It's one of those reactions that depends on concentration and acidity, basically not going to be a concern for seawater electrolysis. Making chlorine gas is a

It's one of those reactions that depends on concentration and acidity, basically not going to be a concern for seawater electrolysis. Making chlorine gas is a pretty involved process, the NaCl salt has to be highly pure, etc. > "In all cell processes, the filtered brine is heated and passed through a bed of salt in a saturator in order to increase its salt concentration before feeding it to the electrolyzers. In some plants, the brine feed is acidified to improve the cell current efficiency. The acidification reduces the alkalinity, which would otherwise react with the chlorine in the anolyte compartment, forming chlorate." https://knowledge.electrochem.org/encycl/art-b01-brine.htm https://knowledge.electrochem.org/encycl/art-b01-brine.htm At neutral-alkaline pH with seawater you can get hypochlorite (ClO-), basically relatively weak chlorine bleach formation at 0.5-1%, this is used when seawater is used for industrial cooling systems (see nuclear power plants etc.): > "A more realistic picture of the problems DSS faces can be gained from on-site hypochlorite generators, a technology established since the early 1970s for industrial water cooling systems. There, low concentrated hypochlorite is used to avoid the growth of marine organisms as they tend to foul equipment and worsen heat transfer. The hypochlorite is formed by direct oxidation of Cl- from the filtered seawater feed. The electrolysers are one compartment cells made of titanium, and the electrodes are comprised of a titanium core with a precious metal oxide coating (Ru, Ir, Pt)." source: Hausmann et al. (2021). Is direct seawater splitting economically meaningful? (sci-hub) Hydrogen from seawater directly seems pretty speculative, be interesting if it works, you could have hydrogen production at sea maybe. Scale might be an issue (giant barges with solar panels making hydrogen for fueling shipping?)