Cleaner Hydrogen Generation

Astro14

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Makes no difference. Clearly, the author has no scientific understanding. Stating that this is cleaner is also false. The energy required to split H2O into its component elements (known as hydrolysis) remains the same for every molecule split. Scale doesn't change efficiency. It takes a lot of energy to liberate the hydrogen. This device simply uses a different catalyst, but that doesn't change the energy required. The author ignores the energy source throughout the article and gets the energy source wrong in the steam reformation do natural gas (the natural gas is being split up...it's not a global warming contributor...however, the energy required to run the process has to come from somewhere). Sadly, a working knowledge of thermodynamics did not inform the opinions in the article. So, if you do it with a little battery, you'll get a little hydrogen. Ironically, you'll get more electricity from the little battery than you will from running a fuel cell on the little bit of hydrogen created by this science project because of the imperfect efficiency of hydrogen creation and of the fuel cell... So, they have cleverly turned the little bit of electricity in the battery into an even smaller amount of electricity by using two very expensive bits of technology....their new device and a fuel cell... At best, a small step backwards!
 
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Y_K

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There is never a free lunch with Energy. That's what I alluded to in my initial post. And fuel cells are among the worst offenders. Yet as an element of a patchwork, this could be a nice band aid for the wind/solar/clean/etc. We can't build giant storage batteries, but splitting water gives us the ability to store vast quantities of readily available energy, and the low voltage dissociation is a good step methinks.
 
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Originally Posted By: Astro14
So, they have cleverly turned the little bit of electricity in the battery into an even smaller amount of electricity by using two very expensive bits of technology....their new device and a fuel cell... At best, a small step backwards!
The same thinking as using an electric motor to spin a generator to power the motor. The losses are there so it won't work. Expending more energy than you get out of it makes no sense.
 

Astro14

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Originally Posted By: Y_K
There is never a free lunch with Energy. That's what I alluded to in my initial post. And fuel cells are among the worst offenders. Yet as an element of a patchwork, this could be a nice band aid for the wind/solar/clean/etc. We can't build giant storage batteries, but splitting water gives us the ability to store vast quantities of readily available energy, and the low voltage dissociation is a good step methinks.
I missed that in your original post. I apologize. You make a reasonable point about the low voltage/small scale hydrolysis having potential applications for storing large amounts of energy that was generated on a small scale. Certainly those off the grid would appreciate that ability...
 

Y_K

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No worries at all. It is just another small step out of many. There are some great breakthroughs with nano and phenom as well, as there are many others. in fact, energy density of some cutting edge batteries is so high that gracious release is the real challenge. I agree that the sensational journalism penetrates everywhere, by its very nature it is superficial, of course.
 

JHZR2

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Originally Posted By: Y_K
There is never a free lunch with Energy. That's what I alluded to in my initial post. And fuel cells are among the worst offenders. Yet as an element of a patchwork, this could be a nice band aid for the wind/solar/clean/etc. We can't build giant storage batteries, but splitting water gives us the ability to store vast quantities of readily available energy, and the low voltage dissociation is a good step methinks.
Fuel cells are not worse than most. Compared to diesel and gas turbine generators, their efficiency is higher, due to not being restricted by Carnot as a heat engine. Yes, the numbers shown in a theoretical fuel cell are high and not obtainable, but higher than diesels is doable. I have personally run reformer-based systems at hundreds of kilowatts that achieve >50% thermal efficiency in terms of LHV of fuel in (F-76 diesel and. JP-5 jet fuel, so the losses of desulfurization are factored in). Stored hydrogen is a bad offender, because of the means of producing it and storing it. But steam and auto thermal reformation with the appropriate shift reactions can be a very efficient means of producing hydrogen, assuming you consume it as you make it. Electrolysis, even sofc-based high temperature electrolysis (compared to standard Pt/Ir PEM electrolyzers) is pretty inefficient.
 

JHZR2

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Originally Posted By: Astro14
Makes no difference. Clearly, the author has no scientific understanding. Stating that this is cleaner is also false. The energy required to split H2O into its component elements (known as hydrolysis) remains the same for every molecule split. Scale doesn't change efficiency. It takes a lot of energy to liberate the hydrogen. This device simply uses a different catalyst, but that doesn't change the energy required. The author ignores the energy source throughout the article and gets the energy source wrong in the steam reformation do natural gas (the natural gas is being split up...it's not a global warming contributor...however, the energy required to run the process has to come from somewhere). Sadly, a working knowledge of thermodynamics did not inform the opinions in the article. So, if you do it with a little battery, you'll get a little hydrogen. Ironically, you'll get more electricity from the little battery than you will from running a fuel cell on the little bit of hydrogen created by this science project because of the imperfect efficiency of hydrogen creation and of the fuel cell... So, they have cleverly turned the little bit of electricity in the battery into an even smaller amount of electricity by using two very expensive bits of technology....their new device and a fuel cell... At best, a small step backwards!
You're missing the point. Catalysis is indeed a means of reducing the activation energy of a chemical reaction. If you look at chemical activity and Gibbs free energy, and calculate based upon Nernst, you get somewhere around 1.2v as the standard potential of water electrolysis. Phase changes and thermal issues (losses and other enthalpic effects) makes it more like 1.5v, and the usually some additional overpotential is applied. Doing this via a proton shuttle (PEM) vs an oxygen shuttle (hi-temp SOFC) can have efficiency differences. Yes, a mole of water requires two moles of electrons to split. That is what it is. And recall that a coulomb is around 10^18 electrons (so not quite a mole) and that it is also an A*s. So an ampere is really depictable in terms of moles of electrons. So for a mole of water, the amperes required will not change from a number of atoms or number of electrons basis, but the potential that the electrolysis can occur at, or more specifically, the overpotential (waste) required, can be reduced with appropriate catalysis. So what happens is that for a given number of moles, at a lower overpotential, a lower total number of watts are required, since V*A=W. Then if you apply an effective flow rate and time based term in there, what you ultimately can get is Wh/quantity of H2, all going back to fewer watts because fewer volts, because of better catalysis of the electrolysis, and cheaper to boot. So there is an effective energy savings due to reduction of overpotential, which is really all that is being stated. Specifically, "The nickel/nickel-oxide catalyst significantly lowers the voltage required to split water, which could eventually save hydrogen producers billions of dollars in electricity costs". The cost aspect is not only in electricity, but also in precious metals acquisition cost. Nafion isn't cheap either. If you make a polarization curve for a PEM fuel cell, there are distinct regions. They are activation losses, oh if losses, and mass transport losses. Catalysis reduces the activation losses, and superior designs can reduce ohmic losses as well. That can be a non-trivial amount of overpotential that is removed.
 
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We lose 260,000 kg of Hydrogen a day by atmospheric escape. Unless we get a bunch of ice balls to hit us we will eventually lose our water resources. Speeding up the process is Lunacy (splitting H2O). Im sure some space dust in the form of H20 settles in but I highly doubt its to that magnitude.
 
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Originally Posted By: Koz1
Speeding up the process is Lunacy (splitting H2O).
The reverse happens when using hydrogen to "obtain" energy. I wouldn't worry about losing water to space for several lifetimes. We have enough water issues of our own design with which to concern ourselves first.
 
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Luck that burning a pound of gas makes a fair bit more than a pound of water vapour. I'd be (personally) more worried about running out of oxygen...and I'm not very worried about that.
 
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Hydrogen from electrolysis and then use the generated hydrogen for fuel cell makes it a very inefficient battery, at least in terms of cost. It may be useful if you need reduced weight (i.e. hydrogen fuel cell airplane), but many other sources would be much cheaper (pumping water back up a dam) and much more efficient (chemical battery). To make hydrogen fuel efficient, you have to use power plant to generate the hydrogen AND at off peak hours when the heat source would have been wasted (i.e. you don't have any smelter or aluminum refinery anywhere nearby to use the electricity). To make SOFC efficient, you have to find way to use and reclaim those waste heat from the exhaust for something else (i.e. industrial process). What's the point of running natural gas into a 50% efficient fuel cell when a combined cycle natural gas plant is near 60% these days?
 

JHZR2

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Because a true recuperated, combined cycle gt-FC plant is even higher. No Carnot, far less air so far fewer pumping losses. I've run >50% fuel cell plants (LHV basis) running off liquid fuels. Go to methane, internally reform and shift (co+h2o yields free hydrogen) and then any additional waste heat and energy content of anode tail gas goes into a gt, which also serves as a transient buffer. GE LM6000 is already 42% thermal efficiency...
 
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So what you are saying is: if you can run a fuel cell at 50%, and then turbine for the remaining exhaust at 42% efficiency, and then use the remaining heat to boil water, you will get something like this in maximum efficiency: 50% + 50% * 42% + 50% * 58% * (whatever steam generator efficiency is at) = 71% + 29% * whatever steam generator efficiency is at
 

JHZR2

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Something like that. The only true measurement is kWe out per LHV of fuel put in. I'll write more later.
 
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Agreed..."heat rate" is where all of this stuff should be, useful energy obtained divided by energy input. Can then invert it and call it "efficiency"
 
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