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Northwestern-led team develops new MOFs with ultrahigh porosity for storage of hydrogen or methane for vehicles

A research team led by Northwestern University has designed and synthesized new metal-organic framework (MOF) materials with ultrahigh porosity and surface area for the storage of hydrogen and methane for fuel cell-powered vehicles. The designer materials can store significantly more hydrogen and methane than conventional adsorbent materials at much safer pressures and at much lower costs. A paper on their work is published in Science.

The ultraporous MOFs are based on metal trinuclear clusters, namely, NU-1501-M (M = Al or Fe). Relative to other ultraporous MOFs, NU-1501-Al exhibits concurrently a high gravimetric Brunauer−Emmett−Teller (BET) area of 7310 m2 g−1 and a volumetric BET area of 2060 m2 cm−3 while satisfying the four BET consistency criteria.

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NU-1501-M. Credit: Northwestern University


The high porosity and surface area of this MOF yielded impressive gravimetric and volumetric storage performances for hydrogen and methane: NU-1501-Al surpasses the gravimetric methane storage US Department of Energy target (0.5 g g−1) with an uptake of 0.66 g g−1 [262 cm3 (standard temperature and pressure, STP) cm−3] at 100 bar/270 K and a 5- to 100-bar working capacity of 0.60 g g−1 [238 cm3 (STP) cm−3] at 270 K; it also shows one of the best deliverable hydrogen capacities (14.0 weight %, 46.2 g liter−1) under a combined temperature and pressure swing (77 K/100 bar → 160 K/5 bar).

We’ve developed a better onboard storage method for hydrogen and methane gas for next-generation clean energy vehicles. To do this, we used chemical principles to design porous materials with precise atomic arrangement, thereby achieving ultrahigh porosity.

—Omar K. Farha, corresponding author

Adsorbents are porous solids which bind liquid or gaseous molecules to their surface. With its nanoscopic pores, a one-gram sample of the Northwestern material (with a volume of six M&Ms) has a surface area that would cover 1.3 football fields.

The new materials also could be a breakthrough for the gas storage industry at large, Farha said, because many industries and applications require the use of compressed gases such as oxygen, hydrogen, methane and others.

The ultraporous MOFs are built from organic molecules and metal ions or clusters which self-assemble to form multidimensional, highly crystalline, porous frameworks.

We can store tremendous amounts of hydrogen and methane within the pores of the MOFs and deliver them to the engine of the vehicle at lower pressures than needed for current fuel cell vehicles.

—Omar Farha

The Northwestern researchers conceived the idea of their MOFs and, in collaboration with computational modelers at the Colorado School of Mines, confirmed that this class of materials is very intriguing. Farha and his team then designed, synthesized and characterized the materials. They also collaborated with scientists at the National Institute for Standards and Technology (NIST) to conduct high-pressure gas sorption experiments.

Resources

  • Zhijie Chen, Penghao Li, Ryther Anderson, Xingjie Wang, Xuan Zhang, Lee Robison, Louis R. Redfern, Shinya Moribe, Timur Islamoglu, Diego A. Gómez-Gualdrón, Taner Yildirim, J. Fraser Stoddart, Omar K. Farha (2020) “Balancing volumetric and gravimetric uptake in highly porous materials for clean energy” Science doi: 10.1126/science.aaz8881

Comments

Davemart

I'm struggling with the scientific notation used.

Degrees Kelvin is OK, although the 270K given is pretty low, a chilly -3C

14%hydrogen by weight is excellent.

I have not however been able to decipher:

'46.2 g liter−1'

As negative exponents are:

'A negative exponent means how many times to divide by the number. Example: 8-1 = 1 ÷ 8 = 1/8 = 0.125. Or many divides: Example: 5-3 = 1 ÷ 5 ÷ 5 ÷ 5 = 0.008.'
https://www.mathsisfun.com/algebra/negative-exponents.html

That comes out to 0.02grams/litre, which makes no sense at all!

Where is the error?

Apologies for my lack of scientific background

James Lazar

'46.2 g liter−1' translates to "46.2 grams per Liter"

The "-1" exponent, just means to put the term "liter" in the denominator.

Hope this helps. - Jim

SJC_1

Correct, this could be used for big rig tractors.

Davemart

I'm still not following.

Putting the liter into the denominator came out to the 0.02 grams/liter I mentioned, which is tiny.

Simply, how much space is 1kg of hydrogen in this MOFC going to take up?

An FCEV has around 5-6kg on board.

Engineer-Poet

Davemart, you need to recognize that the superscript tag is not carried over in these copy-and-paste operations (and can't be inserted in comments either, a serious weakness of Typepad IMO).  If you're not clear on the meaning you can click through to the source text, when linked.

Davemart

@EP

The source text is not publically available, and since the difficulty I am having is the scientific notation, I expect it would not help me much anyway.

As I have said, can those familiar with it tell me how much space in litres a kilogram of hydrogen would take up?

Whatever shows up in comments, in Mikes post above it is plain that the claim is for 46.2 g liter to minus 1 exponent, so those familiar with the notation should be able to calculate from there.

I was not getting sensible figures from the calculation, so I obviously missed something.

gryf

46.2 grams per Liter @ 77 K (temperature of liquid nitrogen
From Toyota website (https://www.toyota.com/mirai/assets/core/Docs/Mirai%20Specs.pdf)
The 5 kg tanks (there are 2) have an internal volume of 122.4 liters, so 40.85 grams per liter. The MOF tanks have insulation which takes extra volume.

gryf

BTW gasoline is 748.9 grams per liter at 1 Bar.

Davemart

Thanks gryf

I found another link here:
https://phys.org/news/2020-04-gas-storage-method-next-generation-energy.html

Looking at the first diagram , not shown here, the volume is plain old 48g/litre, nothing about negative exponents and so on.

That comes out to around 100 litres for 5kg.

I don't know how practical the low temperatures would be for on board.

Engineer-Poet

46.2 g/liter is 0.0462 kg/liter.  To get liters per kilogram, take 1/x.  You get 21.6 l/kg.

Hollis McCray

I am completely confused by all of the above. Assuming I use the equivalent volume of a 15-gallon gasoline tank, which comes to approximately 57 liters. How much would that much of this material weigh? How much hydrogen would it store? And how would this compare in terms of energy to the equivalent volume of gasoline?

Davemart

@Hollis McCray

Fuel cell cars don't need the energy equivalent of gasoline to have decent range as fuel cells are a lot more efficient than a combustion engine to extract the energy.

Davemart

What I am unclear about is whether very low temperatures are needed to get the hydrogen into the MOF, or whether that low temperature needs to be maintained throughout storage.

Obviously in the latter case the utility is way less, enough I would have thought to make it impractical for on board storage at any rate in cars.

gryf

@Davemart
Low temperatures are needed to get reasonable capacity in MOF.
This was reported in GCC, where "researchers from the University of California, Berkeley and Lawrence Berkeley National Laboratory has used metal–organic frameworks (MOFs) to set a new record for hydrogen storage capacity under normal operating conditions" (https://www.greencarcongress.com/2018/12/20181206-mof.html).
As E-P pointed out then, liquid hydrogen has 70 g/liter density.
Maybe the MOF could be used in fuel cell ocean going vessels like ABB and Hydrogène de France are proposing, 77 K is close to LNG tank temperature and a lot easier to cool then LH2.

Davemart

Thanks gryf

Ptomzc

@Davemart
I've identified the source of your confusion. You were reading
46.2 g liter−1
as
(46.2 g liter)⁻¹

The intended meaning (with parentheses for clarity) was
46.2 g * (litre⁻¹)
which is the same as
46.2 g / litre

Engineer-Poet

How the heck did you manage a superscript here?

Hollis McCray

Alright, @davemart. I guess I was asking the wrong question. What I want to know is:

Will this give a hydrogen vehicle equivalent range to gasoline?

How much does one of these storage cells weigh per liter of volume?

It's probably early to ask this, but how practical will this be for mass production? Or is this a discovery that's a more distant precursor to a roadworthy application?

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