This group brings together the best thinkers on energy and climate. Join us for smart, insightful posts and conversations about where the energy industry is and where it is going.

Post

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...

  • Member since 2018
  • 1,084 items added with 147,083 views
  • Mar 4, 2021
  • 2991 views

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!"

Discussions
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? 

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

Matt Chester's picture
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 6, 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.

Travis Trent's picture
Travis Trent on Aug 12, 2021

The only problem before was the release of harmful chlorine gas into the environment.  That has been solved by special metal plates that stop them.  The only reason no one thought of it before is because OIL companies don’t want people to realize that free seawater is actually the ONLY sustainable solution to energy on this planet.   Burning hydrogen actually has positive side effects such as reversing global warming and eliminating droughts by increasing the amount fresh clean water in the air and in the ground! No solution is better.

Lamar  Dice's picture
Lamar Dice on Dec 6, 2022

I believe they are taking a very narrow view of something of this magnitude

Roger Arnold's picture
Roger Arnold on Dec 6, 2022

Could you elaborate on that statement Lamar? I don't know what you have in mind by "something of this magnitude". It's just a way to operate an otherwise ordinary alkaline electrolysis cell, but extracting the makeup water for the cell from seawater via forward osmosis. The high salinity electrolyte solutions serve as draw solutions for forward osmosis. The part that I find elegant is that electrolysis of the makeup water automatically maintains the concentration of the FO draw solution. The setup passively desalinates exactly the amount of seawater needed to supply makeup water to the electrolysis cell.

Lamar  Dice's picture
Lamar Dice on Jan 16, 2023

Seawater electrolysis doesn't require desalination. It does most of the work of removing the desolved particles and chloride"s during the process. The byproducts produced from the process, hydrogen, freshwater, minerals, metals, chlorine, hypochloris acid, sodium chloride will reduce cost associated with green renewable hydrogen. This is the game changer for renewable energy as it can be utilized 24/7 when you mix in battery storage. Fouling is only a problem with membrane type cells, as plate type cells can handle the solids and be filtered out of the water for refining. Chlorine sold as byproduct.There is much more to this than hydrogen production. Its also Co2 neutral. Picture these units in a micro grid fashion within 50 miles of coast lines generating energy.

Roger Arnold's picture
Thank Roger for the Post!
Energy Central contributors share their experience and insights for the benefit of other Members (like you). Please show them your appreciation by leaving a comment, 'liking' this post, or following this Member.
More posts from this member

Get Published - Build a Following

The Energy Central Power Industry Network is based on one core idea - power industry professionals helping each other and advancing the industry by sharing and learning from each other.

If you have an experience or insight to share or have learned something from a conference or seminar, your peers and colleagues on Energy Central want to hear about it. It's also easy to share a link to an article you've liked or an industry resource that you think would be helpful.

                 Learn more about posting on Energy Central »