Micro Fuel Cells Get Closer to Replacing Batteries

Nov 17, 2008 By Lisa Zyga feature
Close-up image of silicon microchannels. In microDMFC fuel cells, methanol and air circulate in microscopic microchannels etched in silicon wafers, as shown here. Image credit: Steve Arscott.

(PhysOrg.com) -- Mobile electronics have the potential to offer digital luxuries beyond our imagination, but they will never get there on today’s lithium ion batteries. Power has been the weak spot in the development of more advanced mobile electronics, and the need for power will become even more important as devices feature more energy-sapping applications.

One alternative to lithium ion batteries is fuel cells, due to their advantage of a high energy density – potentially, sixteen times higher than lithium ion batteries. Although researchers have been working on fuel cells for several years, they still face several challenges.

In a recent study, a team of researchers has developed micro-sized direct methanol fuel cells (microDMFC) that achieve significantly improved fuel efficiency and maintain a good power density while operating at room temperature. The energy density (measured in watt-hours per liter) of the new fuel cells is 385 Wh/L, which is superior to lithium ions batteries’ value of 270 Wh/L.

The research, led by Dr. Steve Arscott at the Institute of Electronics, Microelectronics and Nanotechnology (IEMN) in France, working in collaboration with SHARP Corporation in Nara, Japan, is published in a recent issue of the Journal of Micromechanics and Microengineering, and a second study has been accepted to the Journal of Power Sources.

Both studies use methanol fuel cells, in which methanol is the fuel and serves as the anode, while air is the oxidant and serves as the cathode. The methanol and air circulate through the fuel cell in microscopic microchannels etched in silicon wafers. When the methanol and air react in the presence of an electrolyte, electricity is produced.

In their second study, the researchers inserted a novel macroporous layer into the silicon-based microfuel cell. This design helped them improve the fuel efficiency from an already high 20 percent in their first study to 75 percent, while operating at room temperature. At this efficiency, the cells had a power density of 4.3 mW/cm2 and 9.25 mW/cm2 in the two respective studies. By adding a little bit more fuel, the researchers could increase the cells’ power density to 12.7 mW/cm2, although the efficiency then dropped to 20 percent (numbers are from the second study).

While previous fuel cells have achieved higher power density (up to 47.2 mW/cm2, by Yen et al), they haven’t operated at room temperature, which is absolutely essential for a commercial product.

Part of the reason that the new fuel cell achieves unprecedented fuel efficiency is because it uses a small amount of fuel (as little as 1.38 microliters per minute, or 550 nanoliters per minute, in the first and second study, respectively). By using a minimal amount of fuel, it’s possible to eliminate components such as pumps, which in turn would lower the cell’s energy consumption. However, as the researchers demonstrated, a minimum amount of fuel is necessary to maintain a steady fuel concentration across the cell to achieve maximum efficiency.

From the design perspective, the key to achieving high power density at room temperature is reducing both the fuel cell size and microchannel cross-sections. These modifications resulted in overall device miniaturization to a size of 0.18 cm2, with a thickness of 0.17 cm, corresponding to a tiny cell volume of 0.03 cm3 and a weight of about 110 milligrams. According to Arscott, these microcells are the smallest and lightest high-performance microDMFC working at room temperature to date.

Despite these improvements, challenges still remain, as Arscott highlighted.

“The biggest challenges facing micro fuel cells are: (i) high-performance room-temperature operation, (ii) miniaturization for on-chip use, (iii) compatibility with existing system fabrication (CMOS, for example), (iv) avoidance of complicated pumps for fuel and air which use energy themselves, (v) use of an efficient silicon-based proton exchange membrane and diffusion layers (novel porous layers for example), (vi) full integration with a microchannel architecture and also (vii) fuel storage,” he told PhysOrg.com. “On the latter point, obviously the more fuel efficient the cell, the less fuel needs to be stored for a given working period.”

In addition to applications in mobile consumer devices, the fuel cells could also be integrated as on-chip energy sources for autonomous MEMS and NEMS devices, as well as for sensors and actuators in silicon microelectronics, where efficient fuel use will be important. Arscott explained that different kinds of applications will require different kinds of fuel cells.

“In terms of fuel cells and energy sources, one must compare like with like: on one hand, fuel cells which will be one day be used for automobiles will be large and will have to supply a high power and have an energy density for a long journey,” he said. “On the other hand, micro fuel cells for a new generation of autonomous MEMS/NEMS-based sensors and actuators will require compact, on-chip, very efficient, high energy density energy sources which can supply micro and milliwatts for a long time. In the latter case, the energy required will be to drive the sensor and to communicate with the environment (for example, send a signal which says ‘forest fire here!’). I don't think there will be one dominant fuel cell for all applications, but there is likely to be one dominant fuel cell per application, for example, the hydrogen cell for cars or the methanol cell for portable and autonomous micro/nanosystems.”

Based on the progress of fuel cell research, fuel cells may begin widely replacing lithium ion batteries in consumer devices in the near future.

“From a research point of view, prediction is very hard,” Arscott said. “One can see fuel cells powering consumer electronics (iPod, Blackberry, etc.) in the next few years; one can see fuel cells powering automobiles in the next 20 years (or not, if we find huge resources of petrol in the Arctic, for example). The popularity and success of something is based on many factors – for example, cost (energy/dollar), availability, performance and the lawmakers. For instance, a ban on existing polluting batteries that contain heavy metals would favor fuel cells.

“One thing is sure,” he added. “Like everyone, I think that energy is about to become very important and, as Mark Twain (of who I'm a big fan) said, ‘What is a government without energy? And what is a man without energy? Nothing, nothing at all...’”

More information: Kamitani, Ai; Morishita, Satoshi; Kotaki, Hiroshi; and Arscott, Steve. “Miniaturized microDMFC using silicon microsystems techniques: performances at low fuel flow rates.” J. Micromech. Microeng. 18 (2008) 125019 (9pp)

Kamitani, Ai; Morishita, Satoshi; Kotaki, Hiroshi; and Arscott, Steve. “Improved fuel use efficiency in microchannel based DMFC using a hydrophilic macroporous layer.” J. Power Sources. To be published.

Copyright 2008 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

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User comments : 16

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Arkaleus
2.9 / 5 (9) Nov 17, 2008
I hear a lot from doomsayers who love to scare us all with energy depletion fairy tales. There is abundant energy available on earth - the problem is the delivery system. Petroleum is a vertically integrated monopoly and this keeps prices high and is subject to manipulation. Petroleum scarcity may be exaggerated and amplified by media propaganda, just like the hysterical crisis manufactured around "climate change." Both lies are made for a simple reason - to increase the flow of money from my wallet to theirs.

As the amount of energy required to run our devices goes down, we'll see less and less of the prophets of doom who think we're headed back to horses and oxen.

We've only begun to explore other means of generating electricity - and that's what it will eventually be all about. Combustion will be a thing of past and everything will be powered by electricity.
MGraser
3.1 / 5 (7) Nov 17, 2008
I think we should shut down all research, because the world is a bunch of doomsayers and we really have unlimited resources forever and ever without end...amen. Huh?
holmstar
4.1 / 5 (11) Nov 17, 2008
Both lies are made for a simple reason - to increase the flow of money from my wallet to theirs.


Just calling it a lie doesn't make it so. You don't convince anyone that disagrees with you with that kind of an argument.

As the amount of energy required to run our devices goes down, we'll see less and less of the prophets of doom who think we're headed back to horses and oxen.


While the power requirements of some devices are dropping, they are rising for others. Also, there are new devices appearing all the time and many are not replacements for current devices, but are all new and add to over-all power use. I doubt we are anywhere near saturation of electronic household devices, and I would be astounded if our power use drops any time soon (barring a massive recession/depression)

However, I do disagree with the "the earth can only support 200000 people! Oh NOES!" doomsayers.

Regardless, easily extractable oil is becoming hard to find. Most known reserves are already producing at or near maximum, and we are not currently finding enough oil to replace those reserves (at the same cost to produce). Thus, oil WILL become more expensive in the [not so?] long term.

We can either wait until oil is $300/barrel, or we can do something about it now and change our infrastructure to make use of alternative energy sources. We seem to agree on this last part.

physicsmonster
4 / 5 (6) Nov 17, 2008
Despite the previous unprofessional comments this looks like a step foward for tiny fuel cells
tpb
4.2 / 5 (6) Nov 17, 2008
power = 9.25 mW/cm2
size = 0.18 cm2
So this fuel cell is producing 1.66mW
Only 75 days to recharge your cell phone battery using this fuel cell.
Hopefully they can affordably make it 100 or 1000 times larger.
holmstar
4.3 / 5 (7) Nov 17, 2008
power = 9.25 mW/cm2
size = 0.18 cm2
So this fuel cell is producing 1.66mW
Only 75 days to recharge your cell phone battery using this fuel cell.
Hopefully they can affordably make it 100 or 1000 times larger.


Firstly... this cell isn't much bigger than a grain of sand! Thats amazing!

Secondly... think about it! you would use a whole bunch of these, not just one. In the space of a typical cell phone battery you could probably fit a few hundred of these.
physicsmonster
4.2 / 5 (5) Nov 17, 2008
I agree with holmstar lets not forget this is probably a prototype research battery and not yet in commercial production
tpb
2.5 / 5 (4) Nov 17, 2008
0.167" by 0.167" isn't a grain of sand.
To make this 100 times larger is 16.7" by 16.7"
holmstar
3 / 5 (5) Nov 17, 2008
0.167" by 0.167" isn't a grain of sand.
To make this 100 times larger is 16.7" by 16.7"


cm not inches. And there would be multiple layers (one layer is only 0.17 cm thick), so it wouldn't be 16.7 cm by 16.7 cm. if you used 4 layers you would only have a size of say 4cm x 4cm.
holmstar
2.7 / 5 (3) Nov 17, 2008
deleted
holmstar
4.3 / 5 (4) Nov 17, 2008
actually that would be 8 layers... my bad.

And actually 16.7cm x 16.7cm would be 1670 times larger than 0.167 x 0.167cm.
physpuppy
5 / 5 (3) Nov 17, 2008
actually that would be 8 layers... my bad.

And actually 16.7cm x 16.7cm would be 1670 times larger than 0.167 x 0.167cm.


Actually the statement made by tpb is little not well defined - "larger" meaning linearly larger? Larger by area taken up?

Assume by area:

0.167 x 0.167 cm = 0.0279 square cm.
An object 16.7x16.7 square cm = 278.9 square cm.
278.9/0.0279 = 10,000

So an object that is 16.7 x 16.7 is 10,000 times larger in area than an object 0.167 x 0.167 of the same units.

(In all of my physics courses, they always drilled: always go back to basic principles, even if that means doing - ugh - math :-) ...)

Ethelred
4.5 / 5 (2) Nov 18, 2008
Rats. Somebody beat me to fixing tpb's bad math.

100x100 /= 100 it equals 100 squared. Which is what counts when power is unit of area.
physicsmonster
5 / 5 (1) Nov 23, 2008
If the first comment posted is a joke about methane then DGBEACH should read the article as the writer is talking about methanol.
edwards
2 / 5 (1) Nov 30, 2008
These valuable marketing domains (web addresses) can be purchased at each website: MicroFueling.com, MicroFuel101.com, MicroFuelCellsInfo.com, microfuelbatteries.com and microfuelsystems.com.
Arkaleus
1 / 5 (1) Dec 23, 2008
Both lies are made for a simple reason - to increase the flow of money from my wallet to theirs.


You responded:

Just calling it a lie doesn't make it so. You don't convince anyone that disagrees with you with that kind of an argument.


If you deny that the prices of oil are based on lies, then I encourage you to research the peak oil phenomena a little better, and correlate the price of oil with the supposed supply curve of oil. You will find that the correlation is broken by a large enough degree to justify my suspicion of the price model explanation offered by peak oil hysterics.

Every "climate change" solution requires me to pay more money to some other person. Can you name one that does not eventually result in that condition?

As the amount of energy required to run our devices goes down, we'll see less and less of the prophets of doom who think we're headed back to horses and oxen.

While the power requirements of some devices are dropping, they are rising for others. Also, there are new devices appearing all the time and many are not replacements for current devices, but are all new and add to over-all power use. I doubt we are anywhere near saturation of electronic household devices, and I would be astounded if our power use drops any time soon (barring a massive recession/depression)


Generating electricity is and will always remain cheap and easy. This is why utilities remain in business. The trend in energy usage is not approaching cataclysm, it is slow and steady growth as population expands and efficiencies go up with it. Our energy generation technology can be powered by a large number of alternatives, and decentralization of energy generation is a real possibility in the near future.

Regardless, easily extractable oil is becoming hard to find. Most known reserves are already producing at or near maximum, and we are not currently finding enough oil to replace those reserves (at the same cost to produce). Thus, oil WILL become more expensive in the [not so?] long term.


Maybe. Do you trust the oil companies so much? Have you really estimated the natures of the men who run these industries correctly? My instinct tells me they will do whatever is required to keep the price of oil high while maximizing their political and social influence. Or do you understand human beings to operate under some other motivation?

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