Hydrogen storage capacity of highly porous carbons synthesized from biomass-derived aerogels
Hydrogen storage capacity of highly porous carbons synthesized from biomass-derived aerogels
Carbon letters. 2015. Apr, 16(2): 127-131
Copyright © 2015, Korean Carbon Society
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
  • Received : February 15, 2015
  • Accepted : March 24, 2015
  • Published : April 30, 2015
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About the Authors
Yong-Ki Choi
Soo-Jin Park

In this work, highly porous carbons were prepared by chemical activation of carbonized biomass-derived aerogels. These aerogels were synthesized from watermelon flesh using a hydrothermal reaction. After carbonization, chemical activation was conducted using potassium hydroxide to enhance the specific surface area and microporosity. The micro-structural properties and morphologies were measured by X-ray diffraction and scanning electron microscopy, respectively. The specific surface area and microporosity were investigated by N 2 /77 K adsorption-desorption isotherms using the Brunauer-Emmett-Teller method and Barrett-Joyner-Halenda equation, respectively. Hydrogen storage capacity was dependent on the activation temperature. The highest capacity of 2.7 wt% at 77 K and 1 bar was obtained with an activation temperature of 900℃.
1. Introduction
Hydrogen has many advantages as an alternative to fossil fuels, as it produces no pollutants, has high energy efficiency, and is essentially an unlimited resource [1 - 3] . However, its storage presents a problem. Many hydrogen storage methods have been extensively investigated, including metal hybrids, liquid hydrogen, high-pressure hydrogen, and adsorption [4 - 7] . Among these storage methods, adsorption by carbon materials has many advantages such as good heat resistance, chemical stability, reversibility, and low cost. Many carbon materials for adsorption have also been reported, and include activated carbon, carbon aerogels, graphene, and carbon nanotubes [8 - 12] .
Hydrogen storage capacity is strongly influenced by the specific surface area and microporosity of the adsorbents [13] . Therefore, various methods for the synthesis and surface modification of porous carbons have been developed; for example, templating with other porous materials such as zeolites, metal-organic frameworks (MOFs), and silica [14 - 17] , and direct carbonization of various precursors. Template methods are complicated because they involve the removal of the templated materials. Direct carbonization uses environmentally friendly precursors from agricultural wastes such as rice husks, corncobs, and coconut shells [18 , 19] . The use of these precursors is also helpful in preventing pollution caused by agricultural wastes. However, biomass-derived carbons (BCAs) have a relatively low specific surface area, and therefore they require activation to increase their specific surface area and micropore volume.
There are two activation methods that are used for BCAs: 1) chemical activation and 2) physical activation [20 , 21] . Chemical activation is conducted using acidic or basic chemicals such as H 3 PO 4 , KOH, Na 2 CO 3 , and NaOH and can lead to high specific surface area and microporosity as a consequence of erosion and oxidation. Physical activation requires an oxidizing gas, such as water vapor, carbon dioxide etc.
In this study, we prepared biomass-derived aerogels from watermelon flesh using a hydrothermal reaction, followed by carbonization. Chemical activation was conducted at various temperatures using KOH to enhance the hydrogen storage capacity of the aerogels.
2. Experimental
- 2.1. Materials and preparation
Biomass-derived aerogels were prepared by the hydrothermal reaction of watermelon flesh; the details have been provided elsewhere [22] . The watermelon flesh was cut and put into a 100-mL Teflon-lined autoclave. The hydrothermal reaction was conducted at 180℃ for 12 h, and then the sample was immersed in a mixture of distilled water and ethanol for several days to remove the impurities. After drying at 80℃ for 12 h, the obtained biomass-derived aerogels were carbonized under flowing N 2 (200 mL/min) at 550℃ for 1.5 h. The resulting BCA was mixed with KOH (mass ratio of 2), heated to a target temperature in the range 700℃-900℃ in a tubular furnace under N 2 atmosphere (200 mL/min), and maintained at the target temperature for 1 h. After cooling down to room temperature, the resulting materials were taken out and washed with distilled water and hydrochloric acid until the pH became neutral. The KOH-activated BCA was labeled K-T-BCA, where T denotes the activation temperature.
- 2.2. Measurements
X-ray diffraction (XRD) measurements were carried out on a Bruker-AXS D2 Phaser Desktop X-ray Diffractometer with a Lynx-Eye detector using CuKα radiation at 30 kV and 10 mA (λ = 1.5406 Å). The patterns were measured with a scan step time of 3 s and step size of 0.02°. The scanning electron microscope (SEM) images were obtained using Model S-4300SE (Hitachi Co., Ltd.). The textural properties were investigated by nitrogen adsorption-desorption isotherms at -196℃ using a gas adsorption analyzer (Model BEL-SORP, BEL Co., Ltd.). The samples were degassed at 200℃ for 6 h before the measurement. The hydrogen storage capacity was measured by using a gas adsorption analyzer (Model BEL-SORP, BEL Co., Ltd.) at 77 K and 1 bar. We used ultrahigh purity hydrogen (99.9999%) in order to reduce the influence of other impurities and used the volumetric measurement method to determine the hydrogen storage capacity.
3. Results and Discussion
- 3.1. Characterization
The XRD patterns of BCA and K-T-BCAs are shown in Fig. 1 . They show typical and almost identical carbon peaks. After chemical activation, the peak intensities for carbon at 23° and 44° decreased, because KOH destroys the microstructure of the biomass-derived activated carbons. This mechanism of activation by KOH has been reported previously [23 , 24] and is summarized below:
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X-ray diffraction patterns of biomass-derived carbon (BCA) and K-T-BCAs: (a) BCA, (b) K-700-BCA, (c) K-800-BCA, and (d) K-900-BCA.
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Potassium is produced during K 2 O activation at a high temperature, and it was found that the formation of pores was due to the loss of carbon. The SEM images that are shown in Fig. 2 also indicate the effects of the activation temperature. It can be seen that KOH activation changed the sample particle size and fineness. K-900-BCA has fine particles and regular granules compared with the other K-T-BCAs and BCA. This might be attributed to the erosion of BCAs caused by the higher activation temperature.
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Scanning electron microscopy images of biomass-derived carbon (BCA) and K-T-BCAs: (a) BCA, (b) K-700-BCA, (c) K-800-BCA, and (d) K-900-BCA.
Fig. 3 shows the nitrogen adsorption-desorption isotherms at 77 K. BCA and K-T-BCAs appear to have Type 1 isotherms without a noticeable hysteresis loop, which is typical of physisorption in microporous materials [25] . Most of the pores were filled below a relative pressure of about 0.1, indicating that these samples have high microporosity. However, K-800-BCA and K-900-BCA show a slight hysteresis loop and increased adsorption volume of nitrogen at a relative pressure of about 1.0. These results show that the microstructure was destroyed and the macropores were formed at higher activation temperatures.
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N2/77 K adsorption-desorption isotherms of biomass-derived carbon (BCA) and K-T-BCAs.
Fig. 4 shows mesopore and micropore size distributions of BCA and K-T-BCAs. The BCA and K-T-BCAs have similar peaks, but K-900-BCA has the highest peak intensity with most pores <1 nm. Moreover, K-900-BCA shows a relatively high peak intensity above a pore diameter of 50 nm; these results correspond with Fig. 3 .
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Mesopore and micropore size distribution of biomass-derived carbon (BCA) and K-T-BCAs.
In order to understand the pore structures of the BCA and K-T-BCAs in detail, Table 1 shows the textural properties of BCA and K-T-BCAs. The specific surface area, total pore volume, and micropore volume of K-T-BCAs were influenced by the activation temperature. The specific surface area and pore volume of the samples increase as the activation temperature was increased. As expected, K-900-BCA has the highest specific surface area (1,753 m 2 g -1 ), total pore volume (1.229 cm 3 g -1 ), and micropore volume fraction (72.5%). The high specific surface area and good micropore volume fraction provide good conditions for hydrogen adsorption.
N2/77 K textural properties of BCA and K-T-BCAs
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BCA: biomass-derived carbon. SBET: specific surface area computed using Brunauer-Emmett-Teller equation at a relative pressure range of 0.005-0.04. VTotal: total pore volume is estimated at relative pressure P/P0 = 0.99. VMeso: mesopore volume determined from the Barrett-Joyner-Halenda equation. VMicro: micropore volume determined from the subtraction of mesopore volume from the total pore volume. FMicro: fraction of micropore volume = (micropore volume/total pore volume) × 100.
- 3.2. Hydrogen storage capacities
Fig. 5 shows the hydrogen storage capacities of BCA and K-T-BCAs at 77 K and 1 bar with various sample activation temperatures. K-900-BCA has the highest hydrogen storage capacity of 2.7 wt%. The corresponding values for K-800-BCA, K-700-BCA, and BCA are 2.5, 1.9, and 1.1 wt%, respectively. As can be seen from the results of textural properties, K-900-BCA has the highest specific surface area and micropore volume, and therefore, it has the highest hydrogen storage capacity. These results show that KOH greatly affects carbons at high temperatures. The hydrogen adsorption of the porous carbon materials strongly depended on their microporosity, and the results of these experiments correspond with an earlier report [26] . The hydrogen storage of BCA and K-T-BCAs was also influenced by the microporosity of the samples, which can be enhanced by activation.
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Hydrogen storage behaviors of biomass-derived carbon (BCA) and K-T-BCAs at 77 K and 1 bar.
4. Conclusions
In this study, we prepared biomass-derived activated carbons using watermelon flesh and a hydrothermal reaction, followed by chemical activation with KOH at various temperatures. The obtained porous carbons had specific surface areas in the range 419-1753 m 2 g -1 and micropore volumes in the range 0.044-0.547 cm 3 g -1 . The results show that the specific surface area and micropore volume were influenced by the activation temperature. K-900-BCA showed the highest specific surface area (1753 m 2 g -1 ) and micropore volume (0.547 cm 3 g -1 ). Therefore, K-900-BCA has the highest hydrogen storage capacity, amounting to 2.7 wt% at 77 K and 1 bar. Thus, K-900-BCA can be used as a potential hydrogen storage material and can be enhanced with other metal doping or surface functionalization to increase its hydrogen storage capacity.
This work was supported by the Carbon Valley Project by Ministry of Trade, Industry and Energy, Republic of Korea
Liu C , Fan YY , Liu M , Cong HT , Cheng HM , Dresselhaus MS. 1999 Hydrogen storage in single-walled carbon nanotubes at room temperature Science1127 286 1127 -
Im JS , Park SJ , Kim TJ , Kim YH , Lee YS. 2007 The study of controlling pore size on electrospun carbon nanofibers for hydrogen adsorption J Colloid Sci 318 42 -
Kim BJ , Lee YS , Park SJ. 2008 A study on the hydrogen storage capacity of Ni-plated porous carbon nanofibers Int J Hydrogen Energy 33 4112 -    DOI : 10.1016/j.ijhydene.2008.05.077
Ao Z , Dou S , Xu Z , Jiang Q , Wang G. 2014 Hydrogen storage in porous graphene with Al decoration Int J Hydrogen Energy 39 16244 -    DOI : 10.1016/j.ijhydene.2014.01.044
Kim BJ , Lee YS , Park SJ. 2008 Novel porous carbons synthesized from polymeric precursors for hydrogen storage Int J Hydrogen Energy 33 2254 -    DOI : 10.1016/j.ijhydene.2008.02.019
Silambarasan D , Surya VJ , Vasu V , Iyakutti K. 2013 Single walled carbon nanotubes-metal oxide nanocomposites for reversible and reproducible storage of hydrogen ACS Appl Mater Interfaces 5 11419 -    DOI : 10.1021/am403662t
Jung MJ , Kim JW , Im JS , Park SJ , Lee YS. 2009 Nitrogen and hydrogen adsorption of activated carbon fibers modified by fluorination J Ind Eng Chem 15 410 -    DOI : 10.1016/j.jiec.2008.11.001
Robertson C , Mokaya R. 2013 Microporous activated carbon aerogels via a simple subcritical drying route for CO2 capture and hydrogen storage Microporous Mesoporous Mater 179 151 -    DOI : 10.1016/j.micromeso.2013.05.025
Lee SY , Park SJ. 2011 Effect of platinum doping of activated carbon on hydrogen storage behaviors of metal-organic frameworks-5 Int J Hydrogen Energy 36 8381 -    DOI : 10.1016/j.ijhydene.2011.03.038
Lee SY , Park SJ. 2010 Hydrogen storage behaviors of platinum-supported multi-walled carbon nanotubes Int J Hydrogen Energy 35 13048 -    DOI : 10.1016/j.ijhydene.2010.04.083
Lee SY , Park SJ. 2011 Preparation and characterization of ordered porous carbons for increasing hydrogen storage behaviors J Solid State Chem 184 2655 -    DOI : 10.1016/j.jssc.2011.07.034
Cho JH , Yang SJ , Lee K , Park CR. 2011 Si-doping effect on the enhanced hydrogen storage of single walled carbon nanotubes and graphene Int J Hydrogen Energy 36 12286 -    DOI : 10.1016/j.ijhydene.2011.06.110
Gogotsi Y , Portet C , Osswald S , Simmons JM , Yildirim T , Laudisio G , Fischer JE. 2009 Importance of pore size in high-pressure hydrogen storage by porous carbons Int J Hydrogen Energy 34 6314 -    DOI : 10.1016/j.ijhydene.2009.05.073
Yang SJ , Kim T , Im JH , Kim YS , Lee K , Jung H , Park CR. 2012 MOF-derived hierarchically porous carbon with exceptional porosity and hydrogen storage capacity Chem Mater 24 464 -    DOI : 10.1021/cm202554j
Lee SY , Park SJ. 2012 Synthesis of zeolite-casted microporous carbons and their hydrogen storage capacity J Colloid Interface Sci 384 116 -    DOI : 10.1016/j.jcis.2012.06.058
Cho EA , Lee SY , Park SJ. 2014 Effect of microporosity on nitrogen-doped microporous carbons for electrode of supercapacitor Carbon Lett 15 210 -    DOI : 10.5714/CL.2014.15.3.210
Lee SY , Park SJ. A review on solid adsorbents for carbon dioxide capture J Ind Eng Chem In press
Zhang C , Geng Z , Cai M , Zhang J , Liu X , Xin H , Ma J. 2013 Microstructure regulation of super activated carbon from biomass source corncob with enhanced hydrogen uptake Int J Hydrogen Energy 38 9243 -    DOI : 10.1016/j.ijhydene.2013.04.163
Xiao Y , Chen H , Zheng M , Dong H , Lei B , Liu Y. 2014 Porous carbon with ultrahigh specific surface area derived from biomass rice hull Mater Lett 116 185 -    DOI : 10.1016/j.matlet.2013.11.007
Hayashi J , Kazehaya A , Muroyama K , Watkinson AP. 2000 Preparation of activated carbon from lignin by chemical activation Carbon 38 1873 -    DOI : 10.1016/S0008-6223(00)00027-0
Foo KY , Hameed BH. 2012 Preparation of activated carbon by microwave heating of langsat (Lansium domesticum) empty fruit bunch waste Bioresour Technol 116 522 -    DOI : 10.1016/j.biortech.2012.03.123
Wu XL , Wen T , Guo HL , Yang S , Wang X , Xu AW. 2013 Biomass-derived sponge-like carbonaceous hydrogelsand aerogels for supercapacitors ACS Nano 7 3589 -    DOI : 10.1021/nn400566d
Kim YH , Park SJ. 2011 Roles of nanosized Fe3O4 on supercapacitive properties of carbon nanotubes Curr Appl Phys 11 462 -    DOI : 10.1016/j.cap.2010.08.018
Meng LY , Park SJ. 2010 Effect of heat treatment on CO2 adsorption of KOH-activated graphite nanofibers J Colloid Interface Sci 352 498 -    DOI : 10.1016/j.jcis.2010.08.048
Sing KSW. 2009 Reporting physisorption data for gas/solid systems with special reference to the determine of surface area and porosity Pure Appl Chem 54 2201 -
Chen CH , Huang CC. 2007 Hydrogen storage by KOH-modified multi-walled carbon nanotubes Int J Hydrogen Energy 32 237 -