# What is the **minimum** externally applied voltage for an electroplating setup?

I am trying to plate a piece of iron jewelry by using a silver anode and a silver nitrate solution. I am confused on how to calculate the voltage needed. Since silver is oxidized at the anode and then reduced at the cathode, is the cell potential zero?

Or am I supposed to calculate cell potential as (potential of silver oxidation) + (potential of iron reduction)? This doesn't make sense to me, because as far as I understand it, iron isn't reduced at the cathode. Please help me understand.

• @Poutnik thank you for the reply, but I am trying to figure out the minimum cell potential needed, in terms of electrode potentials. I have revised my question for clarity. Commented Nov 22, 2023 at 14:16

Better to say the minimal, externally applied voltage.

There no minimum voltage unless you mean the trivial zero voltage. In initial stage, the iron spontaneously replaces silver ions, so there is no potential barrier there. In later stages, there are two silver electrodes and there is no potential barrier either.

The minimum practical voltage is any nonzero voltage when you are able to reach the desired result during the given time interval.

Primary is controlling current density, that should be not more than (ballpark value) $$\pu{10 mA/cm2}$$. Too high values could lead to rough surface. The voltage for it is the best to be determined experimentally.

Look also for recipes for silver electroplating solutions, as it may be the key to surface quality.

A patent for cyanide-free electroplating solution recipe is:

The formula of non-cyanide silver electroplating solution consists of: Silver Nitrate 40 g/L, Sulfothiorine 230 g/L, sodium sulphite anhydrous 99.3 80 g/L, ammonium acetate 30 g/L, Potassium ethanoate 30 g/L, boric acid 20 g/L, nicotinic acid 1 g/L. The pH value of plating solution is 5-6.

Note that Sulfothiorine is the old good sodium thiosulfate pentahydrate $$\ce{Na2S2O3 . 5 H2O}$$.

There is many more recipes.

Another option is electrolysis-less plating by chemical silver deposition, many recipes available too.

• If you want to deposit a silver layer that is bright and adherent, you should not electrolyze a solution containing simple silver ions. Because the electrolysis of silver ions produce a rough deposit of silver that does not adhere perfectly on the cathode. To get a bright shiny silver layer, a complexing agent should be added in the solution, like cyanides or EDTA solutions. Commented Nov 22, 2023 at 15:12
• "In initial stage, the iron spontaneously replaces silver ions, so there is no potential barrier there." Can you explain this please? Commented Nov 22, 2023 at 15:20
• @Maurice I am well aware of it, the optimal composition of solutions for electroplating is 1/4 of chemistry, 1/4 of alchemy, 1/4 of art and 1/4 of secrets. That is why I have mentioned the electroplating solutions, perhaps not strongly enough. Commented Nov 22, 2023 at 15:25
• Iron immersed in a silver ion solution will spontaneously immersion plate silver. There is a potential but the cells are shortcircuited. The purpose of the chelating or complexing agents is to lower the activity of silver ions, ie. change the voltage, to prevent immersion plating. If done properly the electroplating gives more even plating and possibly a better shine. There is a lot more chemistry involved when one thinks about it. Commented Nov 22, 2023 at 23:28