Grotthuss mechanism

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The protonic defect migrates through the hydrogen bond network through a series of covalent bond cleavage/formation.

The Grotthuss Mechanism is the mechanism by which an 'excess' proton or protonic defect diffuses through the hydrogen bond network of water molecules or other hydrogen bonded liquids through the formation/cleavage of covalent bonds.

In his seminal 1806 publication “Theory of decomposition of liquids by electrical currents” Theodor Grotthuss proposed a unique mode of transport for protons through liquid water ^[1]. Grotthuss envisioned the electrolytic reaction as a ‘bucket line’ of sorts, wherein each oxygen atom simultaneously passes and receives a single hydrogen atom.

OHOHOH → O^-HOHO H⁺

Although Grotthuss presented his idea in the context of the electrolysis of water, and using an incorrect empirical formula of water--i.e. OH and not H₂O--his description of the passing of protons through the cooperation of neighboring water molecules proved to be remarkably fortuitous.

[edit] The anomalous diffusion of protons

The unusually high diffusion of the proton relative to other simple cations (Table 1) has motivated the formulation of a transport mechanism distinct from typical ionic diffusion due simply to the random thermal motion of molecules; i.e. Brownian motion.

Table 1

[edit] References

1. ^ de Grotthuss, C.J.T. (1806). Sur la décomposition de l'eau et des corps qu'elle tient en dissolution à l'aide de l'électricité galvanique. Ann. Chim. (Paris) 58, 54-73.