New fuel cell design powered by graphene-wrapped nanocrystals

March 11, 2016 by Glenn Roberts Jr., Lawrence Berkeley National Laboratory
A powdery mixture of graphene-wrapped magnesium nanocrystals, produced at Berkeley Lab, is stable in air. The mixture's energy properties show promise for use in hydrogen fuel cells. Credit: Eun Seon Cho/Berkeley Lab

Hydrogen is the lightest and most plentiful element on Earth and in our universe. So it shouldn't be a big surprise that scientists are pursuing hydrogen as a clean, carbon-free, virtually limitless energy source for cars and for a range of other uses, from portable generators to telecommunications towers—with water as the only byproduct of combustion.

While there remain scientific challenges to making -based energy sources more competitive with current automotive propulsion systems and other energy technologies, researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a new materials recipe for a battery-like cell—which surrounds hydrogen-absorbing magnesium nanocrystals with atomically thin graphene sheets—to push its performance forward in key areas.

The graphene shields the nanocrystals from oxygen and moisture and contaminants, while tiny, natural holes allow the smaller hydrogen molecules to pass through. This filtering process overcomes common problems degrading the performance of metal hydrides for .

These graphene-encapsulated magnesium crystals act as "sponges" for hydrogen, offering a very compact and safe way to take in and store hydrogen. The nanocrystals also permit faster fueling, and reduce the overall "tank" size.

"Among metal hydride-based materials for hydrogen storage for vehicle applications, our materials have good performance in terms of capacity, reversibility, kinetics and stability," said Eun Seon Cho, a postdoctoral researcher at Berkeley Lab and lead author of a study related to the new fuel cell formula, published recently in Nature Communications.

Thin sheets of graphene oxide (red sheets) have natural, atomic-scale defects that allow hydrogen gas molecules to pass through while blocking larger molecules such as oxygen (O2) and water (H2O). Berkeley Lab researchers encapsulated nanoscale magnesium crystals (yellow) with graphene oxide sheets to produce a new formula for metal hydride fuel cells. Credit: Jeong Yun Kim

In a hydrogen fuel cell-powered vehicle using these materials, known as a "metal hydride" (hydrogen bound with a metal) fuel cell, hydrogen gas pumped into a vehicle would be chemically absorbed by the magnesium nanocrystaline powder and rendered safe at low pressures.

Jeff Urban, a Berkeley Lab staff scientist and co-author, said, "This work suggests the possibility of practical hydrogen storage and use in the future. I believe that these materials represent a generally applicable approach to stabilizing reactive materials while still harnessing their unique activity—concepts that could have wide-ranging applications for batteries, catalysis, and energetic materials."

The research, conducted at Berkeley Lab's Molecular Foundry and Advanced Light Source, is part of a National Lab Consortium, dubbed HyMARC (Hydrogen Materials—Advanced Research Consortium) that seeks safer and more cost-effective hydrogen storage, and Urban is Berkeley Lab's lead scientist for that effort.

The U.S. market share for all electric-drive vehicles in 2015, including full-electric, hybrids and plug-in hybrid vehicles, was 2.87 percent, which amounts to about 500,000 electric-drive vehicles out of total vehicle sales of about 17.4 million, according to statistics reported by the Electric Drive Transportation Association, a trade association promoting electric-drive vehicles.

Hydrogen-fuel-cell vehicles haven't yet made major in-roads in vehicle sales, though several major auto manufacturers including Toyota, Honda, and General Motors, have invested in developing hydrogen fuel-cell vehicles. Indeed, Toyota released a small-production model called the Mirai, which uses compressed-hydrogen tanks, last year in the U.S.

A potential advantage for hydrogen-fuel-cell vehicles, in addition to their reduced environmental impact over standard-fuel vehicles, is the high specific energy of hydrogen, which means that can potentially take up less weight than other battery systems and fuel sources while yielding more electrical energy.

A measure of the energy storage capacity per weight of hydrogen fuel cells, known as the "gravimetric energy density," is roughly three times that of gasoline. Urban noted that this important property, if effectively used, could extend the total vehicle range of hydrogen-based transportation, and extend the time between refueling for many other applications, too.

More R&D is needed to realize higher-capacity hydrogen storage for long-range vehicle applications that exceed the performance of existing electric-vehicle batteries, Cho said, and other applications may be better suited for hydrogen fuel cells in the short term, such as stationary power sources, forklifts and airport vehicles, portable power sources like laptop battery chargers, portable lighting, water and sewage pumps and emergency services equipment.

Cho said that a roadblock to metal hydride storage has been a relatively slow rate in taking in (absorption) and giving out (desorption) hydrogen during the cycling of the units. In fuel cells, separate chemical reactions involving hydrogen and oxygen produce a flow of electrons that are channeled as electric current, creating water as a byproduct.

The tiny size of the graphene-encapsulated nanocrystals created at Berkeley Lab, which measure only about 3-4 nanometers, or billionths of a meter across, is a key in the new fuel cell materials' fast capture and release of hydrogen, Cho said, as they have more surface area available for reactions than the same material would at larger sizes.

Another key is protecting the magnesium from exposure to air, which would render it unusable for the fuel cell, she added.

Working at The Molecular Foundry, researchers found a simple, scalable and cost-effective "one pan" technique to mix up the graphene sheets and magnesium oxide nanocrystals in the same batch. They later studied the coated nanocrystals' structure using X-rays at Berkeley Lab's Advanced Light Source. The X-ray studies showed how pumped into the fuel cell mixture reacted with the magnesium nanocrystals to form a more stable molecule called magnesium hydride while locking out oxygen from reaching the magnesium.

"It is stable in air, which is important," Cho said.

Next steps in the research will focus on using different types of catalysts—which can improve the speed and efficiency of chemical reactions—to further improve the fuel cell's conversion of electrical current, and in studying whether different types of material can also improve the fuel cell's overall capacity, Cho said.

Explore further: Could hydrogen vehicles take over as the 'green' car of choice?

More information: Eun Seon Cho et al. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage, Nature Communications (2016). DOI: 10.1038/ncomms10804

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MR166
2.3 / 5 (6) Mar 11, 2016
"So it shouldn't be a big surprise that scientists are pursuing hydrogen as a clean, carbon-free, virtually limitless energy source ...."

I wish that the Liberal Arts majors would stop trying to write articles about science. Their scientific ignorance is appalling!
Whydening Gyre
5 / 5 (3) Mar 11, 2016
And.... the problem with that sentence?
MR166
3.9 / 5 (7) Mar 11, 2016
And.... the problem with that sentence?


H2 is not a "Source" of energy it always takes more energy to produce it than it can deliver.
RealScience
5 / 5 (6) Mar 11, 2016
@WG - the problem with that sentence is that the hydrogen is not an energy source, it is an energy carrier.

Since we don't have hydrogen freely hanging around, we have to pry it from something that it is bound to, and that take energy. One choice is water - use energy to pry the hydrogen and oxygen apart, store the hydrogen in the graphite/magnesium, and then oxidize the hydrogen in a fuel cell to get energy. But since it takes at least as much energy to pry the hydrogen out of the water as you get from the fuel cell, you don't get net energy from the hydrogen so the hydrogen is not an energy SOURCE. (You can, however, release that energy when you want it, and that can be useful).

Another choice is to pry the hydrogen from natural gas, but there it is the natural gas that is the energy source. (Although technically even there millions-of-years-old solar energy is merely stored in the natural gas).

Ah - I see MR166 beat me to answering...
antialias_physorg
5 / 5 (5) Mar 12, 2016
H2 is not a "Source" of energy it always takes more energy to produce it than it can deliver.

By that definition neither oil nor coal (not even uranium) are energy sources.

Actually by that definition something like an 'energy source' doesn't exist at all.
Phys1
5 / 5 (4) Mar 12, 2016
hydrogen as a clean, carbon-free, virtually limitless energy source

Hydrogen is not a source of energy.
greenonions
5 / 5 (2) Mar 12, 2016
So it shouldn't be a big surprise that scientists are pursuing hydrogen as a clean, carbon-free, virtually limitless energy source
I have no problem with someone suggesting that scientists are 'pursuing' (researching) the idea that hydrogen has great potential in terms of powering cars etc. Yes - technically hydrogen is not considered an energy source - as it's EROI is less than 1. Real science explained that well above. All fuels have to be obtained and processed in some way - which takes energy. Tight oil and gas requires much more energy to obtain - than the easy stuff in the middle east. EROI is not the only metric to use when measuring the viability of an energy system. Cost is also interesting. If I can split water, and run a car on the hydrogen, and the cost per mile is less than a gasoline car - who cares if you want to parse the term 'source'? And look Mum - no nox and sox.
MR166
3 / 5 (4) Mar 12, 2016
" If I can split water, and run a car on the hydrogen, and the cost per mile is less than a gasoline car - who cares if you want to parse the term 'source'? And look Mum - no nox and sox."

I agree Onions, the bottom line is "Cost" in terms of both energy and economics. Right now batteries still look to be a better alternative. H2 is still a pipe dream. There is something about water coming out of a tailpipe that brings all the greenies to orgasm.
greenonions
5 / 5 (4) Mar 12, 2016
There is something about water coming out of a tailpipe that brings all the greenies to orgasm.
Maybe that is because they are concerned about the damage we are doing to the environment - and it is encouraging to see options that will do a better job - in terms of providing things like energy for our world - without the level of self destruction of fossil fuels.
RealScience
5 / 5 (5) Mar 12, 2016
By that definition neither oil nor coal (not even uranium) are energy sources.

Actually by that definition something like an 'energy source' doesn't exist at all.


Technically even uranium is the ashes of a dead star, so all this energy comes from the birth/expansion of the universe that led to stars.

But practically speaking, uranium is here on earth and can be mined with net delivered energy. Also coal, oil and natural gas can deliver net delivered energy, even if they really are just stored solar energy.

And the sun is shining whether we capture its energy or not, so solar, wind and hydroelectricity all can (and current do) have net delivered delivered energy.

In contrast oxidizing H2 does not have net delivered energy because it isn't already available on earth unoxidized (see CH4 semi-exception in first post).

What hydrogen CAN do is CARRY the energy and deliver it at a more useful time and place, and sometimes in a more useful form.
RealScience
5 / 5 (3) Mar 12, 2016
The article is also off base in claiming that hydrogen is the "most plentiful element on Earth".
Even if one counts the number of atoms rather than mass, it is beaten by oxygen, silicon, iron, magnesium, nickel, aluminum and probably sulfur.

(However there is no worry of running out since it is the most common element in water.)
Whydening Gyre
5 / 5 (1) Mar 12, 2016
"Source" was conferred in a relative way. I did not take it in the exact sense. I do understand the concept of "energy is never lost, only converted."
What about the rest of the article? Was it reasonably informative?
MR166
5 / 5 (1) Mar 12, 2016
"Source" was conferred in a relative way. I did not take it in the exact sense. I do understand the concept of "energy is never lost, only converted."
What about the rest of the article? Was it reasonably informative?


Yes it was except for the headline. This was another poorly thought out statement that creates the wrong impression.

In truth, if we could learn how to store H2 in a manner that does not require high pressures or low temperatures and equal the energy density and volumes of say gasoline, renewables will become our main source of energy.
MR166
5 / 5 (1) Mar 12, 2016
For instance, if H2 could be easily stored and transported then it would be profitable to produce it using solar and wind. Sometimes renewables have to be curtailed because they are producing more power than the grid can use. If this excess power could be converted in a usable transportation fuel then there would never be a need limit renewable power output. Any excess could used to produce the H2 feed stock and grid management would be greatly simplified. Transportation fuels are much more valuable per unit of energy than fuels that produce electricity.
Phys1
5 / 5 (1) Mar 12, 2016
If I can split water, and run a car on the hydrogen, and the cost per mile is less than a gasoline car - who cares if you want to parse the term 'source'? And look Mum - no nox and sox.

Fossil oil, hydrogen (by fusion), solar are sources of energy. This energy can be stored in H2 for later use, with less than 100% efficiency. H2 in is no more an energy source than a bottle of water is a water source. For marketing purposes, however, feel free to call it that.
Phys1
3.7 / 5 (3) Mar 12, 2016
" If I can split water, and run a car on the hydrogen, and the cost per mile is less than a gasoline car - who cares if you want to parse the term 'source'? And look Mum - no nox and sox."

I agree Onions, the bottom line is "Cost" in terms of both energy and economics. Right now batteries still look to be a better alternative. H2 is still a pipe dream. There is something about water coming out of a tailpipe that brings all the greenies to orgasm.

Water is coming out of any car exhaust pipe, as electrical cars do not have one. Moreover, hydrogen is a serious contender as an energy carrier. This is not activism but business. If you want to discuss orgasms, call a sex line. Please don't do so here unless in a scientific context.
MR166
5 / 5 (1) Mar 12, 2016
" Moreover, hydrogen is a serious contender as an energy carrier. "

Yea, just like fusion is a serious contender as a source of energy on earth. Please drop me a line when either become an economic reality.
Whydening Gyre
not rated yet Mar 12, 2016
Transportation fuels are much more valuable per unit of energy than fuels that produce electricity.

Think you meant transportable....
bluehigh
3 / 5 (2) Mar 12, 2016
Water vapour out the tailpipe could assist in cloud formation. That's good, right?

snerdguy
not rated yet Mar 14, 2016
I have read in the past about the development of a catalyst that makes separating hydrogen from water much more efficient. But, I see hydrogen fuel cells more as a mass energy storage system that will never be practical for vehicles. Hydrogen is not easy to handle, especially for the general public. Because it's odorless and colorless, a lot of fail safes would be needed. The tanks can also add a lot of weight to a vehicle because they have to withstand high pressures. Also, because of it's small molecular size, Hydrogen will be very prone to leaking away.

I see hydrogen as a medium that would allow wind and solar energy to be collected and stored in relatively distant places so it can be shipped for use in large stationary fuel cells connected to the power grid. Perhaps, it could be used for certain kinds of vehicles like trains and ships which are relatively stable and use electrical drive systems.
Feldagast
not rated yet Mar 17, 2016
How about separating and collecting both hydrogen and oxygen, pump them into cylinders and igniting them to drive a piston. End result is still water.
RealScience
5 / 5 (1) Mar 17, 2016
@Feldagast - That certainly works, and one doesn't even have to store the oxygen since air has plenty.

BUT for vehicles with cylinders one only gets the efficiency of an internal combustion engine instead of the roughly 2.5x higher efficiency of a fuel cell. Thus one would have to store ~2.5x the hydrogen. Since hydrogen storage is a big issue for vehicle, simply burring the hydrogen requires too big a tank to be practical (with today's storage).

For stationary power, combined-cycle natural-gas power plants are as efficient as fuel cells, and combined-cycle power plants cost much less per MW than fuel cells, so yes, burning the hydrogen (in a turbine rather than cylinders) is actually very reasonable.
(Fuel cells still have stationary uses - they scale down to kW, and can also ramp up and down faster than CC).
antialias_physorg
5 / 5 (3) Mar 17, 2016
Hydrogen is not easy to handle, especially for the general public. Because it's odorless and colorless

There are metal hydrides that don't outgas (under ambient conditions), so handling hydrogen can be quite safe/easy.

How about separating and collecting both hydrogen and oxygen, pump them into cylinders and igniting them to drive a piston. End result is still water.

BMW built a small series of such cars:
https://en.wikipe...drogen_7
But they are very inefficient.

Burning hydrogen also has the drawback that it produces water within a (lubricated) piston. Lubricants and water together don't make happy campers.
RealScience
not rated yet Mar 17, 2016

Burning hydrogen also has the drawback that it produces water within a (lubricated) piston. Lubricants and water together don't make happy campers.

Burning gasoline (mostly hexane = C6H14) produces roughly as many water molecules as carbon dioxide molecules (7 H2O for every 6 CO2), so water is already present in engine exhaust. The key is for the exhaust to be hot enough that the water doesn't condense until the tail pipe at the earliest.

But yes, inefficient.

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