Temporary storage for electrons: Natural method of producing hydrogen

Nov 02, 2012 by Dr. Rebekka Loschen

Scientists at the Max Planck Institute for Chemical Energy Conversion (MPI CEC) and the Ruhr-Universität Bochum (RUB) have found through spectroscopic investigations on a hydrogen-producing enzyme that the environment of the catalytic site acts as an electron reservoir in the enzyme. Thus, it can very efficiently produce hydrogen, which has great potential as a renewable energy source.

The research team describes their results in the journal .

The system analysed constitutes an enzyme that catalyses the formation and conversion of hydrogen. In its centre it has a double-, and is therefore also called [FeFe] hydrogenase. Hydrogenases are of great interest for energy research, since they can efficiently produce hydrogen. However, new catalysts can only be developed given a deep understanding of their mode of action.

In hydrogen production, two electrons get together with two protons. The research team showed that, as expected, the first electron is initially transferred to the iron centre of the enzyme. The second transfer on the other hand is to an iron-sulphur cluster that is located in the periphery. It thus forms a temporary storage for the second electron. This "super-reduced" state may be responsible for the extremely of the hydrogenase. Subsequently both electrons are transferred in one step from the enzyme to the protons, so that hydrogen is generated. "Only the use of two different made the discovery possible", says Agnieszka Adamska, a doctoral student at MPI CEC who carried out the spectroscopic studies.

"Up to 10,000 molecules of hydrogen per second can be generated by a single [FeFe] centre", says Camilla Lambertz, a postdoc at the RUB who prepared the for the project. The enzyme is thus among the most efficient hydrogenases and is therefore also being intensively investigated by biologists and chemists with a view to achieving environmentally friendly . The complete mechanism of hydrogen formation is, however, complex and several steps need to be clarified. Next, the researchers at MPI CEC and the Ruhr-Universität Bochum aim to use sensitive spectroscopic methods to locate the proton to which the two electrons are transferred. This negatively charged hydrogen atom (hydride) reacts with another proton to form hydrogen. Inspired by the [FeFe] hydrogenase, the researchers would like to develop their own hydrogen-producing catalysts that could be used for the generation of hydrogen.

Explore further: The fluorescent fingerprint of plastics

More information: A. Adamska, A. Silakov, C. Lambertz, O. Rüdiger, T. Happe, E. Reijerse, W. Lubitz (2012): Identification and Characterization of the "Super-Reduced" State of the H-Cluster in [FeFe] Hydrogenase: A New Building Block for the Catalytic Cycle?, Angewandte Chemie International Edition, doi: 10.1002/anie.201204800

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Sanescience
3.3 / 5 (6) Nov 02, 2012
"hydrogen, which has great potential as a renewable energy source."

The sun fusing hydrogen is an "energy source." Hydrogen produced from energy here on Earth is an "energy carrier."

As an energy carrier, molecular hydrogen is very inefficient and unnatural. Systems that use it or store it involve expensive equipment that tends to be heavy (high pressure systems) and itself power hungry (cryogenics).

Nature's solution to the hydrogen "dilemma" are the hydrocarbons that dominate natural processes. Once renewable carbon neutral hydrocarbon production ramps up, hydrogen will be unable to compete and will fall by the way side.
antialias_physorg
3.5 / 5 (2) Nov 02, 2012
The sun fusing hydrogen is an "energy source."

Maybe you missed the 'renewebale' part?

By your logic oil, wind, coal, (and even nuclear) wouldn't be an energy source, either.

As an energy carrier, molecular hydrogen is very inefficient and unnatural.

On the contrary. Hydrogen is the most 'natural' thing there is.

Systems that use it or store it involve expensive equipment that tends to be heavy (high pressure systems) and itself power hungry (cryogenics).

You should read a bit here on physorg. About stuff like metal hydrides and similar. Whether a system is heavy is alos very irrelevant for a local storage unit. That only comes into play if you use it for cars.

hydrogen will be unable to compete and will fall by the way side.

Hydrogen has the adcantage of nor producing any pollutants when 'burned'. Especially for cities that is a very decisive issue. So I wouldn't discount hydrogen just yet if you include 'quality of life' in your calculations.
Sanescience
1 / 5 (1) Nov 02, 2012
By your logic oil, wind, coal, (and even nuclear) wouldn't be an energy source, either.

One example of an energy source does not exclude all others. However time scale is an important factor in the philosophy of energy sources. As far as we know fossil fuels are really the storage of solar energy over geological time. So on a human time scale it is regarded as a "source" of energy, but we recognize that it is non-renewable because its rate of replenishment does not match our time scale.

Saying wind and hydro is really solar energy because the sun drives weather patterns is probably omitted from discussions because in is an unnecessary "over complicating" for most people to discuss.

Nuclear is really two things. The fission of heavy atomic nuclei is kind of a middle ground. The quantity of energy theoretically obtainable from it makes it "nearly" inexhaustible. A reasonably efficient version of fusing light nuclei however would qualify for practically inexhaustible.
Sanescience
1 / 5 (1) Nov 02, 2012
As an energy carrier, molecular hydrogen is very inefficient and unnatural.

On the contrary. Hydrogen is the most 'natural' thing there is.

You are subtly changing my statement. Molecular hydrogen is not "hydrogen". Molecular hydrogen, or the chemical H2, a gas at most temperatures and pressures, does not concentrate naturally in any significant quantities. If released into the air, what doesn't oxidize as it quickly rises due to its unrivaled buoyancy ends up being stripped from the high atmosphere into space by the solar winds.
Sanescience
1 / 5 (1) Nov 02, 2012
Systems that use it or store it involve expensive equipment that tends to be heavy (high pressure systems) and itself power hungry (cryogenics).
You should read a bit here on physorg. About stuff like metal hydrides and similar. Whether a system is heavy is alos very irrelevant for a local storage unit. That only comes into play if you use it for cars.


My statement of "as an energy carrier" is separate from "energy storage" though many disadvantages are shared in common. For example a large molecular hydrogen storage system is complex compared to a tank of diesel.

Harryrob
not rated yet Nov 02, 2012
Guys the solar radiation consist of protons and electrons right?
But then can we recombine these to make hydrogen in space?
can be used as a fuel in space and can also be used for making water?
Jeddy_Mctedder
1 / 5 (3) Nov 02, 2012
everything is an energy carrier from the big bang if you want to get right down to it. stop with that bullshit though, hydrogen is not so much an energy carrier as it is the medium of the processes which are hoped can efficiently harness the sun directly through solar power, or through the offshoot heat from industrial processes or even from nuclear power plants itself.

a lot of the big hype about hydrogen has been waste heat. waste heat is a big issue and probably the low hanging fruit inso far as new technology being concerned. harnessing waste heat from industrial processes and from power generation is a major big open door that needs to be walked through. that heat must be stored in a battery , chemical form, or is mechanical potential energy (compressed, accelerated or gravitationally pumped matter) . waste heat storage = big gains.
RealScience
not rated yet Nov 02, 2012
SaneScience - yes, nature has figured out how to store hydrogen - attach it to carbon chains. But nature also can throw an oxygen into the chain (alcohols), or multiple oxygens (sugars and starches).

AP: Your point about hydrocarbons polluting applies if the hydrocarbons are burnt. But direct methanol and direct ethanol fuel cells are becoming practical, and someone will figure out a direct hydrocarbon fuel cell at some point. If we then get the carbon and the hydrogen from water using solar energy we get the best of both worlds.
Sanescience
not rated yet Nov 03, 2012
Guys the solar radiation consist of protons and electrons right?
But then can we recombine these to make hydrogen in space?
can be used as a fuel in space and can also be used for making water?

Yes, those are the main components of the Solar Wind. Solar radiation tends to refer to the light, or electromagnetic radiation (sunlight) given off.

However to make molecular hydrogen, the winds density is very low and would not be practical. And to make water you would need to carry your own supply of oxygen.
antialias_physorg
not rated yet Nov 03, 2012
But then can we recombine these to make hydrogen in space? can be used as a fuel in space and can also be used for making water?

Sorta. The water on the Moon is probably formed that way.
http://en.wikiped...oduction

But consider that very little has formed and that that has been going on for billions of years. So it's probably not a method that works on any scale that is useful to spacecraft.

But direct methanol and direct ethanol fuel cells are becoming practical

That would be an option. The CO2 concentration in the cities would still be as high as it is now (those fuel cells do produce CO2 which is imported from 'elsewhere'). From an engineering standpoint the hydrogen fuel cell cycle is just simpler.

Hydrogen is also not really useful as a fuel in space (by itself) unless you use it for fusion. For hydrogen to be useful in fuel cells you still need oxygen.
RealScience
not rated yet Nov 04, 2012
AP - fuel cells plus electric motors are 2x to 3x more efficient than IC engines, so for a given amount of travel less CO2 would be emitted.
CO2 enhancement in Los Angeles is on the order of 200 ppm. Being LA, let's assume it is all fossil fuel burning replaced by fuel cells.

So LA goes from 400 (earth average) 200 = 600 ppm down to 400 70 to 100 = 470 to 500 ppm.
If we then pull average CO2 down to a pre-industrial level of ~300 ppm, LA becomes 370 ppm to 400 ppm, or about what rural air is today. It's not perfect, but the bulk of the problem would be solved.

Certainly a hydrogen fuel cell by itself is simpler. But for mobile use a hydrogen fuel cell plus hydrogen storage plus hydrogen refilling is likely to be more complex than a direct-liquid (e.g. methanol, ethanol, hydrocarbon, starch solution) fuel cell plus liquid storage and transfer (which can use current infrastructure).
antialias_physorg
not rated yet Nov 04, 2012
The main use I'd see for hydrogen and the attendant fuel cells would be local storage right next to wind, solar and wave power generators, to capture excess and deliver it when needed to the grid production. (Or, since they are connected to the grid, that storage facility could be basically anywhere)

For vehicles I think batteries are the future.
RealScience
not rated yet Nov 04, 2012
Yes, for that use storage of the hydrogen is much less of an issue and transport of the hydrogen is a non-issue.

Currently batteries are ahead of fuel cells, but fuel cells have more room for improvement. Traditional batteries have problems compare to hydrocarbons - they carry their oxidizer with them, and they carry the spent 'fuel' with them as well. Zinc/air Lithium/air, etc. batteries avoid the former problem, but not the latter.

The convenient thing about hydrocarbons is that they both get their oxidizer from the air and release their spent fuel into the air.
Other than water vapor from the hydrogen, the only thing
less nasty to release in the air than CO2 would be N2 - to use ammonia as the carrier for the hydrogen (2 NH3 3 O2 = N2 3 H2O). But one would have to recover the energy of the N-N bond to make it efficient, and that's even more challenging than the C-O bonds in a DMC fuel cell.

djr
not rated yet Nov 05, 2012
"Hydrogen produced from energy here on Earth is an "energy carrier." So what? Every time an article on Physorg mentions hydrogen - someone has to repeat this line - as if it really matters. A battery is an energy carrier also. If you look at the fuel cost of driving and e.v. vs the fuel cost of driving an I.C.E. - the e.v. is significantly cheaper http://www.scient...r-charge So how does it really matter to state that a battery is just an energy carrier? None of us knows what we will be driving 50 years from now - or how our buildings will be heated - that makes today a fascinating moment in history.