Talk:Fuel cell/Archive 1

From Wikipedia, the free encyclopedia

Archive This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

Contents

First image incorrect

Electrons flow in the opposite direction to conventional current. The arrows with e- should be reversed. Could someone please correct this?

-- The direction of the flow is correct -- Electrons flow from the anode side(H2) to the cathode side(O2). The arrows would need to be reversed only if instead of indicating a flow of e-(electrons) it were labeled as i (current), which would flow from cathode to anode. What is incorrect in the image is the (+)label on the anode and the (-)label on the cathode. These two should be reversed. --fiera 19:36, 31 May 2006 (UTC) Done.Mion 02:40, 1 June 2006 (UTC)


-- The direction of flow of electrons is INCORRECT, somebody please change the diagram ---

Electrons flow from the anode(H2) to the cathode(O2) through the external circuit, as correctly stated above. At the anode oxidation of H2 takes place producing electrons and protons, making the anode negative due to excess electrons. Here, as with all electrochemical cells the anode is negative. As opposed to semiconductor or vacuum tube devices with polarity, where the anode is positive. At the cathode O2 is reduced to water by taking electrons from the cathode and protons from the electrolyte, making the cathode electron deficient and therefore positive. As with all electrochemical cells, here the cathode is positive, whereas in semiconductor or vacuum tube devices with polarity the cathode is negative.

When dealing with electrochemical cells (fuel or battery cells), the best way to determine which electrode is the cathode and which one is the anode, is to remember that negative ions, anions are always going towards the anode, and positive ions, cations are always going to the cathode. i.e. anions to anode, cations to cathode.

In the case of the hydrogen fuel cell example, the protons, positive ions, cations are heading to the cathode. They do so because they are diffusing down a concentration gradient, from a high concentration of protons to a low concentration of protons.

So, the only thing that is incorrect in the diagram is that the flow of electrons should be in the opposite direction to that shown, everything else is correct.

Oenus 16:59, 12 June 2006 (UTC)

The protons are not driven by diffusion. The concentration of protons is the same throughout the membrane, and equal to the concentration of negative ions. (Otherwise there would be an unbalanced charge in some parts of the membrane.) It is the electric potential that drives the protons. --PeR 07:26, 14 June 2006 (UTC)

Focus, please.

This article is currently more focused on fuel cell cars than on actual fuel cells. I would like to move a lot of the vehicle-related text to the hydrogen car or similar article, so that this one can focus more on the fuel cell itself.

For the record, I personally don't believe in fuel cell vehicles, but this is not the reason why I want to move the text. It is simply in the wrong place.

--PeR 08:26, 20 February 2006 (UTC)

Doesn't Make much sense

"about 80% of the world's carparks have the legal requirment that cars should be able to start in sub-zero temperatures."

???

Availability of Metals Used in Fuel Cells

Are there any metals used in the construction of a fuel cell for which there is not a large supply, or known reserves of?

Platinum is required for a PEM fuel cell. I think research is being done to try to find another catalyst because platinum is too expensive.

Brianjd

Platinum is not required, it is simply the most effective. They are trying things like Platinum Rubideum mixes which are better in some ways but worse in others - AlexS
To be precise, platinum is not especially expensive in the manifacture of fuel cells; however, if one were to change all internal-combustion engines in the world to fuel cells, there would be not enough platinum in the world (and the price would obviously skyrocket). --Orzetto 20:07, 22 July 2005 (UTC)
The International Platinum Association [1] claims that the supply of Pt should be enough to match the requirement of replacing existing car engines with fuel cells. Current use of Pt in fuel cells is reported at 1.1-1.4 g/kW, with the goal of reducing it to 0.2 g/kW, so that a 50 kW car would use 10 g of Pt, that is about twice what is currently used in the average catalytic converter (4-5 g).
As a person who works in the fuel cell manufaturing field, please note that Pt actually accounts for a very small part of the manufaturing cost. at an average of 5g/m2, using the price of Pt today ($1030/tr oz), we are only talking about $166/m2 of electrode, while base materials run at a much higher price; e.g. Nafion membrane ~$500/m2, Gas diffusion layer ~400/m2, Graphite bipolar plates ~$3000/m2. In comparison, the price of Pt is almost negligible, but definitely something to be worked on.


alternatives to precious metals in fuel cells

I found the biological agent working as a catalyst instead of platinum. It is an enzyme produced by desulfovibrio bacteria. The enzyme is called hydrogenase. More info on subject (or something very near it) here. The article I read it from originally was in Tieteen Kuvalehti, published by Bonnier Publication International. ISSN 0109-2456. The magazine is in Finnish. Khokkanen 00:53, 27 September 2005 (UTC)

"While higher current densities can be achieved in fuel cells using electrodes containing precious metals, the researchers found that good current densities can be generated using a simple carbon anode." -- http://www.spacedaily.com/news/energy-tech-04zzg.html

Precious metals are needed for low temperature activation of hydrogen and oxygen molecules, as catalysts. For a reaction to occur, chemical bonds need to be broken, either by temperature or by catalysts. Platinum that dissolves hydrogen can break hydrogen and oxygen into reactive atomic species. In absence of catalysts you can use high temperatures - 500-1000 °C, and then you can use any kind of electrode, carbon, copper, anything that conducts electricity, you don't need a catalyst-electrode. Sillybilly 04:00, 27 December 2005 (UTC)
In my experience, you can use plain carbon electrodes in PEMFCs and AFCs with little or no degradation in power, but electrode life is cut by about a factor of ten: instead of a few thousand hours of operation, you will only get a couple of hundred. -- Thopper 04:48, 8 January 2006 (UTC)

More generally, others on this site have pointed out that palladium and rhodium have been used with success in PEM. I have also seen some work with cobalt porphyrins, but the cobalt doesn't stand up well in the acidic environment of the membrane, even when encapsulated in the porphyrin molecule. AFCs, of course, do not have this problem, and operate quite happily with non-noble metals as catalysts. Nickel anodes and silver cathodes have been used for decades in terrestrial AFCs, cobalt porphyrin is quite stable, and other catalysts have been tested. -- Thopper 04:48, 8 January 2006 (UTC)

I'd be interested in a specific PEM example that uses only pure plain carbon electrodes that are non-platinized, palladized, etc. Usually the precious metals and catalysts are carried on a conductive but inert support material, which may happen to be carbon, but the key is not the support material, but the catalyst it supports. You can probably get away with using carbon or any kind of electrodes on the oxygen side of PEMFC's, as long as you do use catalysts at least on the other side, providing low activation energy on the hydrogen side, that generate the hyperactive atomic hydrogen/proton that's capable of reacting with unbroken, still molecularly intact oxygen. It's what's called a free radical chain: H* + O2 -> HO* + O*, HO*+H*->H2O, O*+H*->OH*, O*+O*->O2, the * signifying hyperactive, high energy state free radicals or atomic species. Only O2 and H2O are stable, and nonreactive, the rest are restless, they rummage around until they find something quench themselves with into a nonhyperactive, stable state. But any free radical chain reaction needs to be initiated somehow, either by heat, light, or catalysts, and PEMFC's being low temperature and and non-UV-irradiated but dark, they need catalysts at least on one side. Of course besides platinum, there are other metals capable of functioning as catalysts to a lesser degree, including almost all the precious metals such as palladium, rhodium, ruthenium, iridium, osmium, that are all very expensive, or even less expensive [[Rai]ney nickel]] that's used in vegetable oil hydrogenation to produce margarine, or nickel-titanium-vanadium-rare-earth based electrodes such as used in NiMH batteries (by the way NiMH batteries could use platinum too, they'd just be too expensive that way), or sophisticated organometallic compounds such as the cobalt compounds you mention. Life deals with molecular oxygen via hemoglobin, that contains heme, an iron centered organometallic compound, and the hydrogenase enzyme Khokkanen mentioned is iron-nickel-sulfur based. Life uses different catalysts than precious metals for all the internal dealings, for all the enzymes, because it cannot deal with platinum that's so unreactive when it comes to forming compounds that can be carried in a bloodstream. The point here is that at low temperatures there is a need for catalytic action and not just anything will do, but yes, there are different catalysts with different catalytic capabilities, and different stability/longevity issues, and platinum may not be the one that wins out in the long run, but for now it's one of the longest life materials due to being so inert/nonreactive/stable - it cleans itself of any tarnish because it prefers being in the unrusted metal state, so platinum rust/crud will jump back to shiny platinum metal at the slightest chance, while it's superhigh reactive when it comes to catalytic action of forming atomic species on its shiny/black surface. AFC's using a bit higher temperature can probably get away with weaker catalysts. Temperatures above 5-600°C don't need any catalysts, or room temperature systems that are UV irradiated also don't need catalysts, but you need some way to deal with the activation energy. Life uses enzymes, but enzymes aren't forever either, they degenerate and age, and they have to keep being replenished by life on a daily basis. What's cheaper, more effective? Keep replacing the aged electrodes in a fuel cell every hundred hours, or buy a very expensive platinized electrode that needs to be replaced only after a few thousand hours? Sillybilly 09:02, 8 January 2006 (UTC)
I should have been somewhat clearer: you can use plain carbon, but it is not desirable for the reasons you have so nicely summarized: the free radicals which attack the carbon and degrade the electrodes, leading to short life. I cannot think of any specific print references to this (other than the SpaceDaily news item previously referenced), but if I can find one, I'll pass it along. I certainly wouldn't expect anyone to try this for any real-world application. I have tried it myself with AFCs as a baseline for other investigations, and spoken to a few researchers who have done the same with PEMs. Most of this work was probably done between 40°C and 100°C. I'm not sure what would happen at lower temperatures; perhaps the catalyst would contribute more to higher powers. Under normal operating conditions, it's the high surface area carbon used in the electrocatalyst layer that supports the high current density, while the catalyst largely seems to prevent attack on the carbon (and, of course, boosts power slightly).
My point, though, was not to suggest that noble metals are not needed, especially in PEM, but to contribute to the discussion of "alternatives to precious metals." You can use others, but nothing works as well as platinum and some combinations of platinum with a few other noble metals, especially in PEM, as you have said. In AFCs using flowing electrolyte (and hence a relatively high ohmic impedance), though, DSK-style Raney Nickel anodes seem to work as well as Pt-carbon anodes, and at slightly lower cost. Incidentally, I have worked with metal hydrides containing small percentages of platinum (less than one percent), and the improvement in performance is substantial. Too bad Pt is so darned expensive. -- Thopper 14:55, 8 January 2006 (UTC)
I went and read that SpaceDaily article more in depth, and the gist of it is that they use polyoxometalate catalysts, that look something similar to what life would be using, it looks like electrolyte dissolved salts that could be carried in a bloodstream, or as nondissolved salts supported on the membrane/electrode. These catalysts function as oxygen activators, even atmospheric molecular oxygen, so in a fuel cell you'd have something roughly along the lines of O2->2O* (activation step, it's probably not this simple), O*+H2O->2 HO*, e-+HO*->HO-, high energy hydroxyl ions generated at the oxygen electrode, which wander over through the electrolyte to the hydrogen side and attack the otherwise inert molecular hydrogen H2 + HO*->H*+H2O, etc, if that works like that, without activation. That they can catalyze and activate atmospheric oxygen is a big deal, but you may still need hydrogen side activation too - they say "carbon anodes," what about the cathodes? They still need platinum fro cathodes? Usually PEMFC's use platinum to do the hydrogen activation, where platinum excels, but they also use platinum for oxygen activation too. They would probably have to look into coupling polyoxometalate for oxygen side reactions with the secrets stolen from life's above mentioned hydrogenase enzyme working on the hydrogen side, to completely eliminate precious metals for both electrodes, because platinum works on both sides as a catalyst/activator. Or you may just use polyoxometallates on the oxygen side, and titanium-nickel based NIMH battery electrodes on the hydrogen side.
One of the issues is that most polyoxometalate catalysis research is into selectivity, into incomplete oxidation[2] [3], when in case of a fuel cell you'd like full and complete oxydation of anything that gets thrown at it on the cathode side, be it molecular hydrogen that needs a hydrogenase catalyst to get activated, or methanol, wet undistilled(therefore cheap) ethanol, glucose, etc. In the latter cases you'd have to deal with figuring out how to catalyze the oxidation reactions all the way to CO2, then how to carry the carbon dioxide buildup away, just like life running on glucose does. Life figured it all out at room temperature, how to harness the chemical energy stored in glucose + atmospheric oxygen, why can't we make a good fuel cell doing the same thing, at room temperature? One of the issues with life is speed of reactions, power generation capacity because of the low temperatures - there can be sudden instantaneous loads, but sustainable levels of energy loads are relatively low - people get tired because of concentration buildup, reactions only happen so fast at low temperatures, more fuel and oxygen needs to diffuse to the reaction site that only diffuses so fast, and life can only work so hard for extended periods and not much harder, it gets tired. This might be an issue when we try to copy life, fuel cells would get tired, i.e. overloaded, but it's scalable, elephants are equivalent to some pretty heavy duty machinery, so there is a good outlook there, though hopefully a fuel cell based on life-like catalysis of equal power to an elephant, would be much smaller size than an elephant. Sillybilly 18:10, 8 January 2006 (UTC)
One idea here is just to use life on the cathode side - aerobic bacteria that are starved for oxygen and use up any amount they can find to process the sugarcane solution they are floating in. This would set up an oxygen concentration differential across a membrane driving an electric current, just like concentration-batteries do. Basically you'd have the polyoxometalate catalyze atmospheric absorption to convert O*+H2O+2e-->2 OH-, sucking electrons providing you with a positive electrode, then on the other side of the electrolyte-membrane the process reverses to 2OH-->O*+H2O+2e-, and the O* would be in a form that the bacteria could process. There are probably different kind of bacterias that can live under various kinds of oxygen starvations and still do fine, but I don't know ultimately what kind of efficiency you could derive from such a system, because life itself isn't that efficient in converting chemical energy, some always gets wasted at each step, in each reaction, and then there is a lot of energy needed to maintain order, decreased entropy, for life to function at all. There is also the ethical issue of "bacteria starvation" that animal rights, or bacteria rights activists might stand up against. Sillybilly 09:19, 9 January 2006 (UTC)
By the way, sugar, which is easily carried in a solid form, and unlike coal or aluminum, it's easily soluble in water to be available to catalysts, has an energy density of 17 MJ/kg, compared to 13 for aluminum and 23 for coal, as shown at the pumped storage article. Life was pretty good at coming up with an energy dense, water soluble, and easy to handle energy storage medium. The hard part, of course, is the low 0.03% concentration atmospheric CO2 extraction that we might have a hard time to efficiently duplicate in conjunction with solar panels, and still beat the 0.5-2% overall efficiency of photosynthesis with our 15% efficient solar panels. We may find it easier to just process sand or aluminum minerals instead, or even water into hydrogen/liquid ammonia, which are much more concentrated and plentiful on the planet with high turnovers unlike biomass which can only recover so fast after a harvest. Another idea is to use fuel cells and instead of releasing CO2 into the atmosphere where it dilutes away, we could capture it, either in a liquid CO2 state, or some chemical state, and ship it to the solar processing station to be "recharged." Sillybilly 11:24, 16 January 2006 (UTC)

Fuel cell as Battery

I think this section is unnecessary now. I will read through it properly when I get the time.

Brianjd 12:26, Nov 5, 2004 (UTC)

I have archived the old talk in Talk:Fuel cell/Battery? and summarised it below. Note that all the blockquotes are actually quotes. Brianjd 10:14, 2004 Nov 16 (UTC)

Jerzy argues that a fuel cell *is* a battery and not merely *like* a battery, that therefore all battery laws also apply to fuel cells, and that even if this is wrong, a clear explanation of the difference should be given.

Mkweise argues that a battery is an ESD (energy storage device) and a fuel cell as an ECD (energy conversion device).

Jerzy says that the lead-acid automotive battery and the pumped storage plant are both ECDs, agrees that a fuel cell "cannot be reasonably construed as an ESD" and provides the following thought experiment:

But a better approach is to think about a system with a primary battery that is is not storing energy, but only converting it from chemical to electrical form. It's tempting to say that just disconnecting the charging system doesn't change the function of the disconnected at any given moment, and periodically they change roles. You, or your robot battery restorer, is at work on the disconnected battery: the depleted electrolyte gets dumped in the road and replaced from your sulphuric acid tank, while the sulphated electrodes get pulled out and stuffed in the trunk (for trade in), and fresh lead-metal electrodes, delivered like belted machine-gun ammunition, get installed in their place, so that battery is rebuilt and ready to take its turn as active battery. The tank and electrode magazine are storing energy as the fuel-cell tank does, but the electrolyte and electrodes in the lead-acid ECD have an energy storage function no more than is does the fuel in the space between the electrodes of the fuel cell; this kind of storage is merely incidental to the ECD process. Thus i think we have an "open ended", ESD-free, lead-acid battery ECD.

(I haven't checked the battery (electricity) article to be sure whether you've been misinformed by it or misinterpreted it; if you want to point out specifics, i'd be willing to express an opinion as to which applies.)

Jerzy believes that the same physical laws apply to both batteries and fuel cells:

(We're not, for instance, talking about cold fusion here; if new principles in chemistry had been involved, i'm confident i'd have heard about that.)

Mkweise:

From the viewpoint of pure physics (which you seem to be taking), batteries and fuel cells would both be referred to as electrochemical cells. They are fundamentally the same, just as motors and generators are - but from a functional viewpoint they are completely different: One is a closed system that holds an exhaustible supply of energy, while the other depends on a continuous external fuel supply. Think of a syringe vs. an IV line. Or, to use your own analogy: you wouldn't think of saying that a blast furnace is a type of forge (or that a forge is a type of blast furnace)—would you? And yes, all ESDs except capacitors internally employ two-way energy conversion but that, again, is beside the point as these are also functionally (as opposed to fundamentally) defined terms.

Hankwang believes that the definition of a battery is too vague to resolve this debate and suggests:

So, choose either "a kind of battery" or "similar to a battery" in the description of a fuel cell. In both cases, describe the important features that distinguish a fuel cell from what is commonly called a battery, mainly the fact that the latter normally is a chemically closed system. But then, a zinc-air battery for hearing aids isn't closed either.

Summary of a post signed "bblakemo@ford.com 8/10/2004":

Unlike capacitors, complex and multiple chemical reactions happen in batteries so they are difficult to model, and they are really ECDs (energy conversion devices, as opposed to ESDs - energy storage devices). Also, in a hydrogen-oxygen fuel cell, hydrogen should be called the anode and oxygen should be called the cathode (rather than the membrane and catalyst being called the cathode and anode). "I understand that this is a somewhat simplified view that does offer some problems in practice but would ask the reader to consider the Nickel Hydrogen battery in which gaseous Hygrogen is truely considered the Anode."

First hydrogen station

The article states (in a US-centric view maybe) that the first public H2 station was opened in Washington, DC, in november 2004. I was in Reykjavik in november 2003 and I visited the local H2 station. Maybe it boils down to the word "public". What is meant by that? If it is providing only for 6 state-owned vehicles, it's less public than Reykjavik's, which supplies a couple of hydrogen buses (which are regularly used by the public, bus route number 2 I think). See this link. Orzetto 12:06, 10 Dec 2004 (UTC)

...Since no objections are raised, I'll substitute in the Reykjavik station instead of the Washington one.Orzetto 09:06, 14 Dec 2004 (UTC)

Breakthrough in fuel-cell technology (in german sadly)

If someone here is interested in the subject and speaks some german you can find in interesting article about a new form of fuel cell developed by the Fraunhofer Institute in Germany here: http://www.n-tv.de/5465399.html Cheers, --Jpkoester1 11:25, Dec 21, 2004 (UTC)

I'm a hydrogen reasearcher, I can tell you that people keep inventing new types of fuel cells all the time. There are many ways to build a cell, and the link you posted tells of a "secret composition", that by the public may sound like "very advanced", but to mine sounds like "vaporware". Unless something about this is found in peer-reviewed journals, this is not to be taken too seriously. --Orzetto 21:02, 22 July 2005 (UTC)

Not a relevant argument anyway

I always used to think this is a good reason against hydrogen economy until i came across the post i have linked at the end this talk. "The hydrogen typically used as a fuel is not a primary source of energy: it is only an energy carrier, and must be manufactured using energy from other sources. Some critics of the current stages of this technology argue that the energy needed to create the fuel in the first place may reduce the ultimate energy efficiency of the system to below that of the most efficient gasoline internal-combustion engines; this is especially true if the hydrogen has to be compressed to high pressures, as it does in automobile applications (the electrolysis of water is itself a fairly efficient process)." This is from the main page. The main argument is hydrogen is not a source of energy, but what the argument avoids to say is gasoline is not a source of energy also. Once you agree with the fact that gasoline(Also a store of energy) is not a source of energy, the above argument becomes mute. This post nicely summarize the whole argument. [4] Note, even if you don't believe the above, hydrogen would still be a better option in that it would allow centralization of the gasoline usage. This would mean easy control of emission. In short, that argument is hopelessly weak

Gasoline is not a store of energy because it doesn't take more energy to produce it than you get from burning it. If we didn't have energy sources, instead of stores of energy, we'd be violating the laws of thermodynamics. If hydrogen gas was available in the environment, it could be used as an energy source, but it isn't. -- Kjkolb 13:44, 2 January 2006 (UTC)
Neither does hydrogen. If you produce hydrogen from natural gas, the first reaction is (I lump together the reforming and water shift reactions, forgive me; data from NIST):
CH_4+2H_2O \rightarrow 4H_2 + CO_2, which has a ΔG = 113.13kJ / mol at standard conditions;
Then we burn hydrogen and we get:
4 H_2 + 2 O_2 \rightarrow 4 H_2O, with a ΔG = − 912.25kJ / mol at standard conditions.
The result is that we use 28.2 kJ to produce a mole of hydrogen, that returns us about 228 kJ when we burn it.
In fact, there are indeed ways to produce gasoline that could require more energy that what you get. When Nazi Germany was out of fuel, they used the Fischer-Tropsch process to make fuel from coal. Given the efficiencies of the time, it is quite possible they used more energy in producing the fuel than what they got out of it in mechanical work. --Orzetto 16:24, 19 February 2006 (UTC)
The fact that it is not an energy source should not be taken as an argument against using hydrogen. It's just something that you should take into consideration. Many people talk about using hydrogen, but they are not aware of where it comes from. We can produce it from fossil fuels or using renewable energy, but it is not a source of energy. -- Kjkolb 13:47, 2 January 2006 (UTC)
Well, gasoline can be considered an energy carrier, it's carrying all that solar energy collected in the past. Hydrogen is a very efficient energy carrier, giving it future potential, especially when fossil fuels that have carried so much solar energy from the past, have run out. PeregrineAY 20:18, 2 January 2006 (UTC)
It depends on your definition of an energy carrier, and I was using one that defined them as fuels that take more energy to produce them than we get from burning them. Even with all of the work to find, transport and process oil, we still get more energy than we put into it. The same with nuclear, hydroelectricity and solar. Batteries, hydrogen and electricity are energy carriers under this definition. Hydrogen production requires other energy sources such as solar, nuclear or coal. It should not be viewed as a put down on hydrogen. It takes more energy to produce electricity than we get out of it, but we produce it anyway because it is a high value form of energy. The same might be true of hydrogen when there is widescale production. People need to understand that it's not an energy source because they often speak of hydrogen as if it were, like suggesting the conversion of all power plants and vehicles to hydrogen. They should also realize that whether using hydrogen reduces pollution depends on how it is made. -- Kjkolb 15:14, 7 January 2006 (UTC)
I hope you'll pardon me jumping into the conversation. The formulation that I believe I have seen more frequently is to refer to fossil fuels as hydrogen carriers, and make a distinction between primary and secondary energy sources. In this formulation, oil is a hydrogen carrier and a primary energy source. Batteries, compressed hydrogen tanks, or metal hydride would all be considered secondary energy sources. I have rarely seen "energy carrier" used in the literature. After all, from a fundamental perspective, everything is an "energy carrier." -- Thopper 23:11, 7 January 2006 (UTC)


Agree with Thopper, everything is an energy carrier. But, when we argue for or against hydrogen economy, whether H2 is a source of energy or a mere carrier is something completely irrelevant. Fuel cells are compared, and often opposed, to internal combustion engines, or should I say, H2 is opposed to gasoline, not because they are a source or a carrier, but because of the result of an equation that balances "cleanliness", efficiency and renewability (and other factors). Of course it would not make much sense if we were to burn gasoline to generate electricity, to then make H2 by electrolysis, but if the electricity came from i.e. solar power, we can then generate H2; therefore greatly justified, and definitely not inefficient, regardless of the high pressure storage or etc.--fiera 17:54, 31 May 2006 (UTC)