous structure with specific surface area of

over 600 m2 g�1. The tablet-like morphology of the OMSCM is

generally retained after chlorination to generate the HPCDCM,

but the volume of the HPCDCM evidently decreases by 21.2%

compared to that of the OMSCM. The formation of macropores

in the micron range is observed in the HPCDCM because of this

shrinkage. TGA indicated that silicon from both SiC and KIT-6

silica template was completely removed in the HPCDCM. The

resulting HPCDCM demonstrated very high specific surface area

(2933 m2 g�1), large pore volume (2.101 cm3 g�1) with large

volume of micropores (0.981 cm3 g�1), and narrow dual pore size

distributions (micropore: 0.9 nm, and mesopore: 3.1 nm). The

mesostructural ordering was not maintained in the HPCDCM,

and TEM images showed the existence of uniform mesopores in

the HPCDCM. The HPCDCM exhibited a good hydrogen

uptake of 2.4 wt% at �196 �C and 1 bar. At high pressure, a

saturated hydrogen uptake of up to 4.4 wt% was obtained at 36

bar and �196 �C, and the calculated volumetric hydrogen

storage capacity is 11.6 g L�1. The gravimetric hydrogen uptake

of the HPCDCM is comparable to, or higher than, those of the

previously reported OM-CDC powder, microporous CDC

powder, and mesoporous silica templated porous carbons.

Acknowledgements

J.W. thanks the Alexander von Humboldt Foundation for

granting him a research fellowship. The authours are highly

thankful to Dr Susanne Machill for performing Raman

experiment.

Notes and references

1 R. E. Morris and P. S. Wheatley, Angew. Chem., Int. Ed., 2008, 47,4966.

2 Q. Wang, J. Luo, Z. Zhong and A. Borgna, Energy Environ. Sci.,2011, 4, 42.

3 J. Wang, A. Heerwig, M. R. Lohe, M. Oschatz, L. Borchardt andS. Kaskel, J. Mater. Chem., 2012, 22, 13911.

4 S. Yang, H. Zeng, H. Zhao, H. Zhang and W. Cai, J. Mater. Chem.,2011, 21, 4432.

5 J. Biener, M. Stadermann, M. Suss, M. A. Worsley, M. M. Biener,K. A. Rose and T. F. Baumann, Energy Environ. Sci., 2011, 4, 656.

6 S. H. Joo, S. J. Choi, I. Oh, J. Kwak, Z. Liu, O. Terasaki and R. Ryoo,Nature, 2001, 412, 169.

7 Y. Zhai, Y. Dou, D. Zhao, P. F. Fulvio, R. T. Mayes and S. Dai, Adv.Mater., 2011, 23, 4828.

8 J. C. Wang and S. Kaskel, J. Mater. Chem., 2012, DOI: 10.1039/c2jm34066f.

9 M. E. Davis, Nature, 2002, 417, 813.10 J. Wang, X. Yu, Y. Li and Q. Liu, J. Phys. Chem. C, 2007, 111, 18073.11 J. Lee, J. Kim and T. Hyeon, Adv. Mater., 2006, 18, 2073.

This journal is ª The Royal Society of Chemistry 2012

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1039

/C2J

M34

472F

View Online

12 H.Marsh and F. R. Reinoso,Activated Carbon, Elsevier, Amsterdam,2006.

13 Y. Xia, Z. Yang and R. Mokaya, in Porous Materials, John Wiley &Sons, Ltd, 2010, p. 217.

14 T. Otowa, R. Tanibata and M. Itoh, Gas Sep. Purif., 1993, 7, 241.15 V. Presser, M. Heon and Y. Gogotsi, Adv. Funct. Mater., 2011, 21,

810.16 R. Dash, J. Chmiola, G. Yushin, Y. Gogotsi, G. Laudisio, J. Singer,

J. Fischer and S. Kucheyev, Carbon, 2006, 44, 2489.17 Y. Gogotsi, A. Nikitin, H. H. Ye, W. Zhou, J. E. Fischer, B. Yi,

H. C. Foley and M. W. Barsoum, Nat. Mater., 2003, 2, 591.18 Y. Gogotsi, R. K. Dash, G. Yushin, T. Yildirim, G. Laudisio and

J. E. Fischer, J. Am. Chem. Soc., 2005, 127, 16006.19 G. Yushin, R. Dash, J. Jagiello, J. E. Fischer and Y. Gogotsi, Adv.

Funct. Mater., 2006, 16, 2288.20 J. Chmiola, G. Yushin, R. Dash and Y. Gogotsi, J. Power Sources,

2006, 158, 765.21 I. Tallo, T. Thomberg, K. Kontturi, A. J€anes and E. Lust, Carbon,

2011, 49, 4427.22 C. Portet, M. A. Lillo-Rodenas, A. Linares-Solano and Y. Gogotsi,

Phys. Chem. Chem. Phys., 2009, 11, 4943.23 A. Schlange, A. R. dos Santos, B. Hasse, B. J. M. Etzold, U. Kunz

and T. Turek, J. Power Sources, 2012, 199, 22.24 L. Borchardt, F. Hasch�e, M. R. Lohe, M. Oschatz, F. Schmidt,

E. Kockrick, C. Ziegler, T. Lescouet, A. Bachmatiuk, B. B€uchner,D. Farrusseng, P. Strasser and S. Kaskel, Carbon, 2012, 50, 1861.

25 P. Krawiec, C. Schrage, E. Kockrick and S. Kaskel, Chem. Mater.,2008, 20, 5421.

26 P. Krawiec, D. Geiger and S. Kaskel, Chem. Commun., 2006, 2469.27 M. Oschatz, E. Kockrick, M. Rose, L. Borchardt, N. Klein,

I. Senkovska, T. Freudenberg, Y. Korenblit, G. Yushin andS. Kaskel, Carbon, 2010, 48, 3987.

28 E. Kockrick, C. Schrage, L. Borchardt, N. Klein, M. Rose,I. Senkovska and S. Kaskel, Carbon, 2010, 48, 1707.

This journal is ª The Royal Society of Chemistry 2012

29 P. Krawiec, E. Kockrick, L. Borchardt, D. Geiger, A. Corma andS. Kaskel, J. Phys. Chem. C, 2009, 113, 7755.

30 Y. Korenblit, M. Rose, E. Kockrick, L. Borchardt, A. Kvit, S. Kaskeland G. Yushin, ACS Nano, 2010, 4, 1337.

31 M. Rose, Y. Korenblit, E. Kockrick, L. Borchardt, M. Oschatz,S. Kaskel and G. Yushin, Small, 2011, 7, 1108.

32 J. Chmiola, C. Largeot, P.-L. Taberna, P. Simon and Y. Gogotsi,Science, 2010, 328, 480.

33 S.-H. Yeon, I. Knoke, Y. Gogotsi and J. E. Fischer, MicroporousMesoporous Mater., 2010, 131, 423.

34 M. Heon, S. Lofland, J. Applegate, R. Nolte, E. Cortes,J. D. Hettinger, P.-L. Taberna, P. Simon, P. Huang, M. Brunet andY. Gogotsi, Energy Environ. Sci., 2011, 4, 135.

35 M. Oschatz, L. Borchardt, M. Thommes, K. A. Cychosz,I. Senkovska, N. Klein, R. Frind, M. Leistner, V. Presser,Y. Gogotsi and S. Kaskel, Angew. Chem., Int. Ed., 2012, 51, 7577.

36 F. Kleitz, S. H. Choi and R. Ryoo, Chem. Commun., 2003, 2136.37 J. Wang, M. Oschatz, T. Biemelt, M. R. Lohe, L. Borchardt and

S. Kaskel, Microporous Mesoporous Mater., 2012, DOI: 10.1016/j.micromeso.2012.09.037.

38 J. Wang and Q. Liu, J. Phys. Chem. C, 2007, 111, 7266.39 B. H. Han, W. Zhou and A. Sayari, J. Am. Chem. Soc., 2003, 125,

3444.40 A. C. Ferrari and J. Robertson, Phys. Rev. B: Condens. Matter, 2000,

61, 14095.41 S. Urbonaite, L. H€alldahl and G. Svensson, Carbon, 2008, 46,

1942.42 L. Wei, M. Sevilla, A. B. Fuertes, R. Mokaya and G. Yushin, Adv.

Funct. Mater., 2012, 22, 827.43 Z. G. Cambaz, G. N. Yushin, Y. Gogotsi, K. L. Vyshnyakova and

L. N. Pereselentseva, J. Am. Ceram. Soc., 2006, 89, 509.44 E. Terr�es, B. Panella, T. Hayashi, Y. A. Kim, M. Endo,

J. M. Dominguez, M. Hirscher, H. Terrones and M. Terrones,Chem. Phys. Lett., 2005, 403, 363.

J. Mater. Chem., 2012, 22, 23893–23899 | 23899