Do ion-exchange membranes *always* require ions to pass in both directions?

In an [answer](https://chemistry.stackexchange.com/questions/165668/is-there-a-material-that-ions-can-pass-through-but-water-can-t/165669?noredirect=1#comment344305_165669) to [this question](https://chemistry.stackexchange.com/questions/165668/is-there-a-material-that-ions-can-pass-through-but-water-can-t), it was asserted that:



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> Student always tend to forget that a solution must remain electrically neutral by all means. If you want a certain ion to leave water, you must provide another ion of the same charge that has left the solution.
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As per discussion in the comments to that answer, is the second quoted sentence strictly true?


Can electrical neutrality not be achieved by electrons (rather than ions) migrating one way or another to provide balance? For instance, perhaps imagine an aqueous solution under electrolysis which is divided by an appropriate membrane. A quick search brings up AEM ([Nature paper](https://www.nature.com/articles/s41598-020-80683-6)) which appears to [depict](https://www.nature.com/articles/s41598-020-80683-6/figures/1) unidirectional migration of hydroxyl ions.




Yes-but.


An inert cathode (e.g. the [standard hydrogen electrode](https://en.wikipedia.org/wiki/Standard_hydrogen_electrode) used as a cathode) does release electrons into water, but those electrons almost immediately react with the water, according to what we normally think of as a half-reaction,


$$\ce{2e- + 2H\_2O -> H\_2 + 2OH-}$$


so the effect is to produce hydroxide ions in solution (and hydrogen gas).


A series of experiments involving high-speed cameras and alkali metals have demonstrated that free electrons *are* very briefly in solution in water before reacting, e.g.



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> [Coulomb explosion during the early stages of the reaction of alkali metals with water](https://dx.doi.org/10.1038/nchem.2161)  
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> Mason PE, Uhlig F, Vaněk V, Buttersack T, Bauerecker S, Jungwirth P.  
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> *Nature Chemistry* 7(3):250-4 (2015)
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> [A Non-Exploding Alkali Metal Drop on Water: From Blue Solvated Electrons to Bursting Molten Hydroxide](https://dx.doi.org/10.1002/anie.201605986)  
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> Mason PE, Buttersack T, Bauerecker S, Jungwirth P.  
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> *Angewandte Chemie* 55(42):13019-13022 (2016)
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([Free electrons can be a stable solute for much longer in other solvents](https://en.wikipedia.org/wiki/Solvated_electron).)


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