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Cathodic reactions in aqueous corrosion

August 17, 2014 by Mariano Iannuzzi

The corrosion rate of a metal or alloy in an aqueous electrolyte is often determined by the kinetics of the cathodic reactions occurring at the surface. The primary cathodic reactions in aqueous corrosion are listed below.

Proton reduction reaction (acids)

$$2{H^ + } + 2{e^ – } \leftrightarrow {H_2}(g) \tag{1} \label{eq:1}$$ 

Water reduction reaction (bases)

$$2{H_2}O + 2{e^ – } \leftrightarrow {H_2}(g) + 2O{H^ – } \tag{2} \label{eq:2}$$  

Oxygen reduction reaction (acids)

$$ {O_2}(sol.) + 4{H^ + } + 4{e^ – } \leftrightarrow 2{H_2}O \tag{3} \label{eq:3}$$  

Oxygen reduction reaction (bases)

$$ {O_2}(sol.) + 2{H_2}O + 4{e^ – } \leftrightarrow 4O{H^ – } \tag{4} \label{eq:4}$$  

Equivalnet reactions

Equations (\eqref{eq:2}) is equivalent to (\eqref{eq:1}) and (\eqref{eq:4}) to (\eqref{eq:3}), assuming dissociation of water to (H^{+}) and (OH^{-}) and subtracting (OH^{-}) from both sides.[ref]D.A. Jones, “The Technology and evaluation of corrosion,” in Principles and Prevention of Corrosion, 2nd ed., (Upper Saddle River, NJ: Prentice Hall, 1996), p.5-9. ISBN: 0-13-359993-0. Buy at Amazon[/ref]

LaTeX code

## Proton reduction reaction (acids)

2{H^ + } + 2{e^ - } \leftrightarrow {H_2}(g) 

## Water reduction reaction (bases)

2{H_2}O + 2{e^ - } \leftrightarrow {H_2}(g) + 2O{H^ - } 

## Oxygen reduction reaction (acids)

{O_2}(sol.) + 4{H^ + } + 4{e^ - } \leftrightarrow 2{H_2}O

## Oxygen reduction reaction (bases)

{O_2}(sol.) + 2{H_2}O + 4{e^ - } \leftrightarrow 4O{H^ - }

Filed Under: Electrochemistry, Equations, Fundamentals, Library Tagged With: equations, equilibrium, hydrogen-reduction-reaction, LaTeX, oxidation, oxygen-reduction-reaction, proton, reduction

Professor | Director Curtin Corrosion Centre
Chevron & Woodside Chair in Corrosion | Curtin University
Adjunct Professor
Norwegian University of Science and Technology (NTNU)

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