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Seawater electrolysis: well, that's one problem solved

Roger Arnold's picture
Director Silverthorn Institute

Roger Arnold is a former software engineer and systems architect. He studied physics, math, and chemistry at Michigan State University's Honors College. After graduation, he worked in...

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Chemistry World just released this news article about a paper describing an approach that facilitates electrolysis of salty or brackish water. The article quotes a reviewer from the University of Glasgow saying "It's definitely one of those papers that makes you wonder 'How come no one thought of that before'." I can second that reaction. I've looked into electrolysis of seawater before, and there are several issues that make it problematic. When I read of this new approach, I was slapping my head. "Of course! It's so obvious. Why didn't I think of that!"

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Matt Chester's picture
Matt Chester on Mar 4, 2021

Normally a development like this would raise a skeptical red flag-- if no one thought of it before, maybe it's because something's not quite as it seems. Sounds like you don't think that's the case here and there's more substance than hype. For those of us who have less of a chemistry understanding, is there any reason why you think this shows particular promise and why it wasn't realized until now? 

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Roger Arnold on Mar 4, 2021

You're right, Matt. In cases like this, a skeptical red flag would normally be warranted. "If it's so great, why hasn't anyone thought of it before?" The answer is usually that they have, but we never heard about it because it didn't turn out to be all that great.

Here, however, I understand quite well what the paper is talking about. There's no magic to it, it's plain common sense. At least it is, to anyone who understands electrochemistry, forward osmosis, and osmotic membrane technology. 

The likely reason it hasn't been thought of before is that it relates to a practical issue that's not very sexy. It seems very peripheral to the challenge of efficient electrolysis. And in fact it is peripheral, if one has a ready supply of freshwater feedstock. It only becomes important if one wants to electrolyze seawater. And what idiot would worry about electrolysis of seawater when a freshwater supply is easily come by? Well, if one thinks a lot about offshore wind turbines and green hydrogen ..

The author's approach is not world shaking, and it won't make a radical difference to prospects for green hydrogen. But it's elegant. I really like elegance.

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Matt Chester on Mar 5, 2021

Really interesting, thanks for your expert perspective on this, Roger! So if not earth-shaking, but still elegant and relevant, would you wager any estimates as to when this development may start to be used commercially for hydrogen production? 

Roger Arnold's picture
Roger Arnold on Mar 5, 2021

Very soon, I would guess. It could be held up by patent / licensing agreements -- i.e., who's going to end up with the rights to use it. But I don't see it needing any significant period of development before being ready for commercialization. For freshwater electrolysis, it might cut the cost of feed water pretreatment and purification by 50% or more, but pretreatment and purification are a small percentage of the operational cost of an electrolysis unit for fresh water.

The new approach will make a much larger difference for electrolysis of seawater. Currently, seawater needs to first be desalinated. With this approach, it makes no difference whether the feed water is fresh or saline. Only pure water gets through the forward osmosis membrane into the electrolysis cell.

Jim Stack's picture
Jim Stack on Mar 5, 2021

Great idea but wouldn't a membrane get all clogged with salt as the sea water passes through it. Since clean drinking water has become a crisis this could help with fresh water to bring for many.

  I heard of similar processes being used in Saudi Arabia to grow crops. But the salt was being dumped back into the sea making it even more salty. They had to stop the experiment. 

Roger Arnold's picture
Roger Arnold on Mar 6, 2021

Fouling is a potential problem for all osmotic membranes. It doesn't matter whether it's pressure-driven reverse osmosis, or solute concentration driven forward osmosis -- which is what we're talking about here. But it's not salt that causes trouble. The salt that's blocked by the membrane just diffuses back into the feed stream.

The main problem is biofilms that can grow on the membrane when the feed water isn't sterile. Precipitation of calcium hydroxide can also cause fouling. These are both issues the RO desalination plants have to deal with. They use microfiltering of feed water and pH adjustment.

The chief advantage of this approach for seawater desalination is just the elimination of the high pressure pumping required for RO desalination. The electrolyte solution of the electrolysis cell serves instead as a passive draw solution to pull in pure water through the membrane. That doesn't eliminate the need for filtering and pH control of the feed water, but it does simplify it.

Fresh water electrolyzers, BTW, also have to pretreat their feed water. Water added to the cell must be very pure, since any impurities in the feed water accumulate in the cell. 

Julian Silk's picture
Julian Silk on Mar 8, 2021

For the places where seawater might be used with this membrane, which is indeed important, you might have a higher value to desalination than producing hydrogen, per unit volume.  Where this development might be very useful is with briny water-supported oil or gas wells, whose useful life supplying fossil fuels is over or close to it.  These would be Class II wells under the EPA definition in https://www.epa.gov/uic/class-ii-oil-and-gas-related-injection-wells https://www.epa.gov/uic/class-ii-oil-and-gas-related-injection-wells.  The membrane could conceivably monetize the brine, and the infrastructure is likely to be there or much more easily constructed than with seawater, not to mention the problem with protected seacoasts.  Roger Arnold is right that this is important, but it is possible to disagree with him on where the membrane might be most economic.

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