0x62448568…9229sent to0x8011df58…516c·#24,298,602·view on Etherscan
# Auto-ionization in adsorbed water
The oxygen and hydrogen atoms in water are charged and can bond to other charged particles. When water is in contact with a surface to which it can bond, it will tend to adhere or adsorb (ad-, to, toward + absorb) as layers with a structure very similar to ice but where the sheets are shifted by one oxygen atom between any two layers. The water molecules in this adsorbed phase can also auto-ionize, but contrary to in the liquid phase the hydroxide and hydrogen ions will not both be mobile, the hydroxide ion is stuck inside the adsorbate and only the hydrogen ion is free to move around. The asymmetry in how mobile two charge carriers are will result in that the more mobile charge carrier spreads out in all directions by diffusion, a force balanced by the attractive force backwards along the electric field that forms. The electron within the hydroxide ion can be released by oxidation of the hydroxide ions, and if there is dissolved dioxygen within the surrounding liquid water, the electrons can move after the hydrogen ions (along the electric field) and combine with them as well as dioxygen to produce water (and if this happens over a membrane there is a net loss of water where the electrons and protons moved from and a net addition of water on the other side of the membrane). The separation of charge within the adsorbate also favours nucleation of the adsorbate, as hydronium ions in high concentration in the surrounding liquid water like to bond to the adsorbate, and the electric field perpendicular to surface of adsorption also reduces any sideways motion of molecules within the adsorbate and the net force outwards towards the bulk water has a stabilizing effect (the bulk water behaves to some extent as a surface as well). Naturally, and somewhat counter-intuitively, the charge separation can therefore favor the growth of the adsorbate, and as you increase the auto-ionization (either increase the dissociation or reduce the recombination, incl. when the charges recombined by first freeing the electrons), such as by infrared radiation to increase disassociation of hydrogen and hydroxide ions or by increasing the dioxygen concentration to reduce the oxidation of the hydroxide ions and release of electrons (where dioxygen is one of the products formed), you see the thickness of the adsorbate grow.