Cathodic Half-Reaction (Hydrogen Evolution)

The cathodic reaction in acidic systems, where hydrogen ions accept electrons and form hydrogen gas. It provides an alternate electron sink when oxygen is not the controlling oxidizer.

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

Variables

Symbol	Meaning	Unit
$H^{+}$	Hydrogen ion (proton), abundant at low pH	aqueous
$e^{-}$	Electrons consumed from the anodic reaction	charge
$H_2$	Hydrogen gas evolved at the cathode	gas

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Part of The Blueprint of Water