Critical Anodic Current Density

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Definition - What does Critical Anodic Current Density mean?

Critical anodic current density is the optimal anodic current density seen in an active spot. It applies to alloy or metal electrodes that present active-passive action within an environment.

It is also the parameter that is utilized in equations like the Butler-Volmer and Tafel, as well as other expressions. The latter equation explains the current dependence for electrolytic processes to achieve overpotential.

Corrosionpedia explains Critical Anodic Current Density

Critical anodic current density is the current that exits without net electrolysis placed at zero overpotential. In such cases, the exchange current can be regarded as the background current, where a net current seen at different overpotentials undergoes normalization.

In a redox mechanism, or reduction, existing at equilibrium potential, the process of electron transfer goes on at solution-electrode interface occurring both ways. In such cases, the anodic current balances the cathodic current. The current that is moving in opposite directions is referred to as exchange current density.

If the potential is placed more negatively relative to the existing formal potential, the anodic current will always be lesser than the cathodic current. Being regarded as a reduction, cathodic current is considered positive. Net current density is described as the disparity between anodic and cathodic current density.

Critical anodic current density shows the intrinsic electron transfer rate that is taking place between an electrode and analyte. These rates offer insights into the bonding and structure in the electrode and analyte. For instance, the critical anodic current density that exists in mercury and platinum electrons for proton reduction vary by 10×10. This difference indicates platinum's superior catalytic properties. With this difference, mercury is more favored in terms of decreasing cathodic potentials in an aqueous environment.

Critical anodic current density is strongly affected by:

  • Nature and structure of the electrode
  • Roughness of the surface
  • Passivating oxides
  • Electro-active species nature in a solution or analyte

Less relevant factors include:

  • Temperature
  • Nature of different electrolytes
  • Environment
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