Difference Between Faraday Current and Diffusion Current
Core Concepts
Faraday Current: This is governed by Faraday's Law of Electrolysis, where the total charge $Q$ passed is directly proportional to the amount of substance $n$ reacting at the electrode: $$Q = nFz$$ (where $F$ is the Faraday constant and $z$ is the number of electrons). It is the "useful" current in sensors or electrolytic cells.
Diffusion Current: This is governed by Fick's Laws of Diffusion. In many electrochemical systems, the Faraday current is actually limited by how quickly the reactant can diffuse to the electrode surface, described by: $$J = -D \frac{\partial C}{\partial x}$$ In many scenarios, the Faraday current is limited by the rate of mass transport; this is known as the limiting diffusion current.
| Aspect | Faraday Current | Diffusion Current |
|---|---|---|
| Definition | It is the current resulting from the electrochemical oxidation or reduction of species at an electrode surface. | It is the current caused by the movement of ions or charged particles due to concentration gradients. |
| Origin | Arises from electron transfer reactions at the electrode interface. | Arises from diffusion of ions from regions of high concentration to low concentration. |
| Dependence | Depends on the rate of electrochemical reaction and applied potential. | Depends on the concentration gradient and diffusion coefficient of ions. |
| Nature | It is a chemical or electrochemical process current. | It is a physical transport current. |
| Example | Current observed during electrodeposition or electrolysis reactions. | Current observed in ionic solutions or semiconductor materials due to diffusion of charge carriers. |
In summary, Faraday current is associated with charge transfer reactions, while diffusion current arises from mass transport of ions or electrons due to concentration differences.
Asked in UPSE 2023 Differentiate between Faraday current and Diffusion current. Download PDF