# In the simplest terms, what is exchange current density?

what is exchange current density, and ideally how does it relate to overpotential

I know it's related to the amount of dynamics in a reaction, so it can tell us how simple or complex a reaction mechanism is, but I don't have a clear idea of what exactly it means

What happens at intermediate potentials? The copper dissolution goes along with its exponential rate law and the deposition follows its rate law, but now these reactions are competing against each other so you macroscopically see only the difference between the plating and fissolution current densities. You might have something like $10 \mu A/cm^2$ for dissolution and $1 \mu A/cm^2$ (these are just numbers I grabbed for this argument, not necessarily true kinetics), in which case you see a difference of $9 \mu A/cm^2$ dissolution.