Daihatsu Develops Platinum-Free, Direct Hydrazine Fuel Cell Technology
14 September 2007
|Where the PEM fuel cell sends protons (H+) across the membrane, the Daihatsu cell sends anions (OH-) across its membrane. Click to enlarge.|
Daihatsu Motor, working with Japan’s National Institute of Advanced Industrial Science and Technology (AIST), has developed a new fundamental fuel cell technology: a platinum-free, direct hydrazine fuel cell (DHFC), which uses an anion-exchange polymer electrolyte.
Conventional PEM (proton exchange membrane) fuel cells for vehicles use strongly acidic electrolyte membranes and therefore must possess high corrosion resistance. The use of expensive platinum in the electrode catalyst material has been a common approach. Daihatsu essentially reversed the PEM model to create an alkaline anion exchange fuel cell. The new technology uses hydrazine hydrate (N2H4·H2O) as the fuel.
Where the PEM fuel cell sends protons (H+) across the membrane, the Daihatsu cell sends anions (OH-) across its membrane.
The Daihatsu technology uses alkaline electrolyte membranes, allowing the use of less expensive metals such as cobalt and nickel as an electrode catalyst (instead of platinum) and other inexpensive materials to be used in the separator and other component parts.
|Output and current densities from the new fuel cell. Click to enlarge.|
Using hydrazine hydrate as the fuel and the newly developed electrode catalyst, the new fuel cell can produce a high output of 0.5 W/cm2 (as measured by Daihatsu), which is comparable to the output obtained from a hydrogen fuel cell using platinum.
Since hydrazine hydrate is a liquid fuel, it is easy to handle during filling and its energy density is also high. However, high-concentration hydrazine hydrate is designated as a poisonous substance under Japan’s Poisonous and Deleterious Substances Control Law, and it must be handled under the same safety standards applicable to gasoline and most industrial chemicals.
|The hydrazine hydrate fueling system. Click to enlarge.|
Daihatsu developed a technology that fixes the hydrazine hydrate inside the fuel tank through the use of a polymer, minimizing the adverse effects that any dispersed fuel could have on humans or the environment should the fuel tank be damaged during a collision, but that makes the required amount of liquid hydrazine hydrate available in a timely manner for electricity generation in the fuel cell.
The fuel tank is filled with a granulized polymer embedded with carbonyl group (>C=O) for capturing the hydrazine hydrate. When the hydrazine hydrate enters the tank, it reacts with the carbonyl group (dehydration-condensation reaction) and bonds with the polymer, becoming a solid called hydrazone (>C= N2H2), which can be safely stored.
To release hydrazine hydrate from hydrazone, warm water circulates through the hydrazone (>C=N2H2), causing hydrolysis. This reaction returns the hydrazone to the original carbonyl group (>C=O), and releases liquid hydrazine hydrate (N2H4·H2O), which is then supplied to the fuel cell.
The new fuel cell system offers numerous benefits, according to Daihatsu, including resource conservation, low cost, high output, and safe and easy fuel handling. The company plans to accelerate further research and development of the technology.
Given the number of issues that must be addressed—including improvements in the polymer for fixing the fuel, enhancement of both the performance and durability of the fuel cell, and establishment of the necessary infrastructure—Daihatsu hopes to establish wide-ranging partnerships with relevant parties and proceed with further R&D.
A paper describing the technology is published in the journal Angewandte Chemie International Edition. The journal labelled the study a “Hot Paper.”
Daihatsu is the mini-vehicle unit of Toyota Motor.
Koichiro Asazawa, Koji Yamada, Hirohisa Tanaka, Akinori Oka, Masatoshi Taniguchi, Tetsuhiko Kobayashi; “A Platinum-Free Zero-Carbon-Emission Easy Fuelling Direct Hydrazine Fuel Cell for Vehicles”; Angewandte Chemie International Edition Published online, DOI: 10.1002/anie.200701334
Daihatsu technology backgrounder
A rocket fuel fuel cell. Hmmm.
Posted by: Derek | 14 September 2007 at 10:00 AM
Holy cow, lets take one of the most toxic substances we can find and make a fuel cell out of it...
Sheesh, I"ll stick with my plutonium powered radon exhaust powered tricycle. I use that to head over to the local Ice cream shop to get my coal dust uranium flavered ice cream!
Posted by: Cosmo | 14 September 2007 at 10:21 AM
Cosmo & Derek,
Please kindly restrain your negative emotions.
This a cause for joy and celebration. Yahoo!!!Yipidiyee!!!! :))))
Many disadvantages of FCV's using current PEM technology are being solved simultaneous here with Daihatsu's approach. Lower-cost fuel cell using catalysts more abundant and much cheaper than platinum will mean no problem equipping hundreds of millions of FCV affordably, unlike platinum which will restrict FCV to only a few millions.
And then, liquid fuel hydrazine hydrate stored in solid form on board the car will squelch any unreasonable concern regarding safety as with compressed hydrogen, while having much higher volumetric and gravimetric energy density.
Posted by: Roger Pham | 14 September 2007 at 10:39 AM
Hydrazine is a complete non-starter for large scale application, so the derision is not unwarranted. The manufacturing process is difficult and inefficient, and the material is a wonderful combination of poisonous, carcinogenic, explosive, flammable, and unstable. When used in aerospace (as in the emergency backup APUs on fighter jets) the maintenance requirements when the units are activated are quite expensive. On the space shuttle, workers at the landing have to dress in isolation suits to verify no hydrazine (derivative) vapors are coming off the vehicle before they let the astronauts out.
Posted by: Paul Dietz | 14 September 2007 at 10:53 AM
The other problem with this scheme, not mentioned at all in the article, is that you must not use untreated air in an alkaline fuel cell. CO2 in the air will be converted to carbonate, which will either neutralize the electrolyte or precipitate out and clog the cell.
Were it not for this, we could already have had alkaline fuel cells using nickel electrodes and consuming hydrogen gas.
Posted by: Paul Dietz | 14 September 2007 at 11:09 AM
I've seen companies that claim they have fixed the CO2 poisoning problem.
Posted by: Ben | 14 September 2007 at 12:41 PM
Is that the Ice Cream Shoppe that has the PCB Sprinkles?
Posted by: jcwinnie | 14 September 2007 at 01:19 PM
@ Ben -
interesting background article from Feb 2006. Given the relatively low R&D activity in AFC technology, chances are its assertions and conclusions still apply today - with the exception of this effort by Daihatsu.
On the whole, mildly pressurized AFC should be simpler, cheaper and more robust than than highly pressurized PEMFCs with similar performance. CO2 is a minor problem and anyhow only degrades the cheap liquid electrolyte (typically potassium lye, which is cycled to cool the stack) over many hours of operation. It could be replaced much like engine oil is in ICE technology. There is no risk of electrode poisoning or dangerous hot spots as in PEMFC technology.
Even so, Astris indicates an OEM price point of over $1000/kW system cost in modest unit volumes for its own atmospheric AFCs. This compares to just $50-$75/kW for an ICE. In practice, any vehicle equipped with any type of fuel cell will have to be exceptionally light to keep the power demand down.
For example, the upcoming Loremo compact 2+2 weighs just 450kg and can make do with diesel engines rated at 20-30kW and to be priced under EUR15,000. If the engines were replaced by an AFC, vehicle cost would increase by a factor 3-4! For conventional LDVs, the multiplier would be even higher. Regardless of type, fuel cell cost per kW will have to drop another 90% before it can be considered for mass market applications.
Those, of course, require a fuel infrastructure. Hydrogen is an energy carrier that has to be produced at significant cost. Distribution logistics and on-board storage represent additional daunting problems, not least because of the high pressures (700bar) involved. Special materials such as austenitic steels need to be used to avoid the feared hydrogen embrittling.
Hydrazine is attractive because it is a liquid at room temperature. Handling is still a problem because it is inherently unstable, but the easily reversed adsorption in a polymer matrix to form the stable solid hydrazone is inspired. It means that all of the temporary storage systems in the chain from fuel production facility to the AFC in the vehicle can be made safe at moderate cost. Only aerospace applications require storage of the least stable anhydrous form of hydrazine.
Even so, there are two huge drawbacks. First, hydrazine is highly toxic and also corrosive, so it has to be handled with care during transfer between hydrazone storage systems. In particular, self-service at fuelling stations may not be a feasible option. The underground tanks at the fuelling station must be suitable for the compound to avoid ground water contamination and, regular hydrocarbon tanks don't have much corrosion resistance. Another related issue is vehicle crash safety, though the adsorption into hydrazone should make that much more manageable. Still, fire & rescue crews will need to know that a burst hydrazone tank will release hydrazine if exposed to warm water, such as leaking engine coolant from the other vehicle (assuming that is ICE-powered).
Second - and this is pretty much the death knell - hydrazine is also just an energy carrier. Its production is far more complex and energy-intensive than that of hydrogen, involving ammonia as a feedstock. The Atofina-PUK cycle also involves acetone and hydrogen peroxide.
The well-to-wheels energy balance of a hydrazine-powered AFC is probably no better than that of a diesel-powered car, at fantastically higher cost.
The only good bit of news is that both regular white button mushrooms and false morels contain trace amounts of gyromitrin, which metabolizes to monomethyl hydrazine. IFF this last compound can be used as a substitute for regular hydrazine in an AFC *and* IFF the genetic pathways for gyromitrin production and metabolism can be identified and applied to genetically modified bacteria, it might be possible to produce the required fuel biologically. The energy feedstock would then be whatever the bacteria in question can digest. Perhaps algae could be genetically modified instead, in which case the energy source could even be sunlight. However, bear in mind that this is just wishful thinking on my part, I'm not in a position to assert that AFC fuel really could be produced biologically. In any case, it would still be very expensive.
Chances are, evolving ICE and even PHEV/BEV technology will be cheaper alternatives for many years to come than any fuel cell system and associated fuel production + handling infrastrucutre will ever be.
Posted by: Rafael Seidl | 14 September 2007 at 02:42 PM
I have to agree with the concerns about hydrazine. This is somewhat akin to the use of liquid hydrogen as a potential fuel source. I am relatively open-minded, but I can't see how these researchers aren't rather short-sighted about the practical infrastructure and logistical problems with introducing these types of fuels to the average consumer.
Posted by: Jim Beyer | 14 September 2007 at 04:51 PM
@ Jim Beyer -
liquid hydrogen needs to be distributed and stored cryogenically at 20K, with continuous boil-off. Hydrazine is liquid at room temperature but unstable and highly toxic. Pick your high-tech poison.
Posted by: Rafael Seidl | 14 September 2007 at 04:53 PM
Where does the motivation to persue Hydrogen come from when the alternative, BEVs, are already coming out? Will this somehow propell us through outer space? Batteries and biofuel will be mature long before hydrogen gets halfway to marketable.
Posted by: Elliot | 14 September 2007 at 05:31 PM
Maybe it would be easier to solve the problems of methanol in larger fuel cells. Methanol is not only a good hydrogen carrier but cheap and easy to manufacture from a variety of feedstocks, though vapour barriers would be required. The problem seems to be the membrane from what I understand. Solving the hydrogen carrier problem with hydrazine seems like overkill.
Posted by: Aussie | 14 September 2007 at 05:46 PM
Elliot: International oil companies (IOCs) are very motivated to develop the hydrogen economy because they would maintain their dominant role. Some car companies are in large part owned by oil interests and so, they are putting a lot of effort into hydrogen. In a world of EVs their importance dwindles with demand for liquid fuels. They will certainly deliver biofuels as quickly as they can and some will switch to electricity generation.
Posted by: Neil | 14 September 2007 at 07:47 PM
Rafael: it's my understanding that MMH (which is the fuel in the space shuttle's on-orbit maneuvering rockets, btw) is even more toxic than ordinary hydrazine.
Posted by: Paul Dietz | 14 September 2007 at 09:18 PM
There's a much easier, but not easy answer for fuel cells and cheap fuel. Solid Oxide Fuel Cells and wet ethanol. SOFCs can process a wide range of fuels include ethanol that is 20% water. That reduces the amount of energy necessary to distill the ethanol, because taking out the last 10% of the water requires almost half the distillation energy.
The knock against SOFC's has been that they:
1. run at 600-1,000 degrees celsius
2. require warm up time
3. are bulky
4. are expensive
5. may have durability issues
However, these should all be soluble problems.
1. Aerogel insulation is incredibly effective and compact.
2. Better insulation slows down the rate at which they cool, increases the rate at which they warm up, and when combined with an ultracapcitor and a heating element can preheat rapidly.
3. Packaging of ceramics (tubes, sandwiches, and such)is getting progressively more dense, borrowing lithography techniques from microprocessor industry.
4. ceramics are not inherently expensive materials and are amenable to automation and economies of scale similar to microchips
5. This is a tricky one. They have to heat up and cool down many times, which creates thermal stresses. They have to deal with bumps in the road and deal with kinetic shocks. My hope is that they can just over engineer the ceramics and the shock absorption of the casing.
But if they can get SOFCs to work...we go the same distance on ethanol or butanol that costs 50 cents a gallon.
Posted by: HealthyBreeze | 14 September 2007 at 09:34 PM
The efficiency and power density of DMFCs are not to good.
Wow, very thorough but I don't disagree with a word you said.
Posted by: Ben | 14 September 2007 at 09:46 PM
The solid hydrazone is the intended form for storage and transportation, not the toxic or dangerous anhydrous hydrazine. The solid form will prevent leaching to ground water or into the environment. Hydrazine smells like ammonia, so, eventhough it is miscible in water, contamination will be easily detected, unlike methanol, which is also very toxic but it has little smell or taste. Hydrazine hydrate is less dangerous and has much lower vapor pressure. Transient and short-term use during transfer from one container to another in well-designed mechanism should present low-risk for contamination, given its much lower vapor pressure than gasoline. During a collision, the amount of free hydrazine hydrate inside the FC stack is small and may not present a grave danger.
Even then, Daihatsu admits that much work will be needed, and that they are looking for partners in this research. I just hope that they can find a safer fuel than hydrazine hydrate.
Meanwhile, in order to bypass the expense of PEM FC and difficulty of H2 packaging, and the expense of battery-electric, ICE-HEV directly burning liquid NH3 stored in thin metal tank no larger than current gasoline tank, at pressure of only 8 bars, seems like a more promising way of consuming pollution-free renewable synthetic fuel from renewable energy souces like solar, wind, hydro-electric etc..
Posted by: Roger Pham | 14 September 2007 at 10:18 PM
Thanks Neil, that's what I'd heard, but I figured that perhaps it was just a conspiracy theory and that there was a more enlightened reason. Guess sometimes the smart money's on the cynical. At least with batteries all the chemicals are contained in the battery pack, which should be easily recyclable once the infrastructure starts up. Clean.
Oh well, soon BEV's will be more common, as will efficient PV panels and then pretty soon after the whole power structure will see reform as we'll be less reliant on these companies and their money will go into other things... hopefully things we'll have a choice in buying and that don't pollute.
Posted by: Elliot | 15 September 2007 at 12:51 AM
Hydrazine hydrate is less dangerous and has much lower vapor pressure.
The vapor pressure of hydrazine hydrate at 20 C is 5.2 mm Hg. Hydrazine is considered an immediate hazard to life and health at an inhaled concentration of 80 ppm, and the NIOSH 2hr limit for inhalation is .03 ppm. I do not think hydrazine is detectable by smell at concentrations at which it becomes hazardous.
So, the vapor pressure may be lower, but it's still far far above acceptable limits.
Posted by: Paul Dietz | 15 September 2007 at 01:02 PM
"establishment of the necessary infrastructure"! for hydrazine? Guys lets talk seriously for Daihatsu's sake who clearly are doing good R&D - this can never happen.
If the article had a quote something like "this is an exciting direction for fuel cell research we realise safer fuels must be found but we at Diahatsu have good reason to hope" then OK.
But they have to be told straight out.
Posted by: martin17773 | 15 September 2007 at 05:51 PM
Organic polymer doped with titanium as on-board storage then Aqueous Phase Reforming of glycerol at filling station to provide H2 or ammonia cracking at station with H2 coming from steam electrolysis of geo thermal steam oh and in the far future electrolysis at home to produce H2
Posted by: Mike | 17 September 2007 at 10:48 AM
Posted by: Paul Dietz | 17 September 2007 at 11:09 AM
I think that they can overcome most problems with mobile SOFCs. They are using them for APUs in jet aircraft and the military wants to use them in trucks.
I agree that if you have great insulation (vacuum) you do not have the large cool down over 12/24 hours. This combined with V2G might make them attractive.
The newer copper/ceria designs are very tolerant to fossil fuel impurities and may find their way into mobile applications as well.
Posted by: sjc | 19 September 2007 at 04:33 PM
Brilliand all over...
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Posted by: Leopold Mak Ender | 23 October 2007 at 10:29 AM