Definition - What does Hydrogen Overvoltage mean?
Hydrogen overvoltage is the potential difference that can be found between an electrode and a reversible hydrogen electrode within a single solution. This is where hydrogen (H2) undergoes formation from ions of hydrogen.
Overvoltage typically occurs when equilibrium within a reaction does not take place. This is the case when more powerful currents pass across the boundaries of metals and electrolytes or when other electrodes are acquired.
Corrosionpedia explains Hydrogen Overvoltage
Overvoltage can also be referred to as overpotential when there is a difference that exists between cells under current passage and cell potential under the same experimental situations without electrolysis. The term overvoltage is used when the difference is expressed or measured in volts, which are an absolute value. Volts serve as the measure of rates of processes related to an electrode reaction.
In terms of hydrogen overvoltage, there is a difference in potential between the gas hydrogen or metal and an electrode in two conditions:
- When placed in a certain solution and corrosion does not occur
- When corrosion begins
When a metal or electrode is put into a solution such as water, the solution presumes a potential. If the metal begins to undergo corrosion, the metal's potential alters in value. The difference in this value of potential is referred to as overpotential.
The same thing applies to hydrogen, since hydrogen overvoltage can be described as the difference between the hydrogen’s equilibrium reactions in a solution and the hydrogen itself present in the solution when it begins to form a corrosive reaction with metal.
Understanding this particular reaction makes it possible to control corrosion rates and the effects of corrosion reactions due to hydrogen overvoltage. Hydrogen evolves into gas and reacts at different rates for each type of metal. Thus, it can be said that the rate of corrosion varies in every kind of metal.
The key here is to elevate the hydrogen overvoltage in order to slow down or halt the corrosion reaction. For instance, there are corrosion inhibitors that can make hydrogen overvoltage increase and at the same time make dissolution current decrease as it inhibits both cathodic and anodic processes.