Chemically activated fungi-based porous carbons for hydrogen storage

This article appeared in a journal published by Elsevier. The attachedcopy is furnished to the author for internal non-commercial researchand education use, including for instruction at the authors institution

and sharing with colleagues.

Other uses, including reproduction and distribution, or selling orlicensing copies, or posting to personal, institutional or third party

websites are prohibited.

In most cases authors are permitted to post their version of thearticle (e.g. in Word or Tex form) to their personal website orinstitutional repository. Authors requiring further information

regarding Elsevier’s archiving and manuscript policies areencouraged to visit:

http://www.elsevier.com/authorsrights

Author's personal copy

Chemically activated fungi-based porous carbonsfor hydrogen storage

Jiacheng Wang a,*, Irena Senkovska b, Stefan Kaskel b, Qian Liu a

a State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Shanghai 200050,

PR Chinab Department of Inorganic Chemistry, Dresden University of Technology, Bergstraße 66, 01069 Dresden, Germany

A R T I C L E I N F O

Article history:

Received 24 November 2013

Accepted 3 April 2014

Available online 13 April 2014

A B S T R A C T

A set of porous carbons has been prepared by chemical activation of various fungi-based

chars with KOH. The resulting carbon materials have high surface areas (1600–2500 m2/g)

and pore volumes (0.80–1.56 cm3/g), regardless of the char precursors. The porosities

mainly derived from micropores in activated carbons strongly depend on the activation

parameters (temperature and KOH amount). All activated carbons have uniform microp-

ores with pore size of 0.8–0.9 nm, but some have a second set of micropores (1.3–1.4 nm

pore size), further broadened to 1.9–2.1 nm as a result of increasing either the activation

temperature to 750 �C or KOH/char mass ratio to 5/1. These fungi-based porous carbons

achieve an excellent H2 uptake of up to 2.4 wt% at 1 bar and �196 �C, being in agreement

with results from other porous carbonaceous adsorbents reported in the literature. At high

pressure (ca. 35 bar), the saturated H2 uptake reaches 4.2–4.7 wt% at �196 �C for these

fungi-based porous carbons. The results imply a great potential of these fungi-based

porous carbons as H2 on-board storage media.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Various carbon nanostructured materials, ranging from three-

dimensional porous carbons [1] and one-dimensional (1D)

carbon nanotubes (CNTs) to two-dimensional (2D) graphene

nanosheets [2], have received increasing attention in various

fields [3,4]. Because of their high surface areas, large pore vol-

umes, adjustable porosities, low-cost, and ease of processing,

porous carbons with high surface areas and uniform pore size

distributions are particularly focused on and have extensively

studied in many aspects such as CO2 capture [5–9], catalysis

[10,11], gas adsorption/separation [12–14], energy storage

[14–18], water purification [19,20], electromagnetic interfer-

ence/shielding [21–24], etc. Moreover, porous carbon materials

have also been explored as on-board storage media for H2

energy [25,26], a sustainable future energy system [27,28].

To solve increasing environmental pollution, global

climate warming, and energy crisis resulting from the

combustion of fossil fuels, H2 energy as a clean, sustainable,

renewable energy supply has been regarded as a highly prom-

ising alternative for fossil fuels. However one of the main

challenges for on-board use of H2 energy lie in highly efficient

H2 storage [29]. Among current H2 storage technologies, the

physisorption using high-surface-area porous carbons is par-

ticularly useful. Compared to chemical storage of H2 by metal

hydrides, which have some drawbacks including inherent

slow kinetics and thermodynamic energy inefficiency [30],

H2 storage using porous carbons as solid physisorbents has

http://dx.doi.org/10.1016/j.carbon.2014.04.0160008-6223/� 2014 Elsevier Ltd. All rights reserved.

* Corresponding author.E-mail address: [email protected] (J. Wang).

C A R B O N 7 5 ( 2 0 1 4 ) 3 7 2 – 3 8 0

Avai lab le at www.sc iencedi rect .com

ScienceDirect

journal homepage: www.elsev ier .com/ locate /carbon

Author's personal copy

evident advantages such as fast adsorption kinetics and low

energy cost. The H2 uptake capacities of porous carbons are

highly correlated to specific surface areas and pore sizes,

and the optimum pore size for H2 adsorption is ca. 0.7 nm,

which is very effective for strengthening H2-adsorbent inter-

actions [31–34]. Till now, various procedures including the

template method [35], the physical activation, and the chem-

ical activation [36] have been adopted to prepare highly por-

ous carbons. Especially, the porous carbons prepared by

KOH activation have very high specific surface area, large pore

volume, and well-defined micropore size distribution (<1 nm)

[15,37], which are suitable for gas adsorption/storage [38,39].

Various carbonaceous materials such as anthracite [40],

pitch [41], natural raw materials [42–47], synthetic organic

polymers [34,48], and various structured carbons [49–51] have

been activated by KOH to form porous carbons with high sur-

face areas and pore volume. For example, Sevilla and co-

workers synthesized nitrogen-doped porous carbons with

surface area of up to 3480 m2/g by KOH activation of polypyr-

role as carbon source [34]. A H2 uptake of 2.63 wt% was

obtained at 1 bar and �196 �C for these carbons. They also

reported the similar H2 uptake (2.6–2.7 wt%) was obtained

for zeolite-templated porous carbons and zirconium carbide

derived carbons after chemical activation [51,52]. Wang and

co-workers recently adopted a two-step procedure in which

physical activation (with CO2) was followed by a chemical

KOH activation step. This doubly activated carbon with sur-

face area of up to 3190 m2/g exhibits a hydrogen uptake of

2.5 wt% at 1 bar and �196 �C [49]. However, from the view of

sustainability, environmental friendliness, and continuous

availability, biomass-based materials are more promising car-

bon sources for porous carbons [42–47,53,54]. Fungi are spread

worldwide as a food starting material. However their poten-

tial applications in material science have attracted little

attention so far [55,56].

In this paper, we show the simple preparation of porous

carbons with high surface areas using various fungi as carbon

sources by KOH activation. Fungi are selected as carbon

sources because they can grow fast and thus be available in

abundance. So, large amount of porous carbons with homoge-

neous compositions can be expectedly prepared from these

fungi. Four kind of fungi (Auriculariales, Coprinus comatus,

Lentitus edodes, and Agaricus) used in present research are

normally available from a commercial source. By adjusting

the activation parameters (temperature and KOH amount),

the textural properties of final porous carbons are accordingly

controlled. The hydrogen uptakes of these resulting porous

carbons at �196 �C were investigated at ambient pressure

(1 bar) and high pressure (up to 75 bars), respectively.

2. Experimental section

2.1. Preparation of fungi-based activated carbons

Various fungi used in present research were bought from a

commercial source. Auriculariales (AU) and lentitus edodes

(LE) were obtained in the form of dry goods, while Coprinus

comatus (CO) and Agaricus (AG) were fresh. Before use, dry

fungi were immersed in warm water overnight to swell them.

All these fungi were washed with deionized water to remove

the impurities, cut into small pieces, and then dried at 80 �C.

These clean, dry fungi samples were pre-carbonized at 500 �Cwith 2 �C/min for 2 h in Ar. The resulting fungi-based chars

(AU-char, LE-char, CO-char, and AG-char) were ground into

powder before further activation. Chemical activation of the

fungi-based chars by KOH was performed in the temperature

range of 600–750 �C with KOH/char weight ratios of 1/1, 2/1,

4/1, or 5/1. In a typical activation process, the carbonized

fungi char was thoroughly mixed with KOH pellets using a

mortar with a pestle and then the mixture was put into a

ceramic crucible. The mixture was heated to the desired tem-

perature for 1 h with 3 �C/min under an argon gas flow. The

activated sample was then thoroughly washed several times

with HCl (10% by weight) to remove any inorganic salts, large

amount of distilled water until neutral pH, and finally dried at

120 �C in an oven. The resulting activated carbons were

named as X–Y–T, X is the fungus designation, Y is the weight

ratio of KOH/carbon (i.e., 1, 2, 4, or 5), and T is the activation

temperature (600–750) in �C.

2.2. Characterization

X-ray powder diffraction (XRD) patterns were recorded in

transmission geometry using a Stoe Stadi-P diffractometer

and Cu Ka1 radiation (k = 0.15406 nm). Nitrogen adsorption

isotherms were collected at �196 �C using a Quantachrome

Autosorb 1C apparatus. Prior to the measurement, the sam-

ples were degassed in vacuum at 150 �C for 16 h. Specific sur-

face areas were calculated using the Brunauer–Emmett–Teller

(BET) equation (p/p0 = 0.05–0.15) [57]. The total pore volume

was determined at relative pressure p/p0 = 0.98. The pore size

distribution was estimated according to the quenched solid

density functional theory (QSDFT) equilibrium model for slit

pores using the Autosorb 1.56 software from Quantachrome.

The micropore volume and surface area were also calculated

using the above mentioned DFT model. 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 BSE (backscattered electron) detector from Zeiss. The

packing density of the resulting porous carbons was

measured by pressing carbon (�0.5 g) in a mold at a pressure

of 550 kg/cm2.

2.3. Hydrogen uptake measurements

Before measurements, the sample was degassed at 150 �C in

vacuum overnight. Hydrogen physisorption isotherms at

�196 �C up to 1 bar were collected using a Quantachrome

Autosorb 1C apparatus.

High pressure hydrogen uptake measurements were

performed at �196 �C up to 75 bar. A high pressure volumetric

BELSORP-HP apparatus was used to quantify the Gibbs excess

amount of hydrogen adsorbed. Assuming that helium is

not adsorbed at 25 �C, the sample volume and so called

helium density of the sample were determined by helium

measurement.

C A R B O N 7 5 ( 2 0 1 4 ) 3 7 2 – 3 8 0 373

Author's personal copy

3. Results and discussion

As shown in Fig. 1, the fungi-based porous carbons in the

present study were synthesized from four kinds of different

fungi purchased from a commercial source. The as-received

fungi were transformed into porous carbons using a two-step

procedure: pre-carbonization at 500 �C of clean, dry fungi; and

chemical activation of the resulting chars with KOH. The evi-

dent morphological changes of the fungi-based chars sub-

jected to the chemical activation were observed by SEM.

SEM images (ESI 1) show that all calcinated chars are com-

posed of large irregular shaped particles. The morphologies

of these particles are different possibly due to their respective

unique textures of these fungi.

After the activation with KOH, all resulting porous carbons,

demonstrating a similar morphology, are composed of large

particles characterized by large cavities with pore sizes of

about 1–10 lm (ESI 2 a-b) and these pores have a smooth sur-

face, regardless of the char precursors. The morphology of

the activated porous carbon particles does not depend on

the char precursors derived from different fungi. This observa-

tion implies that the activated porous carbon nanoparticles

cannot maintain the structural morphology of their parent

chars. The formation of the cavities results from the gas

bubble production during the activation at high temperatures.

It is seen that porous carbon prepared at 750 �C has larger

cavities than that prepared at 600 �C, showing that more

carbon was burned off during the activation process at higher

activation temperature. The carbon combustion during the

activation process happens as a stoichoimetric solid–solid/

solid–liquid reaction [58], according to equation 6KOH + 2C!2 K + 3H2 + 2K2CO3. With further increasing activation temper-

ature to over 700 �C, the resulting K2CO3 starts to decompose

into K2O and CO2. Thus the high microporosity in the carbon

matrix is formed due to the ternary collaborative effects of

the chemical activation, the physical activation, and the

expansion of the carbon lattices by metallic potassium

intercalation. The yields of the resulting carbons varied from

�5% to 35% depending on the activation temperature and

KOH amount with respect to the char precursors. The TEM

images of the activated carbon AG-4-650 prepared using the

AG-char with 4/1 weight mass ratio of KOH/char at 650 �C evi-

dently shows the existence of large amounts of disordered

graphene layers forming the randomly oriented uniform

micropores (ESI 2c-d). Thus the obtained activated porous car-

bons have very large microporosity, large surface areas, and

uniform micropore sizes. Moreover, the XRD results indicate

a very low degree of graphitic structure in these fungi-based

porous carbons (ESI 3), which match well with those obtained

by TEM analysis.

The porosity of the fungi-based chars and activated porous

carbons was investigated by N2 adsorption measurements at

�196 �C, as presented in Figs. 2–4, and the textural properties

are summarized in Table 1. The fungi-based char has hardly

any porosity and show surface area of lower than 5 m2/g

(Fig. 2). The surface area value is well in consistence with the

external surface area determined by the as-plot technique.

Thus their surface areas of these chars are derived from

inter-particle voids, and there are no any framework-confined

pores. Notably, after the chemical activation with KOH, all the

char materials form highly porous carbons with the BET sur-

face areas typically >1600 m2/g, pore volume >0.8 cm3/g, and

narrow pore size distributions. A high porosity is ascribed to

large amount of uniform micropores in these activated

carbons.

The porosity of porous carbons prepared by the chemical

activation is highly related to both, the activation tempera-

ture and KOH amount used. Thus, we further investigated

the effects of these two parameters on the microstructures

of porous carbons on the example of AG-based char. Fig. 2

shows N2 adsorption isotherms and pore size distributions

of the resulting porous carbons prepared by the chemical

activation of AG-based char at 700 �C for 1 h using different

KOH/char ratios (1/1–5/1). With increasing the KOH amounts

used, the knees of the isotherms evidently changes widening,

showing the broadening of micropores and the formation of

Auriculariales

Lentinus edodes

Coprinus comatus

Agaricus

Fig. 1 – Transformation of various fungi into highly porous carbon materials by a pre-carbonization process followed by

chemical activation by KOH. (left) Photographs of four kinds of different fungi; (right) photograph and SEM image of the fungi-

based porous carbon. (A color version of this figure can be viewed online.)

374 C A R B O N 7 5 ( 2 0 1 4 ) 3 7 2 – 3 8 0

Author's personal copy

larger micropores. The micropore widening could be con-

firmed by the DFT pore size distributions as shown in

Fig. 2b. It is evident that the micropore sizes become broader

as the increase of KOH/char ratio. The samples obtained at

KOH/char ratio of 1/1 and 2/1 possess only pore size systems

centered at �0.8 nm, but the latter has little wider pore size.

The samples activated using KOH/char ratio of 4/1 and 5/1

not only demonstrate a gradual broadening of pore size distri-

butions, but also have a second pore system at 1.43 nm for the

former and 1.86 nm for the latter. The latter is also much big-

ger than the former. These data imply the larger pore sizes of

the activated porous carbons as the increase of KOH amounts.

However, as shown in Table 1, the surface areas of these car-

bons increase with increasing KOH/char ratios only up to 4/1

ratio. A further increase in KOH/char ratio to 5/1 results in a

reduction in surface area because of the over-activation and

thus a hysteresis is observed at p/p0 = 0.4–0.6 due to pore wid-

ening. These results reveal that the optimal KOH/char ratio

for activating the fungi-based char is 4/1, which is well in con-

sistence with those previously reported for anthracite-based

materials [59].

After confirming an optimized KOH/char ratio of 4/1, we

also studied the influences of different activation tempera-

tures between 600 and 750 �C on the porosity of the activated

carbons. The nitrogen sorption isotherms and the corre-

sponding pore size distributions are shown in Fig. 3. The

shape of the isotherm changes significantly with the increase

of the activation temperature, indicating the high impact of

activation temperature on the porosity of the activated car-

bons. The isotherms of the samples activated below 700 �Cexhibit a rounded knee in relative pressure (P/P0) region of

0.1–0.3, demonstrating the presence of (large) micropores in

these carbons. For the sample activated at higher tempera-

ture (750 �C), the knee of the isotherm shifts to higher relative

pressure (0.3–0.5) and a hysteresis is found, showing the exis-

tence of a second pore system in the mesopore size rage and a

large content of mesoporosity. Indeed, the pore size distribu-

tions curves indicate that the samples obtained at low activa-

tion temperatures (600–700 �C) have a well-defined micropore

system (0.83 nm) as well as a small proportion of a little bigger

micropore (1.3–1.4 nm), while the sample activated at 750 �Chas a sharp peak for a mesopore system centered at about

2.05 nm. These textural data reveal that the pore widening

and the formation of new mesopores at higher activation

temperatures are correlated to the gasification of the char

by CO2 formed during K2CO3 decomposition [15]. All these

carbon get higher surface areas and pore volumes with

increasing activation temperature (Table 1). Moreover with

higher activation temperature used, the yield of porous car-

bons is lower, implying that more carbon was burned off dur-

ing the activation. However, sample activated at 750 �Cevidently has large portion of mesopores being less efficient

for H2 adsorption at low pressure [60–62].

0.0 0.2 0.4 0.6 0.8 1.0

0

100

200

300

400

500

600

700

11 0

AG-1-700 AG-2-700 AG-4-700 AG-5-700 AG-char

(b)

AG-1-700 AG-2-700 AG-4-700 AG-5-700 AG-char

Volu

me

adso

rbed

(cm

3 /g S

TP)

Relative pressure (P/P0)

(a)

Pore size (nm)

increasing themass ratioof KOH/char

Fig. 2 – Nitrogen adsorption isotherms (a) and pore size

distributions (b) of AG-char and activated carbons derived

from AG-char activated at 700 �C using variable KOH/char

ratios (1, 2, 4, and 5). (A color version of this figure can be

viewed online.)

0.0 0.2 0.4 0.6 0.8 1.0200

300

400

500

600

700

800

900

1000

1 10

(b)

AG-4-600 AG-4-650 AG-4-700 AG-4-750

Volu

me

adso

rbed

(cm

3 /g S

TP)

Relative pressure (P/P0)

(a) AG-4-600 AG-4-650 AG-4-700 AG-4-750

Pore size (nm)

Fig. 3 – Nitrogen adsorption isotherms (a) and pore size

distributions (b) of activated carbons prepared using AG-

char as precursor with KOH/char = 4 at different

temperatures (600, 650, 700, and 750 �C). (A color version of

this figure can be viewed online.)

0.0 0.2 0.4 0.6 0.8 1.0

0

100

200

300

400

500

600

700

1 2 3 4 5

AU-4-700 CO-4-700 LE-4-700 AG-4-700

(b)

AU-4-700 CO-4-700 LE-4-700 AG-4-700Vo

lum

e ad

sorb

ed (c

m3 /g

STP

)

Relative pressure (P/P0)

(a)

Pore size (nm)

Fig. 4 – Nitrogen adsorption isotherms (a) and pore size

distributions (b) of activated fungi-based carbons prepared

with KOH/char = 4 at 700 �C. (A color version of this figure

can be viewed online.)

C A R B O N 7 5 ( 2 0 1 4 ) 3 7 2 – 3 8 0 375

Author's personal copy

We have studied the activation parameters (temperature

and KOH amount) on the porosity of the activated carbons.

It was found that the sample activated at 700 �C for 1 h and

a KOH/char ratio of 4/1 has relatively high surface area and

pore volume in the micropore range, an advantage for

enhanced gas adsorption. Subsequently, we further investi-

gated the effects of different fungi-based char precursors on

the porosity of the activated carbons using this optimized

parameters. As shown in Fig. 4, the shapes of the isotherms

and pore size distributions for porous carbons are very simi-

lar, indicating very low impact of the char precursors on the

porosity and pore microstructure of the final activated car-

bons. All these adsorption isotherms are type I, typical for

microporous materials. The surface areas and the total pore

volumes of these porous carbons ranging from 1983 to

2264 m2/g, and 0.90–1.02 cm3/g, respectively, are independent

of the char precursors. Moreover the DFT pore size distribu-

tions indicate that these carbons have similar narrow microp-

ores with the size of about 0.83 nm. The existence of uniform

micropores lower than 1 nm in porous carbons is beneficial

for efficient gas adsorption.

The potential of the fungi-based activated carbons as

hydrogen adsorption materials was investigated at �196 �C.

Fig. 5 demonstrates the H2 adsorption isotherms for various

carbons at �196 �C up to 1 bar. H2 uptake capacities and H2

density for various activated carbons are summarized in

Table 2. The porous carbons, prepared under the optimized

conditions using different chars as the precursors, show sim-

ilar H2 uptake capacity of 2.2–2.4 wt% at 1 bar and �196 �C,

because these porous carbons possess similar surface areas

and pore volumes. This result implies that the intrinsic tex-

tures of the biomass precursors cannot affect the microporos-

ity of the final porous carbons, further having an effect on the

H2 uptakes. Hydrogen uptake of porous materials at low pres-

sure is usually dominated by pores in the sub-nanometer

range. Several researchers have reported that the optimum

pore size for H2 adsorption is 0.7 nm [31–34]. Moreover, AG-

4–700 has an H2 uptake of 2.4 wt% at 1 bar and �196 �C,

whereas both, the increase and decrease in the activation

temperature result in lower H2 adsorption capacities (2.0–

2.1 wt%). This is because AG-4–650 and AG-750 have evidently

lower pore volumes (0.131–0.171 cm3/g) for the pore

size < 0.72 nm than AG-4–700 (0.222 cm3/g). Thus, our findings

are consistent with previous studies [34,46].

The results of our present study demonstrate that the

fungi-based activated carbons show good H2 adsorption

capacities of 2.4 wt% at 1 bar and �196 �C compared to those

previously reported. The comparison is illustrated in Fig. 6,

where the amount of hydrogen adsorbed at 77 K and 1 bar is

plotted over the BET surface area. Although under these con-

ditions hydrogen adsorption is controlled by the volume of

narrow micropores <0.7 nm [31–34], which can be efficiently

calculated by applying the Dubinin–Radushkevic (DR) method

according to CO2 adsorption isotherms obtained at 0 �C and

sub-atmospheric pressures, these values are not always

reported in the literature. For this reason the BET surface area

was used in Fig. 6, even though the DR micropore volume from

CO2 data may result in a better correlation. It is clear that the

present carbons have similar or good H2 uptake capacities

compared to previously reported carbonaceous materials

which adsorb no more than 2.8 wt% H2 under the same condi-

tions. For example, the commercially available AX21 adsorbs

2.4 wt% of H2 at �196 �C and 1 bar [25]. At �196 �C and 1 bar,

the activated carbons from mesophase pitch demonstrated a

H2 adsorption capacity of 2.8 wt% [41]. Various natural raw

Table 1 – Textural properties of activated fungi-based carbons.

Sample Textural properties

SBETa (m2/g) Vp

b (cm3/g) Smicroc (m2/g) Vmicro

c (cm3/g) Dpored (nm)

AG-1–700 1600 0.72 1551 0.66 0.83AG-2–700 1742 0.80 1581 0.82 0.83AG-4–700 2264 1.02 1970 0.92 0.83, 1.43AG-5–700 1778 1.02 1217 0.67 0.91, 1.86AG-4–600 1783 0.82 1532 0.72 0.83, 1.34AG-4–650 2188 1.04 1705 0.88 0.83, 1.34AG-4–750 2526 1.56 1563 0.91 0.89, 2.05AU-4–700 2137 0.95 1930 0.87 0.83CO-4–700 2159 0.98 1771 0.87 0.83LE-4–700 1983 0.90 1700 0.81 0.83, 1.43a Specific surface area determined by the BET equation (p/p0 = 0.05–0.15).b Total pore volume at p/p0 = 0.98.c Micropore volume and micropore surface area estimated d < 2 nm by the QSDFT method using equilibrium model for slit pores.d Maxima of the pore size distribution calculated by the QSDFT method.

0.0 0.2 0.4 0.6 0.8 1.00.0

0.5

1.0

1.5

2.0

2.5

H2 u

ptak

e (w

t%)

Pressure (bar)

AU-4-700 AG-4-700 AG-4-750 AG-4-650 LE-4-700

Fig. 5 – The H2 uptake isotherms for various fungi-based

porous carbons at �196 �C up to 1 bar. (A color version of

this figure can be viewed online.)

376 C A R B O N 7 5 ( 2 0 1 4 ) 3 7 2 – 3 8 0

Author's personal copy

materials and the derivatives were transformed into the acti-

vated carbons by pre-treatment, followed by KOH activation

[42–47,63–65] and the highest H2 uptakes reported were

2.0 wt%, 2.6 wt%, and 2.7 wt% for corncob- [42], wood- [43],

and Quercus agrifolia-based activated carbons [45], respectively,

at �196 �C and 1 bar. Adsorption of H2 at 0.93 bar showed the

H2 uptake (2.5 wt%) for the sucrose based activated with sur-

face area of 1825 m2/g [65]. Activated ZrC-CDC could adsorb

2.7 wt% of H2 at 1 bar and �196 �C. More recently, Jiang and

his co-workers reported a MOF-based carbon with an unex-

pectedly high surface area (3405 m2/g) and H2 uptake capacity

of 2.77 wt% at 1 bar and �196 �C [66], which is a little higher

than our values. The polymer blend CNFs activated by alkaline

hydroxides could adsorb 2.38 wt% H2 at 1 bar and �196 �C,

similar to our values [67]. Xia et al. synthesized various

ordered porous carbons templated from zeolites, which only

adsorbed 2.16 wt% H2 at 1 bar and�196 �C [68]. The H2 adsorp-

tion capacities of these fungi-based porous carbons evidently

exceed the activated multi-walled carbon nanotube-graphite

mixture (H2 uptake: 0.34–0.75 wt% at 1 bar and �196 �C) [69].

Although the fungi-based activated carbon does not outper-

form porous carbon yielded by the direct pyrolysis of zinc-con-

taining MOFs (H2 uptake: 3.25 wt%) [26], Ti-CDC (H2 uptake:

3.0 wt%) [61] and nitrogen-doped porous polymers (H2 uptake:

3.05 wt%) [70] at 1 bar and �196 �C, from the view of social

sustainability, fungi-based porous carbons derived from

renewable natural abundant biomass are more promising for

H2 on-board storage.

The hydrogen uptake capacities of various fungi-based

activated carbons were also investigated at high pressure

and �196 �C. The H2 adsorption isotherms are presented in

Fig. 7 and the H2 uptake values are collected in Table 2. The

H2 adsorption density for the samples based on one gram

0 20 40 60 80

AG-4-700 AU-4-700 CO-4-700 LE-4-700

5

4

2

3

0

H2 u

ptak

e (w

t%)

Pressure (bar)

1

Fig. 7 – The high pressure (up to 75 bar) H2 adsorption

isotherms at �196 �C for a set of activated carbons prepared

at the activation temperature of 700 �C and a KOH/char mass

ratio of 4/1 using different fungi as the precursors. (A color

version of this figure can be viewed online.)

0 1000 2000 3000 40000.0

0.5

1.0

1.5

2.0

2.5

3.0

anthracite pitch natural biomass synthetic organic polymer template porous carbon ZrC-CDC carbon nanofibers MOF-based carbon multwalled CNTs composite fungi (present work)

H2 u

ptak

e (w

t%)

Specific surface area (m2/g)

Fig. 6 – A comparison of H2 uptake capacity at �196 �C and 0.93–1.1 bar vs. specific surface areas for various KOH-activated

carbons derived from and various fungi (present work) and anthracite [40], pitch [41], natural raw materials [42,43,45–47,65],

synthetic organic polymers [34,48], and various structured carbons (template porous carbons [50,51], ZrC-CDC [52], carbon

nanofibers [40,67], MOF-based carbon [66], and multi-walled CNTs-graphite composite [40,69]). (A color version of this figure

can be viewed online.)

Table 2 – The hydrogen uptake capacities of activated fungi-based carbons at �196 �C.

Sample H2 uptake at1 bar (wt%)

Maximum excess H2

uptake (wt%)H2 adsorption densityat 1 bar (lmol H2 m�2)

Maximum H2 adsorptiondensity (lmol H2 m�2)

AU-4–700 2.3 4.5 5.5 10.5CO-4–700 – 4.2 – 9.7LE-4–700 2.2 4.2 5.7 10.6AG-4–700 2.4 4.7 5.4 10.4AG-4–650 2.0 – 4.7 –AG-4–750 2.1 – 4.3 –

C A R B O N 7 5 ( 2 0 1 4 ) 3 7 2 – 3 8 0 377

Author's personal copy

adsorbent is also calculated using the equation: H2 adsorption

density = mole (H2 amount adsorbed)/surface area (m2). The

adsorption/desorption of H2 in these porous carbons is totally

reversible. The maximum Gibbs excess amounts adsorbed for

four fungi-based porous carbons vary between 4.2 and

4.7 wt% at pressures of ca. 35–40 bar. Among these fungi-

based carbons, AG-4–700 has the highest H2 uptake

(4.7 wt%) because of the high surface area and pore volume.

Notably it has similar H2 adsorption density (10.4 lmol

H2 m�2) as other fungi-based porous carbons. The packing

density of AG-4-700 is measured to be 0.49 g/cm3, and thus

the corresponding hydrogen adsorption capacity of 24.2 g/L

is obtained on volumetric basis. It was reported that the rela-

tively big micropores in porous carbons only contribute to a

minor extent to H2 adsorption at ambient pressures, but they

are efficient at high pressures [33,34]. In comparison with our

values with those reported in the literatures, the fungi-based

porous carbons match well with the results from other porous

carbon adsorbents. For example, the maximum adsorption

hydrogen capacity of about 5.0 wt% was obtained at 77 K

and high pressure [71]. Various porous carbons prepared by

the activation of anthracite demonstrated high hydrogen

uptake capacities of 5.3–6.0 wt% at 77 K and high pressure,

which are better than fungi-based porous carbons [40,72,73].

Roth and co-workers found the best material with specific

surface area of 2560 m2/g among various carbon nanostruc-

tures shows the similar uptake capacity of 4.5 wt% at 77 K

as ours (4.2–4.7 wt%) [74]. The H2 uptake for fungi-based acti-

vated carbons is also comparable to those (4.4–5.2 wt%)

obtained from various mesoporous carbide derived carbons

with very high surface areas (2500–3000 m2/g) under similar

conditions [14,75], but they are higher than that of micropo-

rous carbide derived carbons (3.9 wt%) [75], MCM-48-

templated mesoporous carbon (2.7 wt% at 60 bar and

�196 �C) [76], and SBA-15-templated mesoporous carbon

(2.9 wt% at 30 bar and �196 �C) [75]. Thus the fungi-based

activated carbons derived from sustainable, easily available

biomass demonstrate a great potential in H2 adsorption.

4. Conclusions

In conclusion, we reported the successful synthesis of a set of

porous carbons using different fungi as the precursors. The

porosities of the resulting porous carbons strongly depend

on the activation parameters (temperature and KOH amount),

whereas the kind of fungi used as precursor has less impact.

The surface areas and pore volumes of the resulting porous

carbons are in the region of 1600–2500 m2/g, and 0.80–

1.56 cm3/g, respectively. All resulting porous carbons have a

uniform micropore with size of 0.8–0.9 nm, but some have

another set of micropores (1.3–1.4 nm) which are further

broadened to 1.9–2.1 nm with the increase of either the acti-

vation temperature to 750 �C or KOH/char mass ratio to 5/1.

Due to similar textural properties (surface areas and

micropore sizes) of these fungi-based porous carbons pre-

pared under the optimized synthesis conditions, the porous

carbons have similar H2 uptake of 2.2–2.4 wt% at 1 bar and

�196 �C. At high pressure, the excess hydrogen uptake in

the range 4.2–4.7 wt% was obtained and �196 �C. These

uptakes of fungi-based activated carbons are comparable or

higher than those obtained for ordered mesoporous CDC

powders, microporous CDC powders, and mesoporous silica

templated porous carbons, implying a great potential of

fungi-based porous carbons as H2 adsorption media.

Acknowledgements

J. W. thanks Shanghai Institute of Ceramics, the One Hundred

Talent Plan of Chinese Academy of Sciences, and National

Natural Science Foundation of China, China (Grant No.

21307145) for the financial support. This work was partly sup-

ported by the Alexander von Humboldt Foundation, Germany.

Appendix A. Supplementary data

Supplementary data associated with this article can be found,

in the online version, at http://dx.doi.org/10.1016/j.carbon.

2014.04.016.

R E F E R E N C E S

[1] Ryoo R, Joo SH, Kruk M, Jaroniec M. Ordered mesoporouscarbons. Adv Mater 2001;13(9):677–81.

[2] Novoselov KS, Geim AK, Morozov SV, Jiang D, Zhang Y,Dubonos SV, et al. Electric field effect in atomically thincarbon films. Science 2004;306(5696):666–9.

[3] Arico AS, Bruce P, Scrosati B, Tarascon J-M, Van Schalkwijk W.Nanostructured materials for advanced energy conversionand storage devices. Nature Mater 2005;4(5):366–77.

[4] Aziz AA, Bakar SA, Rusop M. Carbon nanostructuredmaterials. Carbon and oxide nanostructures. Springer; 2011.p. 165–93.

[5] Sevilla M, Fuertes AB. Sustainable porous carbons with asuperior performance for CO2 capture. Energy Environ Sci2011;4(5):1765–71.

[6] Wang R, Wang P, Yan X, Lang J, Peng C, Xue Q. Promisingporous carbon derived from celtuce leaves with outstandingsupercapacitance and CO2 capture performance. ACS ApplMater Interfaces 2012;4(11):5800–6.

[7] Wang JC, Senkovska I, Oschatz M, Lohe MR, Borchardt L,Heerwig A, et al. Imine-linked polymer derived nitrogen-doped microporous carbons with excellent CO2 captureproperties. ACS Appl Mater Interfaces 2013;5:3160–7.

[8] Wang JC, Senkovska I, Oschatz M, Lohe MR, Borchardt L,Heerwig A, et al. Highly porous nitrogen-doped polyimine-based carbons with adjustable microstructures for CO2

capture. J Mater Chem A 2013;1:10951–61.[9] Wang J, Liu Q. An efficient one-step condensation and

activation strategy to synthesize porous carbons withoptimal micropore sizes for highly selective CO2 adsorption.Nanoscale 2014;6(8):4148–56.

[10] Dreyer DR, Bielawski CW. Carbocatalysis: heterogeneouscarbons finding utility in synthetic chemistry. Chem Sci2011;2(7):1233–40.

[11] Yu J-S, Kang S, Yoon SB, Chai G. Fabrication of ordereduniform porous carbon networks and their application to acatalyst supporter. J Am Chem Soc 2002;124(32):9382–3.

[12] Krawiec P, Kockrick E, Borchardt L, Geiger D, Corma A, KaskelS. Ordered mesoporous carbide derived carbons: novelmaterials for catalysis and adsorption. J Phys Chem C2009;113(18):7755–61.

378 C A R B O N 7 5 ( 2 0 1 4 ) 3 7 2 – 3 8 0

Author's personal copy

[13] Oschatz M, Borchardt L, Thommes M, Cychosz KA,Senkovska I, Klein N, et al. Carbide-derived carbonmonoliths with hierarchical pore architectures. AngewChem-Int Edit 2012;51(30):7577–80.

[14] Wang JC, Oschatz M, Biemelt T, Borchardt L, Senkovska I,Lohe MR, et al. Synthesis, characterization, and hydrogenstorage capacities of hierarchical porous carbide derivedcarbon monolith. J Mater Chem 2012;22(45):23893–9.

[15] Wang JC, Kaskel S. KOH activation of carbon-based materialsfor energy storage. J Mater Chem 2012;22(45):23710–25.

[16] Zhu Y, Murali S, Stoller MD, Ganesh KJ, Cai W, Ferreira PJ,et al. Carbon-based supercapacitors produced by activationof graphene. Science 2011;332(6037):1537–41.

[17] Latorre-Sanchez M, Primo A, Garcia H. Green synthesis ofFe3O4 nanoparticles embedded in a porous carbon matrixand its use as anode material in Li-ion batteries. J MaterChem 2012;22(40):21373–5.

[18] Wang JC, Yu XF, Li YX, Liu Q. Poly(3,4-ethylenedioxythiophene)/mesoporous carbon composite. JPhys Chem C 2007;111(49):18073–7.

[19] Porada S, Weinstein L, Dash R, Van Der Wal A, Bryjak M,Gogotsi Y, et al. Water desalination using capacitivedeionization with microporous carbon electrodes. ACS ApplMater Interfaces 2012;4(3):1194–9.

[20] Otowa T, Nojima Y, Miyazaki T. Development of KOHactivated high surface area carbon and its application todrinking water purification. Carbon 1997;35(9):1315–9.

[21] Wang JC, Xiang CS, Liu Q, Pan YB, Guo JK. Orderedmesoporous carbon/fused silica composites. Adv FunctMater 2008;18(19):2995–3002.

[22] Zhou H, Wang J, Zhuang J, Liu Q. A covalent route for efficientsurface modification of ordered mesoporous carbon as highperformance microwave absorbers. Nanoscale2013;5(24):12502–11.

[23] Zhou H, Wang J, Zhuang J, Liu Q. Synthesis andelectromagnetic interference shielding effectiveness ofordered mesoporous carbon filled poly (methyl methacrylate)composite films. RSC Adv 2013;3:23715–21.

[24] Wang J, Zhou H, Zhuang J, Liu Q. Influence of spatialconfigurations on electromagnetic interference shielding ofordered mesoporous carbon/ordered mesoporous silica/silicacomposites. Sci Rep 2013;3:3252.

[25] Texier-Mandoki N, Dentzer J, Piquero T, Saadallah S, David P,Vix-Guterl C. Hydrogen storage in activated carbon materials:role of the nanoporous texture. Carbon 2004;42(12):2744–7.

[26] Yang SJ, Kim T, Im JH, Kim YS, Lee K, Jung H, et al. MOF-derived hierarchically porous carbon with exceptionalporosity and hydrogen storage capacity. Chem Mater2012;24(3):464–70.

[27] Turner JA. Sustainable hydrogen production. Science2004;305(5686):972–4.

[28] Dunn S, Peterson JA. Hydrogen futures: toward a sustainableenergy system. Washington, DC: Worldwatch Institute;2001.

[29] Schlapbach L, Zuttel A. Hydrogen-storage materials formobile applications. Nature 2001;414(6861):353–8.

[30] Sakintuna B, Lamari-Darkrim F, Hirscher M. Metal hydridematerials for solid hydrogen storage: a review. Int J HydrogenEnergy 2007;32(9):1121–40.

[31] Rzepka M, Lamp P, De la Casa-Lillo M. Physisorption ofhydrogen on microporous carbon and carbon nanotubes. JPhys Chem B 1998;102(52):10894–8.

[32] Georgiev P, Ross D, Albers P, Ramirez-Cuesta A. The rotationaland translational dynamics of molecular hydrogenphysisorbed in activated carbon: a direct probe ofmicroporosity and hydrogen storage performance. Carbon2006;44(13):2724–38.

[33] Gogotsi Y, Portet C, Osswald S, Simmons JM, Yildirim T,Laudisio G, et al. Importance of pore size in high-pressurehydrogen storage by porous carbons. Int J Hydrogen Energy2009;34(15):6314–9.

[34] Sevilla M, Mokaya R, Fuertes AB. Ultrahigh surface areapolypyrrole-based carbons with superior performance forhydrogen storage. Energy Environ Sci 2011;4(8):2930–6.

[35] Lee J, Kim J, Hyeon T. Recent progress in the synthesis ofporous carbon materials. Adv Mater 2006;18(16):2073–94.

[36] Marsh H, Reinoso FR. Activatedcarbon. Amsterdam: Elsevier; 2006.

[37] Otowa T, Tanibata R, Itoh M. Production and adsorptioncharacteristics of MAXSORB: high-surface-area activecarbon. Gas Sep Purif 1993;7(4):241–5.

[38] Gogotsi Y, Dash RK, Yushin G, Yildirim T, Laudisio G, FischerJE. Tailoring of nanoscale porosity in carbide-derived carbonsfor hydrogen storage. J Am Chem Soc 2005;127(46):16006–7.

[39] Presser V, McDonough J, Yeon S-H, Gogotsi Y. Effect of poresize on carbon dioxide sorption by carbide derived carbon.Energy Environ Sci 2011;4(8):3059–66.

[40] Jorda-Beneyto M, Suarez-Garcia F, Lozano-Castello D,Cazorla-Amoros D, Linares-Solano A. Hydrogen storage onchemically activated carbons and carbon nanomaterials athigh pressures. Carbon 2007;45(2):293–303.

[41] Monteiro de Castro M, Martinez-Escandell M, Molina-SabioM, Rodriguez-Reinoso F. Hydrogen adsorption on KOHactivated carbons from mesophase pitch containing Si, B, Tior Fe. Carbon 2010;48(3):636–44.

[42] Sun Y, Webley PA. Preparation of activated carbons fromcorncob with large specific surface area by a variety ofchemical activators and their application in gas storage.Chem Eng J 2010;162(3):883–92.

[43] Huang C-C, Chen H-M, Chen C-H, Huang J-C. Effect of surfaceoxides on hydrogen storage of activated carbon. Sep PurifTechnol 2010;70(3):291–5.

[44] Im JS, Kwon O, Kim YH, Park S-J, Lee Y-S. The effect ofembedded vanadium catalyst on activated electrospun CFsfor hydrogen storage. Microporous Mesoporous Mater2008;115(3):514–21.

[45] Figueroa-Torres MZ, Robau-Sanchez A, De la Torre-Saenz L,Aguilar-Elguezabal A. Hydrogen adsorption bynanostructured carbons synthesized by chemical activation –low pressure. Microporous Mesoporous Mater 2007;98(1–3):89–93.

[46] Sevilla M, Fuertes AB, Mokaya R. High density hydrogenstorage in superactivated carbons from hydrothermallycarbonized renewable organic materials. Energy Environ Sci2011;4(4):1400–10.

[47] Guo H, Gao Q. Cryogenic hydrogen uptake of high surfacearea porous carbon materials activated by potassiumhydroxide. Int J Hydrogen Energy 2010;35(14):7547–54.

[48] Sevilla M, Fuertes AB, Mokaya R. Preparation and hydrogenstorage capacity of highly porous activated carbon materialsderived from polythiophene. Int J Hydrogen Energy2011;36(24):15658–63.

[49] Wang H, Gao Q, Hu J. High hydrogen storage capacity ofporous carbons prepared by using activated carbon. J AmChem Soc 2009;131(20):7016–22.

[50] Zheng Z, Gao Q, Jiang J. High hydrogen uptake capacity ofmesoporous nitrogen-doped carbons activated usingpotassium hydroxide. Carbon 2010;48(10):2968–73.

[51] Sevilla M, Alam N, Mokaya R. Enhancement of hydrogenstorage capacity of zeolite-templated carbons by chemicalactivation. J Phys Chem C 2010;114(25):11314–9.

[52] Sevilla M, Foulston R, Mokaya R. Superactivated carbide-derived carbons with high hydrogen storage capacity. EnergyEnviron Sci 2010;3(2):223–7.

C A R B O N 7 5 ( 2 0 1 4 ) 3 7 2 – 3 8 0 379

Author's personal copy

[53] Wei L, Sevilla M, Fuertes AB, Mokaya R, Yushin G.Hydrothermal carbonization of abundant renewable naturalorganic chemicals for high-performance supercapacitorelectrodes. Adv Energy Mater 2011;1(3):356–61.

[54] Hu B, Wang K, Wu L, Yu SH, Antonietti M, Titirici MM.Engineering carbon materials from the hydrothermalcarbonization process of biomass. Adv Mater2010;22(7):813–28.

[55] Wang JC, Heerwig A, Lohe MR, Oschatz M, Borchardt L, KaskelS. Fungi-based porous carbons for CO2 adsorption andseparation. J Mater Chem 2012;22(28):13911–3.

[56] Zhu H, Wang X, Yang F, Yang X. Promising carbons forsupercapacitors derived from fungi. Adv Mater2011;23(24):2745–8.

[57] Brunauer S, Emmett PH, Teller E. Adsorption of gases inmultimolecular layers. J Am Chem Soc 1938;60:309–19.

[58] Lozano-Castello D, Calo JM, Cazorla-Amoros D, Linares-Solano A. Carbon activation with KOH as explored bytemperature programmed techniques, and the effects ofhydrogen. Carbon 2007;45(13):2529–36.

[59] Lozano-Castello D, Lillo-Rodenas MA, Cazorla-Amoros D,Linares-Solano A. Preparation of activated carbons fromSpanish anthracite I. Activation by KOH. Carbon2001;39(5):741–9.

[60] Texier-Mandoki N, Dentzer J, Piquero T, Saadallah S, David P,Vix-Guterl C. Hydrogen storage in activated carbon materials:role of the nanoporous texture. Carbon 2004;42(12–13):2744–7.

[61] Yushin G, Dash R, Jagiello J, Fischer JE, Gogotsi Y. Carbide-derived carbons: effect of pore size on hydrogen uptake andheat of adsorption. Adv Funct Mater 2006;16(17):2288–93.

[62] Bhatia SK, Myers AL. Optimum conditions for adsorptivestorage. Langmuir 2006;22(4):1688–700.

[63] Akasaka H, Takahata T, Toda I, Ono H, Ohshio S, Himeno S,et al. Hydrogen storage ability of porous carbon materialfabricated from coffee bean wastes. Int J Hydrogen Energy2011;36(1):580–5.

[64] Armandi M, Bonelli B, Cho K, Ryoo R, Garrone E. Study ofhydrogen physisorption on nanoporous carbon materials ofdifferent origin. Int J Hydrogen Energy 2011;36(13):7937–43.

[65] Armandi M, Bonelli B, Geobaldo F, Garrone E. Nanoporouscarbon materials obtained by sucrose carbonization in thepresence of KOH. Microporous Mesoporous Mater2010;132(3):414–20.

[66] Jiang H-L, Liu B, Lan Y-Q, Kuratani K, Akita T, Shioyama H,et al. From metal–organic framework to nanoporous carbon:toward a very high surface area and hydrogen uptake. J AmChem Soc 2011;133(31):11854–7.

[67] Suarez-Garcia F, Vilaplana-Ortego E, Kunowsky M, KimuraM, Oya A, Linares-Solano A. Activation of polymer blendcarbon nanofibres by alkaline hydroxides and theirhydrogen storage performances. Int J Hydrogen Energy2009;34(22):9141–50.

[68] Xia Y, Yang Z, Gou X, Zhu Y. A simple method for theproduction of highly ordered porous carbon materials withincreased hydrogen uptake capacities. Int J Hydrogen Energy2013;38:5039–52.

[69] Kopac T, Erdogan FO. Temperature and alkaline hydroxidetreatment effects on hydrogen sorption characteristics ofmulti-walled carbon nanotube-graphite mixture. J Ind EngChem 2009;15(5):730–5.

[70] Wang XS, Ma S, Forster PM, Yuan D, Eckert J, Lopez JJ, et al.Enhancing H2 uptake by ‘‘close-packing’’ alignment of opencopper sites in metal-organic frameworks. Angew Chem-IntEdit 2008;47(38):7263–6.

[71] Kunowsky M, Marco-Lozar JP, Cazorla-Amoros D, Linares-Solano A. Scale-up activation of carbon fibres forhydrogen storage. Int J Hydrogen Energy2010;35(6):2393–402.

[72] Fierro V, Szczurek A, Zlotea C, Mareche JF, Izquierdo MT,Albiniak A, et al. Experimental evidence of an upper limit forhydrogen storage at 77 K on activated carbons. Carbon2010;48(7):1902–11.

[73] Fierro V, Zhao W, Izquierdo MT, Aylon E, Celzard A.Adsorption and compression contributions to hydrogenstorage in activated anthracites. Int J Hydrogen Energy2010;35(17):9038–45.

[74] Panella B, Hirscher M, Roth S. Hydrogen adsorption indifferent carbon nanostructures. Carbon 2005;43(10):2209–14.

[75] Kockrick E, Schrage C, Borchardt L, Klein N, Rose M,Senkovska I, et al. Ordered mesoporous carbide derivedcarbons for high pressure gas storage. Carbon2010;48(6):1707–17.

[76] Terres E, Panella B, Hayashi T, Kim YA, Endo M, DominguezJM, et al. Hydrogen storage in spherical nanoporous carbons.Chem Phys Lett 2005;403(4–6):363–6.

380 C A R B O N 7 5 ( 2 0 1 4 ) 3 7 2 – 3 8 0