carbon nano structures an efficient hydrogen storage medium

8/7/2019 Carbon Nano Structures an Efficient Hydrogen Storage Medium

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CARBON NANOSTRUCTURES: AN EFFICIENT

HYDROGEN STORAGE MEDIUM

FOR FUEL CELLS

Document BySANTOSH BHARADWAJ REDDY

Email: [email protected]

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ABSTRACT

The science of nanotechnology, now a days is leaving trademark prospects for betterliving. The motto of nanotechnology is ever smaller and ever faster. In this territory or field ithas also encroached its arms into reach and development of hydrogen fuel cells. Carbon

nanotubes have been intensively investigated for their fundamental technical importance for

hydrogen storage. New techniques being researched may soon make hydrogen storage morecompact safe and efficient. This is accomplished by using various approaches to shape carbon

into microscopic cylindrical structures known as nanotubes and nanofibers, molecular cousins of

buck minister fullerene (C60) or bucky balls. One of the critical factors in nanotubesusefulness as a hydrogen storage medium is the ratio of stored hydrogen to carbon.

Developing high-density hydrogen system, about 5-wt% that can release hydrogen at a

temperature lower than 1000C has been the focus and the goal of researchers. The basic current

approaches of hydrogen storage a compressed gas, liquid or in the form of solid hydrogen. Asolid hydrogen storage system is reliable, sample to engineer and tremendously safer. Our

objective has been to utilize the physisorption effect and generate chemisorption effect by

introducing transition metals and hydrogen bonding clusters is expected to allow us to tune thematerial for hydrogen sorption at desired temperature and pressures.

Carbon nanotechnology represents a new direction for solid hydrogen storage.

Especially, if these materials can be altered to store large amounts of hydrogen at roomtemperature, samples have been doped and spectroscopic characterization was conducted. These
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impeded clusters are capable of bonding large amounts of hydrogen with

thermodynamic and enhanced kinetics, while the transition metals catalyze the hydrogen to react

with clusters or nanotubes systems.

INTRODUCTION:


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H2 - fuel of the future***_Hydrogen Guide by async_ ***

http://asyncbrain.baf.cz | [email protected]

Note that this document is a mixture of the web sites' texts with my additional info.

To resolve global enviromental problems we must give up a carbon technology which isnot compensated by photosynthesis and simple inefficent combustion principles which

cause an emmisions of NOx, SOx, dust,... and other fragments of hydrocarbons.

Hydrogen is one way:

Why H2 as basic element of global solution of powering?

When using a hydrogen as the chemical energy storage after reaction with oxygenwe get energy (heat, electricty, other chemicals...) and pure water which is

automatically recycled via atmospehere and hydrospehere.

Hydrogen is the lightnest element on the world and has approx. 2.5-5 timeshighest energy density than other fuels used nowdays.

Hydrogen has no negative influence on the nature/enviroment. Hydrogen "energy transportation/storage" cycle produce no CO2 or no other

greenhouse gases as methane. We must realize that usage of methane or naturalgas is associated with CH4 emmisions. Note that coal mining produce greenhouse

methane and other poison gases as Rn.

General problems with hydrogen production, handling and comercialization:

Cheap oil and natural gas. Hydrogen storage and infrastructure due to high explosivity of H2+O2 mixture. Money and consumerism. Producing hydrogen is well known in diferent kinds. H2 transformation to

eletrical energy is developed too (fuell cells).

Hydrogen properties:

izotopes1

1H,2

1H (deuterium D),3

1H (tritium T)

molecule H-H

melting temperature @100kPa -259.14 degC

boiling temperature @100kPa -252.8 degC

critical temp&pressure -239.92 degC @ 1.297MPa

specific heat14.189kJ.Kg^-1.K^-1 (approx 3.4x higher than

water)


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Hydrogen as a fuel, particularly for automotive applications, is attractive because of thehigh energy value and lack of environmental pollutants generated on combustion, compared with

conventional fossil fuel sources. However, there are a number of obstacles that have yet to be

over come. The issue discussed in this paper relates to that of storage, yet there are also questionsof how to economically produce the hydrogen, practical distribution methods, and the creation of

international standards that must be addressed. Putting aside the notion that hydrogen may be

directly combusted in a modified engine, the other option for hydrogen power is a fuel cell,where an electro chemical reaction generates the necessary energy. We want an inexpensive low-

weight fuel cell system with a hydrogen storage device capable of quick loading and unloading,

comparable in volume to conventional gasoline tanks.Popular research avenues for automotive hydrogen storage systems include

1. physical storage via liquefaction or compression,

2. chemical storage in irreversible hydrogen carriers (such as methanol),

3. reversible metal and chemical hydrides and

4. gas on solid absorption.Whatever the medium, the bench mark has been set at 6.5 wt% (the ratio of stored hydrogen

weight to system weight) and a volumetric density of 62 Kg H2/m3.

HYDROGEN STORAGE TECHNOLOGIES:

Hydrogen storage and transporation methods:

see also DERA's concepts:http://www.h2net.org.uk/PDFs/Stor2000/H2nettalk_Nov00.pdf

One of the greatest problems connected with hydrogen was the method of its storage. The very

high explosiveness of this gas, forced scientists to work intensively on developing new safe way

of its lying in. We can distinguish the following ways of hydrogen storage:

Compressed in the gas vessel

This method may be applied only in stationary usage because of the danger of explosion andhigh weight of the vessel. This process requires energy to accomplish and the space that the

compressed gas occupies is usually quite large resulting in a lower energy density when

compared to a traditional gasoline tank. A hydrogen gas tank that contained a store of energy

equivalent to a gasoline tank would be more than 3,000 times bigger than the gasoline tank.Hydrogen can be compressed into high-pressure tanks where each additional cubic foot

compressed into the same space requires another atmosphere of pressure of 14.7 psi. High-

pressure tanks achieve 6,000 psi, and therefore must be periodically tested and inspected toensure their safety.

Traditional steel cylinders:

heavy, typically


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much lighter than steel cylinders, ca. 3 wt % (560 Wh/kg)

Ultra high pressure composite cylinders, ca. 10 wt% (1860 Wh/kg)

LLNL/IMPCO tested 11 wt % cylinder @ 350 bar (2100 Wh/kg)

Bulky storage method

User resistance to high pressure cylinders

Composite cyclinders (DERA):

Vessels (Air Products PLC, Hydrogen Production Workshop University of Glamorgan 14

February 2001):

Liquid form (LH2)

Liquid Hydrogen Hydrogen does exist in a liquid state, but only at extremely cold temperatures.

Liquid hydrogen typically has to be stored at 20K or -253C. The temperature requirements forliquid hydrogen storage necessitate expending energy to compress and chill the hydrogen into its

liquid state. The cooling and compressing process requires energy, resulting in a net loss of about30% of the energy that the liquid hydrogen is storing. The storage tanks are insulated, to preserve

temperature, and reinforced to store the liquid hydrogen under pressure.

Combine the energy required for the process to get hydrogen into its liquid state and the tanksrequired to sustain the storage pressure and temperature and liquid hydrogen storage becomes


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very expensive comparative to other methods. Research in the field of liquid hydrogen storage

centers around the development of composite tank materials, resulting in lighter, stronger tanks,

and improved methods for liquefying hydrogen.

Liquid hydrogen storage/transport (Air Products PLC, Hydrogen Production Workshop

University of Glamorgan 14 February 2001):

Liquid Carrier StorageThis is the technical term for the hydrogen being stored in the fossil fuels that are common in

today's society. Whenever gasoline, natural gas methanol, etc.. is utilized as the source forhydrogen, the fossil fuel requires reforming. The reforming process removes the hydrogen from

the original fossil fuel. The reformed hydrogen is then cleaned of excess carbon monoxide,

which can poison certain types of fuel cells, and utilized by the fuel cell. Reformers are currentlyin the beta stage of their testing with many companies having operating prototypes in the field.

See hydrogen production>Steam methane reforming (SMR) @Hydrogen production section

Chemical bonding

It's similar to Liquid Carrier Storage. Many of these compounds are utilized as a hydrogen

storage method. The hydrogen is combined in a chemical reaction that creates a stable compoundcontaining the hydrogen. A second reaction occurs that releases the hydrogen, which is collected

and utilized by a fuel cell. The exact reaction employed varies from storage compound to storagecompound. Some examples of various techniques include ammonia cracking, partial oxidation,

methanol cracking, etc. These methods eliminate the need for a storage unit for the hydrogen

produced, where the hydrogen is produced on demand. The best weight percent efficiency for

secondary storage is approximately 20 % for BH3NH3, for which hydrogen release is achievedby thermal decomposition at 100-300 degC.

DERA's info:

Hydrolysis (reaction with water)

- Primary hydrides- e.g. LiH, LiBH 4 , NaBH 4

Thermolysis (decomposition by heat)

- NH4X + MH- NH3BH3

Metal hydrides
http://asyncbrain.baf.cz/sanatorium/1/h2fuel/#production%23productionhttp://asyncbrain.baf.cz/sanatorium/1/h2fuel/#production%23production


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Metal hydrides are specific combinations of metallic alloys that act similar to a sponge soaking

up water. Metal hydrides posses the unique ability to absorb hydrogen and release it later, either

at room temperature or through heating of the tank. The total amount of hydrogen absorbed isgenerally 1% - 2% of the total weight of the tank. Some metal hydrides are capable of storing 5%

- 7% of their own weight, but only when heated to temperatures of 2500 C or higher. The

percentage of gas absorbed to volume of the metal is still relatively low, but hydrides offer avaluable solution to hydrogen storage.

Metal hydride sorption and desorption formulae:

M + xH2 MH2x

Features:

Good volumetric performance: theoretical 100 g/L,1860 Wh/L.

Poorer gravimetric performance: theoretical 1-2 wt %, 186-370 Wh/kg.

Desorption endothermic - requires heat.

H2 stored at constant P - safe storage.

Metal hydrides offer the advantages of safely delivering hydrogen at a constant pressure. The life

of a metal hydride storage tank is directly related to the purity of the hydrogen it is storing. The

alloys act as a sponge, which absorbs hydrogen, but it also absorbs any impurities introducedinto the tank by the hydrogen. The result is the hydrogen released from the tank is extremely

pure, but the tank's lifetime and ability to store hydrogen is reduced as the impurities are left

behind and fill the spaces in the metal that the hydrogen once occupied. H2 could be purified viaceramic membranes:http://www.et.anl.gov/sections/ceramics/research/ceram_mem.html

One volumetric unit of lithium during the reaction with hydrogen is able to absorb about 1600

units of this gas. A significant improvement in storage efficiency is required for transportapplications, which in the case of a typical car has a fuel requirement of ~ 1 kg of H2 per 100 km

travelled.

Gravimetric curves:
http://www.et.anl.gov/sections/ceramics/research/ceram_mem.htmlhttp://www.et.anl.gov/sections/ceramics/research/ceram_mem.htmlhttp://www.et.anl.gov/sections/ceramics/research/ceram_mem.html


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Links:

buy your own metal-hydride tank (commerce):http://www.fuelcellstore.com/products/index/hydrogen_storage.html

Polymer-dispersed metal hydrides (PDMH)

http://www.eren.doe.gov/hydrogen/pdfs/30535aq.pdf

http://www.materiale.kemi.dtu.dk/hydrid/http://mstd.nrl.navy.mil/6320/6323/HydrogenStorage.html

Intermetalic compoundsA powder of an alloy of lanthanum with cobalt and samarium with nickel is able to absorb underthe pressure of 0.4 MPa (4 atm) such amount of hydrogen, which was able to store in the same

vessel but under the pressure of 100 MPa (1000 atm).

Glass Microspheres

Tiny hollow glass spheres can be used to safely store hydrogen. The glass spheres are warmed,

increasing the permeability of their walls, and filled by being immersed in high-pressure

hydrogen gas. The spheres are then cooled, locking the hydrogen inside of the glass balls. Asubsequent increase in temperature will release the hydrogen trapped in the spheres.

Microspheres have the potential to be very safe, resist contamination, and contain hydrogen at a

low pressure increasing the margin of safety.

DERA's info:

W.J.Schaffer have claimed capacities of > 10 % - pressures of 10,000 psi- permeable to H 2 at high temperatures (> 200 o C)

- impermeable at room temperature

- spheres produced by a single drop process

- slow, expensive
http://www.fuelcellstore.com/products/index/hydrogen_storage.htmlhttp://www.eren.doe.gov/hydrogen/pdfs/30535aq.pdfhttp://www.ltyr.com/applications/applications_hydrogen.htmlhttp://mstd.nrl.navy.mil/6320/6323/HydrogenStorage.htmlhttp://mstd.nrl.navy.mil/6320/6323/HydrogenStorage.htmlhttp://www.fuelcellstore.com/products/index/hydrogen_storage.htmlhttp://www.eren.doe.gov/hydrogen/pdfs/30535aq.pdfhttp://www.ltyr.com/applications/applications_hydrogen.htmlhttp://mstd.nrl.navy.mil/6320/6323/HydrogenStorage.html


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DERA tested commercial glass microspheres - average particle size 6 - 75 mm

- capacity of 0.9 wt % @ 1000 psi

- would equal 5.9 % @ 10,000 psi- unfortunately most spheres broke > 3000 psi

Conclusions - Commercial spheres not suited to H2 storage- Need perfect spheres, no defects

Microspheres:

Carbon nanotubes - sigle wall (SWNT), multi wall (MWNT)

keyword: fullerenes

Carbon nanotubes are microscopic tubes of carbon, two nanometers (billionths of a meter)

across, that store hydrogen in microscopic pores on the tubes and within the tube structures.Similar to metal hydrides in their mechanism for storing and releasing hydrogen, the advantage

of carbon nanotubes is the amount of hydrogen they are able to store. Carbon nanotubes are

capable of storing anywhere from 4.2% - to 65% of their own weight in hydrogen. A novel

mechanism of hydrogen storage in carbon nanotubes is proposed by using the density functionalcalculations. Several key intermediate states are identified for hydrogen adsorption. Up to the

coverage of 1.0, hydrogen atoms chemisorb on the nanotube wall with either an arch type or a

zigzag type. Then, hydrogen can be further stored inside the nanotubes at higher coverage as amolecular form. Hydrogen atoms can be inserted into the nanotubes through the tube wall via

flip-in and/or kick-in mechanism with activation barriers of 1.5 and 2.0 eV, respectively. In the

hydrogen extraction process, hydrogen molecules inside a nanotube firstly dissociates onto theinner wall with an activation barrier of 1.6 eV. Secondly, hydrogen atoms at the interior of the


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tube wall are further extracted to the outer wall by the flip-out mechanism with an activation

barrier of 2.0 eV.

Our studies of carbon nano-material adsorptive properties for hydrogen, containing ~ 70 w/w %

of SWNTs, showed that the materials were capable of absorbing ~ 3.5 w/w % of hydrogen at 100

atm at room temperature and evolving hydrogen at pressures drop down to 1 atm. Analysis ofscientific publications shows that the experimental data are often contradictory, however, a

comparative analysis of the systems for hydrogen storage on the whole shows that the parameters

of carbon nano-materials are close to those required for motor transport. The reason of theparameter discrepancy is the lack of reliable methods for carbon nano-materials certification,

namely, the content of SWNT and MWNT, the content of open tubes and the distribution in

diameter. Additionally, residual catalysts affect hydrogen sorption.

Single-walled carbon nanotubes (SWNT) hold great promises as hydrogen storage medium.

Their unique architecture makes them the best carbon-based adsorbent for hydrogen. It has been

predicted theoretically that gravimetric density of up to 16 weight percent of H2 and volumetricdensity of 160 kg/m3 of H2 can be stored in (10,10) SWNT. This value exceeds greatly the US

Department of Energy's energy density target of 6.5 weight percent and 62 kg/m3 for aneconomically viable vehicular hydrogen storage medium. This value has never been obtainedexperimentally in a reproducible way, creating much controversy in the field. This is because of

the lack of controls in the synthesis of SWNT, the lack of understanding of the effects of

chemical modifications through the purification processes, and the lack of understanding of how

molecular hydrogen interacts with SWNT.

ENER1 has the necessary experience and expertise to carry out studies of electrochemical

intercalation of Li and other alkali metals into carbon nano-materials. According to predictions,carbon nanotubes intercalated by Li can demonstrate high electrochemical capacity (up to 640

mAh/g) in the first cycles, though capacity can decrease in cycling.

==Carbon nanotubes in their single-walled form are typically around 1.3 nm in diameter and are on

the order of 100um in length. They occur in three different structural forms, with different

diameters, the proportions of which are difficult to control in synthesis. The three principalproduction methods are laser vaporisation of a Ni/Co-doped graphite target, DC arc using a

Ni/Y-doped graphite anode, and vapour growth using Fe, Co and Ni catalyst particles with a

hydrocarbon feedstock at 1000 degC. Of these methods, the DC arc has better scalability. The

storage potential of nanotubes is in the range of 2 - 14 hydrogen weight percent, with claims ofup to 72 weight percent made for graphitic nanofibres. Advantages of carbon nanostructures as

storage media include their low mass density, chemical stability (up to 900 degC in an inert

atmosphere)and fast sorption kinetics compared to metal hydrides, owing to the hydrogen uptake

being a surface rather than a bulk process. At present they suffer from the disadvantages of beingvery expensive to produce in practically useful quantities, difficulties in purification of raw

nanofibre material, and the need for low temperatures or high pressures to achieve high levels ofstorage.

DERA's info:

Store up to 10 wt % H 2


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Require either:

o high pressure (>100 bar)

o low temperature (< -100 o C)

Different forms

o MWNT

o SWNT

o capped

o uncapped

1-10 nm diameter

Links:

http://www.eren.doe.gov/hydrogen/pdfs/30535an.pdf

http://www.foresight.org/Conferences/MNT9/Abstracts/Simard/http://www.nanotube.org/abs/LeeSM.html

< hydrogen.html bkp5 k b faculty www.personal.psu.edu http:>

http://www.kjemi.uio.no/ecssc8/Final-pdf/OH5.pdfhttp://www.ener1.com/b_storage.shtml

Carbon nanofibers

DERA's info:

Developed by Northeastern University

Consist of stacked graphite plates

Thin fibres of 5-100 nm diameter and 5-100mm length

Spacing between planes (0.34 nm) perfect for H2 (H2 diameter of 0.29 nm)

Potentially store over 50 wt % H 2 (9300 Wh/kg)

Room temperature storage

High pressure requiredVapour grown carbon nanofibres:
http://www.eren.doe.gov/hydrogen/pdfs/30535an.pdfhttp://www.foresight.org/Conferences/MNT9/Abstracts/Simard/http://www.nanotube.org/abs/LeeSM.htmlhttp://www.personal.psu.edu/faculty/b/k/bkp5/hydrogen.htmlhttp://www.kjemi.uio.no/ecssc8/Final-pdf/OH5.pdfhttp://www.ener1.com/b_storage.shtmlhttp://www.eren.doe.gov/hydrogen/pdfs/30535an.pdfhttp://www.foresight.org/Conferences/MNT9/Abstracts/Simard/http://www.nanotube.org/abs/LeeSM.htmlhttp://www.personal.psu.edu/faculty/b/k/bkp5/hydrogen.htmlhttp://www.kjemi.uio.no/ecssc8/Final-pdf/OH5.pdfhttp://www.ener1.com/b_storage.shtml


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Although car manufacturers around the world has reached the prototype stage with fuelcell operated automobiles using some of these technologies, there is a long way to go before such

systems could be used for personal transport vehicles. For instance, a liquid hydrogen storage

system losses up to 1% a day by boiling and up to 30% during filling, as well as requiringinsulation to keep the hydrogen at 200K. The associated safety risks result in denial of access to

parking houses or garages.

Hydrides reduce the risk factors of gaseous or liquid hydrogen. However, the large

disorption energy required as well as the weight and cost of any resulting system makes itless than ideal for automotive applications. Gas absorption is an inherently safe method that may

attain the benchmark standards hence the considerable interests in nanostructured carbonmaterials. Carbon in other forms i.e. activated carbon has been extensively studied for itsstorage properties. This material was found to be ineffective for storing hydrogen, because only a

small percentage of the surface strongly interacted with the hydrogen molecules at ambient

temperature and pressure.The more recently discovered nanomaterials such as graphitic nanofibers (GNFs) and

carbon nanotubes (CNTs) have renewed attention on carbon as an absorbent. One would expect


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nanostructured carbon to be an ideal storage medium, because of its high surface area and

abundant pour volume.

GRPHITE NANOFIBERS (GNFs):

Starting the discussion with nanofibers, the unique properties of GNFs suggest that the

material is ideal for selective absorption. Grown by the decomposition of hydrocarbons or carbonmonoxide over metal catalysts, the fiber consists of graphene sheets aligned in a set direction

(directed by the choice of catalyst), three distinct structures may be produced: platelet, ribbon

and herringbone. The very high hydrogen storage densities which have been reported for theplatelet and herringbone forms exceeding 50wt% and 60wt%, respectively are inconsistent

with theory. Further attempts to reproduce such high hydrogen storage densities have failed, and

typically results of only 0.08wt% have been achieved. The extraordinary high results were later

suggested to be influenced by the presence of water vapor, which expanded the spacing between

the graphite layers (3.4 A0) to accept multiple layers of hydrogen.Reversible storage capacities in the range 4-7 wt% were observed in herringbone GNF

samples. After changing the GNF production process, the observed capacities dropped to


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by volumetric means, at room temperature and at a pressure of 10MPa. Further synthesizes by

different methods and at non-ambient conditions of 40atm (4MPa) pressure and a low

temperature of 800k (-1930C) yields high purity and the adsorption capacity rose to 8wt%. Theends of nanotube are removed to enable direct access of hydrogen molecule into the interior if

tube. Further work to develop a cutting technique that would produce short SWNTs with open

ends, resulted in samples with hydrogen adsorption capacities of 3.5-4.5 wt% at temperature and 0.07MPa pressure. This was further optimized to achieve capacities of 7 wt%,

determined by thermal desorption spectroscopy after loading at 0.067 MPa a

temperature. Although theoretical calculations predict that a range of 4-14 wt% hydrogenadsorption in carbon-based materials is possible, they do not clearly distinguish between

chemisorption and physisorption. Chemisorption (the covalent bonding of hydrogen) would

require high temperature and high energy for hydrogen release, where as any practical fuel cell

application would require low adsorption and desorption energies.

COMPARISION OF DIFFERENT STORAGE SYSTEMS:

MATERIAL TEMPERATURE

MPa 2

`

SWNT 100% 1330K (-1400C) 0.0

SWNT High purity Ambient SWNT 50% 3000K (270C)

SWNT high purity 800K (-1930C)

MWNT 300-7000K (27-4270C) Ambient

SWNT-TiAl0.1V0.04 Ambient SWNT-Ti-6Al-4V Ambient

SWNT-Fe Ambient SWNT ball milled in Ar Ambient SWNT ball milled in D2 Ambient

Li-CNT 473-6730K (200-4000C) 0.1

Li-CNT


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the SWNTs.a reported value of 1.5 wt5 using the same method, and no appreciable adsorption

(below 0.005 wt%) for sample sonicated with a stain lass steal probe. The above results cannot

reproduce its own earlier results, and is only achieving capacities of 2-4 wt% which, whetherreproducible or not, fall below the commercially determined benchmark of 6.5 wt%, the effective

storage is also effected by type of hydrogen i.e. wet or dry. The method of alkali-doping did

not lead to graphite intercalated with alkali ions, but to a complicated structure containing alkalioxides and hydroxides. Although the gravimetric results could be reproduced, they are now

interpreted as desorption an reabsorption of water rather than hydrogen storage.

SCOPE FOR THE FUTURE STUDY:

With the current state of art not providing a solution to the problem of an appropriate

storage medium, the reality of hydrogen powered fuel cells for large scale utilization by theautomotive industry remains distant. Just how distant is hard to judge, as researchers pursue

numerous leads to optimize carbon nanostructures for hydrogen storage. On a fundamental level,

there are still challenges to mass produce controlled nanostructures at reasonable cost. More

specifically, there are still unknowns as to exact adsorption/ desorption mechanism and thevolumetric capacity of carbon nanostructures. The answer may lie in generating tubes or fibers of

higher purity, specific diameter or predetermined properties such as semi conducting rather thanmetallic. The feasibility of a viable fuel cell for hydrogen based on carbon nanostructures remain

undetermined.

BIBILOGRAPHY:

1. A.C.DILLON & M.J. HEBEN, HYDROGEN STORAGE USING CARB

ADSORBENTS.2. A.CHAMBERS, C.PARK, R.T.K.BAKER & N.M.RODRIGUEZ, HYDROGEN

STORAGE IN GRAPHITE NANOFIBERS, J. PHYS. CHEM.REV., 102(22).3. FURTER STUIES OF THE INTERACTION OF HYDROGEN WITH GRPHITE

NANOFIBERS, J.PHYS.CHEM.R, 103(48).

4. www.eren.doe.gov.

5. INT.J.OF.HYDROGEN ENERGY, VOL. 20-28.6. FUEL CELLS BULLETIN NO.38.
http://www.eren.doe.gov/http://www.eren.doe.gov/http://www.eren.doe.gov/


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carbon nano structures an efficient hydrogen storage medium

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