Cathodic Half-Reaction (Oxygen Reduction)

The reduction half-reaction at the cathode where oxygen consumes electrons released at the anode and generates hydroxide ions. This is the common cathodic reaction in most water systems and is the reaction oxygen scavengers and deaeration aim to starve. The local pH rise it causes can shift carbonate equilibria toward protective calcium carbonate precipitation.

$${\text{O}}_2+2{\text{H}}_2\text{O}+4e^{-}\to 4{\text{OH}}^{-}$$

Variables

Symbol	Meaning	Unit
$O_2$	Dissolved oxygen, the electron sink	aqueous
$H_{2}O$	Water	liquid
$e^{-}$	Electrons consumed from the anodic reaction	charge
$O{H}^{-}$	Hydroxide ion produced at the cathode	aqueous

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Part of The Blueprint of Water