Seawater electrolysis: well, that's one problem solved

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.

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. 

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.