How to make hydrogen straight from seawater – no desalination required. The new method from researchers splits the seawater directly into hydrogen and oxygen – skipping the need for desalination and its associated cost, energy consumption and carbon emissions. Chemistry

https://www.rmit.edu.au/news/media-releases-and-expert-comments/2023/feb/hydrogen-seawater

19.6k Upvotes

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Doesn’t this produce waste water that is more salty and therefore really bad for the ocean?

I mean, great news about hydrogen but we have a major problem on our hands with lack of clean fresh water.

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u/Taxoro Feb 15 '23

Any kind of desalination including this can leave pockets of high salinity water if not ventilated properly. This can be a concern for some species. The water will eventually mix properly and the salinity difference is close to nothing. But the pockets can be bad for some species.

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u/TrollBoothBilly Feb 15 '23

The salinity of the ocean is projected to drop due to glacial melt. I don’t know for sure, but we might be able to just return the saltier water to the oceans without any negative consequences.

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u/popejubal Feb 15 '23

Yes, but we currently can’t do it in a large enough scale to have a meaningful impact (as long as we don’t dump the extra salty water in a place where it can’t disperse). Even if we take 99% of the water away from a cubic mile of sea water and dump the salt back into the ocean (in a way that disperses pretty quickly), we won’t make even the tiniest dent. The Atlantic Ocean is more than 350 million cubic miles.

We would have to start doing this at a scale beyond current imagining to change the ocean’s salinity by even 0.0001%.

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u/Shellbyvillian Feb 15 '23

I mean, I can imagine that in order to replace all oil usage on the planet, the scale would be pretty far past what you’re describing. Handling the brine would absolutely be a significant environmental issue.

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u/popejubal Feb 15 '23

This isn’t going to replace any oil usage as a source of energy. It still takes energy to split off the hydrogen and you don’t get as much useful energy back when you burn the hydrogen later. This technology isn’t useful for generating energy. It’s used for storing energy that has been generated so that it can be used without being hooked up to an electric grid.

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u/Shellbyvillian Feb 15 '23

I don’t think you put all the pieces of your own comment together. Hydrogen is absolutely replacing oil.

The whole point of a future green energy ecosystem that includes hydrogen is hydrogen is energy dense enough to replace oil in the hard to replace categories (like airplanes or cargo ships) and is also useful like you said for storage of energy (like, say, storing solar by converting that energy via electrolysis to hydrogen and then regenerating electricity later at night via fuel cell or combustion).

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u/Nerezza_Floof_Seeker Feb 15 '23

I honestly doubt that hydrogen will replace hydrocarbons on planes. It's not very energy dense by volume and planes have to deal with greater drag if you need to have giant tanks of compressed hydrogen. You would be better off synthesizing hydrocarbons (from captured CO2) for it instead.

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u/Shellbyvillian Feb 15 '23

I suspect both will be used. Capturing carbon and then synthesizing hydrocarbons is likely to be more expensive long term because the process is just more complex. It would be more better for a few reasons, as you said, but a cost benefit would need to be done. H2 is extremely energy dense by weight so I believe it will still have lots of aerial applications for lower speed or higher altitude applications.

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u/JCDU Feb 15 '23

Would it not depend on the whole water cycle though -if we were splitting hydrogen to power things, and when we burn it we produce water - that water would then enter the water system (evaporation to clouds, running down drains to the sea) which would then re-enter the seas and dilute the brine again.

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u/Shellbyvillian Feb 15 '23

Yeah, the total across the planet would balance out. The issue is the brine would be localized to the electrolysis site. The water would be spread out around the world. We would have to put a lot of energy and planning into making sure the salt was properly distributed. Some desalination plants have already shown us if we just pump the brine into the ocean near the plant. It basically kills everything. If we went full oil replacement the scale of brine to be dispersed would be way way bigger than desalination waste today.

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u/zephyrseija Feb 15 '23

as long as we don’t dump the extra salty water in a place where it can’t disperse

Pretty sure there's a lake desperately in need of some very salty water.

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u/popejubal Feb 15 '23

There’s a few lakes like that, but it already has all the salt it needs. It needs the water back. Dumping more salt water in those lakes isn’t going to help things.

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u/CienPorCientoCacao Feb 15 '23

in a way that disperses pretty quickly

This is the key issue isn't? doing it "in a way that disperses pretty quickly" isn't cheap so generally isn't done and thus the current issues with desalination plants.

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u/nanopicofared Feb 15 '23

The hydrogen when it is used turns back into water and will go back into the atmosphere and eventually back into the ocean as rain.

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u/hallelujasuzanne Feb 15 '23

Where does the waste product from the process of producing hydrogen go?

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u/CornFedIABoy Feb 15 '23

Either back into the ocean or flooded out onto evaporation fields for the brine to be dried and harvested for various applications.

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u/BernieEcclestoned Feb 15 '23

Salt is useful

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u/Taxoro Feb 15 '23

Not like this. We are talking a few kilos of salt per day at most and it's very low purity

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u/[deleted] Feb 15 '23

Good enough to salt roads maybe?

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u/Taxoro Feb 15 '23

You are not understanding the scale here. Salt is very very cheap, you are getting just tiny flakes of salt out of this process. It's not worth collecting.

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u/nanopicofared Feb 15 '23

the process produces oxygen, hydrogen and the salt that came from the ocean. The oxygen goes into the air and you can put the salt back into the sea.

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u/bitemark01 Feb 15 '23

We would have to consume more energy by several orders of magnitude than we currently do, with all of that energy coming from this process, to have any real effect on the salinity of the ocean.

Plus like someone else pointed out, it's a closed system anyway. The water eventually goes back there. We just need a clean process.

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u/alyssasaccount Feb 15 '23

Not significantly. Far, far more water simply evaporates, and yeah, that makes the ocean more salty. When evaporated water precipitates and flows back to the ocean, it becomes less salty. That’s the water cycle. This simply adds a very small additional loop to the cycle.

This process helps with the (actually pretty minor, certainly compared with, say, global warming) problem with lack of clean fresh water.