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I'm trying to find an answer as to how lowering the pH of the CuSO4 solution during electroplating of copper affects the amount of copper deposited onto the cathode.

My very basic understanding is that if the concentration of hydrogen is too high, then there is greater competition and hydrogen will be reduced instead of the copper. (But why?)

Also the reason why CuSO4 is acidified is to prevent copper from hydrolysing from the solution as it prevents the oxidised Cu2+ from reacting with the OH- ions to form Cu(OH)2 precipitate.

However, I was wondering if this could be related to electrode potentials. That the increase of H+ concentration in the electrolyte affects the electrode potential, which is why increasing H+ increases the competition and makes it more likely for H+ to be reduced.

Im trying to explain why there is an optimal pH for the electroplating of copper and I need background information as to why too low pH or too high pH decreases the amount of copper deposition on the cathode.

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In electrolysis, $Cu^{2+}$ is reduced in two steps, first to $Cu^+$ and later on to $ Cu$. Of course $Cu^+$ is automatically disproportioned into $Cu$ and $Cu^{2+}$ in acidic conditions. But in neutral solutions, $Cu^+$ may react with $H_2O$, forming an unwanted red precipitate of $Cu_2O$. This will affect electroplating of copper.

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