Silicon Nanotubes Outperform Carbon Nanotubes for Hydrogen Storage
20 April 2008
|Modeled snapshots and gravimetric adsorption capacities of hydrogen in the silicon nanotube arrays (SiNT), top; and carbon nanotubes (CNT), bottom. T = 298 K and P = 2, 6, and 10 MPa. Click to enlarge.|
Researchers at the Beijing University of Chemical Technology (BUCT) have determined that silicon nanotubes can store hydrogen more efficiently than carbon nanotubes. Their study is published in the ACS’ Journal of Physical Chemistry C.
The paper is one of the latest in a growing set of research seeking to leverage nanotube structures for hydrogen storage. Although work on the hydrogen storage potential of carbon nanotubes has been underway since 1997, most efforts using those materials have failed to reach the US Department of Energy (DOE) target of 6 wt% for commercial application.
In the BUCT study, Dapeng Cao and his colleagues used a multiscale theoretical method, combining first-principle calculation and a grand canonical Monte Carlo (GCMC) simulation, to predict the adsorption capacity of hydrogen in silicon nanotube (SiNT) arrays at 298 K (24.85°C, 76.73°F) under pressures ranging from 1 to 10 MPa. In the multiscale method, the binding energy obtained from the first-principle calculation is used as an input in the GCMC simulation.
|Gravimetric adsorption isotherms of hydrogen. Click to enlarge.|
From the first-principle calculation, they found that the SiNT arrays exhibit much stronger attraction to hydrogen both inside and outside SiNTs, compared to isodiameter carbon nanotubes (CNTs). The subsequent GCMC simulations indicated that gravimetric adsorption capacities of hydrogen in the SiNT arrays reach up to 1.30, 2.33, and 2.88 wt% at 2, 6, and 10 MPa, respectively. This represent improvements of 106%, 65%, and 52% in the gravimetric adsorption capacity of hydrogen at P = 2, 6, and 10 MPa, respectively, compared to the isodiameter CNTs.
A paper published in 2006 in the ACS journal Nano Letters by a team from the University of Crete and the University of Athens used a multiscale theoretical approach to investigate hydrogen storage in silicon-carbon nanotubes (SiCNTs).
Ab initio calculations at the density functional level of theory (DFT) showed an increase of 20% in the binding energy of H2 in SiCNTs compared with pure carbon nanotubes (CNTs). Classical Monte Carlo simulation of the nanotube bundles showed an even larger increase of the storage capacity in SiCNTs, especially in low temperature and high-pressure conditions.
At 1, 5 and 10 MPa at 175 K (-98°C, -145°F), the SiCNT bundles showed 1.18, 2.82 and 3.68 wt% respectively, compared to 0.53, 1.92 and 3.03 wt% respectively for the CNT bundles.
Another paper published earlier this year by another China research team at the National University of Defense Technology synthesized SiCNTs from multiwalled carbon nanotubes (MWCNTs) via chemical vapor reaction (CVR) and purification. The SiCNTs were characterized by XRD, SEM and TEM. Hydrogen storage capacities measurements indicated that SiCNTs were superior to MWCNTs.
In reference to the work on silicon-carbon nanotubes, the BUCT researchers wrote:
Mpourmpakis et al.  reported the hydrogen adsorption capacity increases of the square SiC tube array by 46% and 21% at pressures of 5 and 10 MPa and T = 175 K, respectively, compared to that of the isodiameter CNTs. Obviously, our calculation indicates that the SiNTs present a higher hydrogen adsorption capacity than SiC nanotubes.
Jianhui Lan, Daojian Cheng, Dapeng Cao, and Wenchuan Wang; Silicon Nanotube as a Promising Candidate for Hydrogen Storage: From the First Principle Calculations to Grand Canonical Monte Carlo Simulations; J. Phys. Chem. C, 112 (14), 5598 -5604, 2008. DOI: 10.1021/jp711754h
Rong-an Hea, Zeng-yong Chub, Xiao-dong Li and Yong-min Si; Synthesis and Hydrogen Storage Capacity of SiC Nanotube; Key Engineering Materials Vols. 368-372 (2008) pp 647-649
Giannis Mpourmpakis, George E. Froudakis, George P. Lithoxoos, and Jannis Samios; SiC Nanotubes: A Novel Material for Hydrogen Storage; Nano Lett., 6 (8), 1581 -1583, 2006. DOI: 10.1021/nl0603911
Si outperfom C but not that much and they are still from the 6% target which remains elusive so far.
Posted by: Teehugger | 20 April 2008 at 12:59 PM
And more importantly, nano-silicon stores energy a hell of a lot better it's made into BATTERIES.
Posted by: GreyFlcn | 20 April 2008 at 01:56 PM
Yes the nano-wire of Si are a breakthrough but it is unclear if we will ever be able to make nano-wire at indusrial scale, I sincerly hope they succeed but it is a major challenge.
Posted by: Teehugger | 20 April 2008 at 02:26 PM
Do silicon nanotubes make a durable cathode for a Li-ion batteries that works after repeated charge and discharge cycles? That is the question that matters. Please give it a try!
Posted by: Dave | 20 April 2008 at 02:27 PM
Im a proponent of hydrogen electrolysis as a new way to have energy but if this thing can boost performance of litium ion battery 10x then i hope some will put on the market a car with such batteries and start pusching down the price of gasoline in montreal canada where i live and where im hack by the municipal goverment, the provincial goverment, the federal goverment and the us goverment. Just the north coreen don't hack me but it's because they are just hacking their own citizens.
Posted by: a.b | 20 April 2008 at 02:29 PM
The issue isnt getting to 6 or even 9$ you can do thst rsdu with compressed h2 simply by making the tanks a little wider.
Right now they are just looking for non high pressure methods so they can avoid the bother and cost of 10k or the bother and size of a slightly enlarged 5k tank.
But even without absorbant if they took a single volt fc tank of 2kg vap used 5k tanks instead and just doubled the diameter they would still get the full 300 range with just the one tank abd still have alot of trunk space. They just want more ab d vetter and why not they still have a decade before they realy need to nail it down anyway.
Posted by: wintermane | 20 April 2008 at 03:24 PM
I wish they'd spent even 10% of the money available for hydrogen storage R&D on methane storage instead.
Posted by: Rafael Seidl | 20 April 2008 at 04:38 PM
"I wish they'd spent even 10% of the money available for hydrogen storage R&D on methane storage instead."
But can't some of the adsorption materials that they use for hydrogen be used for methane as well?
Posted by: Gabe | 20 April 2008 at 05:23 PM
Methane is what, 25% hydrogen? Methanol is 9% usable hydrogen. Both are stored with relative ease compared to hydrogen and are available today. Indeed, they have been here for decades. They each CURRENTLY exceed the TARGET goal of 6% hydrogen. They are not shiny enough for new research though. It's all nano this, and nano that, and oooh, ahhh. Meanwhile, in our own backyard...
Posted by: Hybrid fan | 21 April 2008 at 04:06 AM
If you go to energtek.com you see that their adsorb tanks for NG are for motorcycles and 3 wheeled vehicles. I would sure like to see companies like this make them for cars. At only 500-1000 psi the car could get enough in a smaller tanks for 200 miles range. The compressor would cost less and the fuel is cheaper and cleaner. I just like the idea of fueling in the garage and no more gasoline stations.
Posted by: sjc | 21 April 2008 at 09:15 AM
The problem with using methanol,ethanol, natural gas, gas etc as a fuel for H2 engines,is that despite their hihg H2 contant, the fuel needs to be reformed (H2 cracked and liberated from C,O , N etc) these systems are complex, heavy and generally need long startup times. By the time you have built a reliable system, they are much heavier and costlier than a compressed tank. Compressed tanks have their own problems, simply doubling the space to get the range WILL pretty much eat up the full trunk of a vehicle- solid state materials are desirable in that they could improve the volumetric density and/or reduce operating pressure. Natural gas vehicles does not help long term, they still produce CO2 and geopolitically- the fuel still comes from a few areas ( it does nothing to achieve energy independence) which is just as important if not more so to the Gov as CO2 reductions
Posted by: H2 Storage Researcher | 21 April 2008 at 11:00 AM
Methane adsorption would be very useful. There is lots of methane about and it can be easily produced from agricultural waste.
It could be burned in conventional ICEs with little to no modification.
It would give you a second source of energy for transportation (after liquid HCs).
It is being flared off in some places - they might stop if there was a bigger market for it.
And it burns very cleanly, so would be good for use in cities.
And it could be used in PHEVs.
Posted by: mahonj | 21 April 2008 at 03:15 PM
I am an NG fan. I want to promote converting cars to dual fuel near my home. There are 10,000 commuter cars that drive 50 miles or more round trip 5 days per week. I think they would like $1 fuel instead of $4 fuel and it would clean the air. I would rather that they not drive so much at all, but one step at a time.
Posted by: sjc | 21 April 2008 at 08:23 PM
Right now a major supplier of methane is big oil. Both Shell and British Petroleum have expanding leases in pristine wilderness areas of the Canadian portion of the Flathead Valley (southeast corner BC into Montana). These coalbed methane wells are a high priority for oil but wreak eco-havoc on the landscape.
To increase methane as a general transport fuel must be preceded by sustainable production methods.
Posted by: gr | 22 April 2008 at 09:57 AM
We could run a million cars on NG and not increase the use of natural gas all that much. There are 7 million NG vehicles in the world and only 150,000 of them are in the U.S. I would guess most of those are large trucks and buses.
Honda started their NG efforts in fleet vehicles and then worked with FuelMaker to design and develop the Phill compressor for home use. The Honda Civic GX natural gas car is a very clean running automobile.
We can make methane from biomass, but to say we need cleaner sources before we do anything else may not be the way to go. Natural gas is used for so many things from home and building heating to electric power generation that a vast supply market is already there.
I would rather see more cars that run on natural gas that is cheaper and cleaner than continue to run on gasoline and diesel. We produce 85% of the natural gas that we use in the U.S., but we produce only about 30% of the oil that we use. 150 million cars are not going to convert to NG anytime soon if ever, but if it cleans the air and reduces oil imports, I think that it deserves consideration.
Posted by: sjc | 22 April 2008 at 12:08 PM