Oceans May Be Large, Overlooked Source of Hydrogen Gas

[OKIsItJustMe]

https://nicholas.duke.edu/about/news/oceans-may-be-large-overlooked-source-hydrogen-gas

[font face=Serif][font size=5]Oceans May Be Large, Overlooked Source of Hydrogen Gas[/font]

July 20, 2016

[font size=3]DURHAM, N.C. -- Rocks formed beneath the ocean floor by fast-spreading tectonic plates may be a large and previously overlooked source of free hydrogen gas (H₂ , a new Duke University study suggests.

The finding could have far-ranging implications since scientists believe H₂ might be the fuel source responsible for triggering life on Earth. And, if it were found in large enough quantities, some experts speculate that it could be used as a clean-burning substitute for fossil fuels today because it gives off high amounts of energy when burned but emits only water, not carbon.

Recent discoveries of free hydrogen gas, which was once thought to be very rare, have been made near slow-spreading tectonic plates deep beneath Earth’s continents and under the sea.

“Our model, however, predicts that large quantities of H₂ may also be forming within faster-spreading tectonic plates -- regions that collectively underlie roughly half of the Mid-Ocean Ridge,” said Stacey L. Worman, a postdoctoral fellow at the University of Texas at Austin, who led the study while she was a doctoral student at Duke’s Nicholas School of the Environment.

…[/font][/font]

http://dx.doi.org/10.1002/2016GL069066

How about that!? Hydrogen may be an energy source after all!

[caraher]

1. Not a very big source, it would appear

The paper talks about something on the order of 10^12 mol of H2 per year. From the abstract:

It has recently been estimated that serpentinization within continental lithosphere produces H2 at rates comparable to oceanic lithosphere (both are ~10^11?mol?H2/yr). Here we present a simple model that suggests that H2 production rates along the mid-oceanic ridge alone (i.e., excluding other marine settings) may exceed continental production by an order of magnitude (~10^12?mol?H2/yr).

Suppose one captures all of it and uses it in fuel cells. You'll yield electrical energy at a rate of something like 250 kJ/mol of H2 that way, so the total annual energy harvested would be 250 trillion kJ, or about 70 million kWh. Dividing by the number of hours in a year yields about 8000 kW, or 8 MW, as the effective average electrical power.

So we could engage in a heroic effort to investigate this theory, find ways to harvest the hydrogen, etc. Or build a wind farm or solar PV array of modest size to generate the same amount of electricity.

Even if the theory pans out, the challenge of capturing this small resources strikes me as far greater than, say, capturing the methane we know is bubbling into the atmosphere - and the latter would be a far greater energy source (not carbon-free, of course, but to the degree that methane is a more potent greenhouse gas than CO2, a net positive in limiting climate change).

[OKIsItJustMe]

2. Reading on in the paper…

…

Our analysis foremost leads us to hypothesize that H₂ production within oceanic lithosphere may be occurring at a magnitude higher than widely recognized (~10¹² instead of ~10¹¹?mol?H₂/yr). Since we do not account for H₂ produced by serpentinization in other recognized marine settings (see introduction), the actual rate may even be higher than the 1.2?×?10¹²?mol?H₂/yr we estimate here. Our hypothesis warrants future research but at present seems reasonable in light of what is known about the magnitude of other H₂ related lithospheric processes. …

However, yes, producing the H₂ by other means would likely be better in the long run.

[caraher]

3. It's interesting science

And it's also still possible there are trapped deposits somewhere, that could be tapped as a non-sustainable, one-time thing. And talking about energy boosts interest in the research. Good publicity move.

Just don't expect that we'll all be driving fuel cell cars powered by this "free" hydrogen!

[nationalize the fed]

4. k&r

Oceans May Be Large, Overlooked Source of Hydrogen Gas

Of course they are. Even without these new found deposits, there are 22 litres of Hydrogen in a single TABLESPOON of water.

And with solar energy prices reaching .03 cents per kWh and below, it's almost free to split the H2 from the O now. In 5 years- everyone will be talking about Hydrogen. It's the Next Big Thing.

[OKIsItJustMe]

6. There is a very big difference here

As water, yes, the oceans contain lots of H₂O.

Combining H₂ and O₂ produces water and a lot of energy, which can be used to propel a rocket, or power a car. However, reversing the process, splitting H₂O to produce H₂ and O₂ requires every bit as much energy (and more.)

It takes energy to produce fossil fuels from the ground, but less energy than is produced by burning the fossil fuels. They are a net energy source in our experience.

Producing H₂ from H₂O requires more energy than you get back by burning the hydrogen. It’s a net energy sink, but, perhaps useful as means to chemically “store” energy (much like a battery.)

This study suggests that there is molecular hydrogen, H₂, trapped in rock, which, perhaps, could be produced like fossil fuels.

[caraher]

7. 22 liters per tablespoon? 0.03 cents per kWh solar?

The relentless hydrogen boosterism is expected, of course, but this kind of demented mashup of units to make a point that is, at the very best, highly misleading, still managed to surprise me.

Thanks for reminding me of the infamous Verizon misadventure with units...

[NNadir]

5. Were this a significant amount of hydrogen, the Earth would have lost its water billions...

...of years ago, for the same reason that while helium is the second most common element in the universe, it's relatively rare on Earth.

All of the helium on Earth comes from the decay of uranium and thorium. When it leaches from rock into natural gas deposits it can be isolated. However once it's released into the air, it ultimately boils off into space, since if one utilizes the Maxwell Boltzman distribution for the gas, one can observe that a significant portion of the gas molecules exceed the escape velocity of the earth at higher altitudes at terrestrial temperatures. (The velocity of a gas at a given temperature is inversely proportional to its mass)

¹H₂ gas with has half the mass of helium, and thus will have a higher fraction of molecules exceeding the escape velocity.

Effects like this are thought to have participated in the dehydration of Mars. Since that planet lacks the capacity to shield itself from radiation, lacking oxygen, atmospheric water would have been subject to radiolytic water splitting, with the resulting oxygen reacting with surface iron (giving Mars its red color) and the hydrogen boiling off into space.

It is probable that Earth's higher mass and escape velocity (as well as it's significant magnetic field) prevented all of its water from similarly boiling off into space before oxygen appeared in the atmosphere when photosynthesis began.

Since we are happily destroying the ocean life while we wait for all these "solar breakthroughs" to pan out - even if they never actually do so - and because we are working as hard as we can to destroy Earth's ozone layer, we might expect that oxygen will become depleted on this planet again, helping us to hope for the boiling off of our planetary water sooner rather than later.

Happy Friday.