In the voltaic pile, the cathode-half reaction was the reduction of hydrogen ions to form hydrogen gas. Where did these ions come from?

Answer 1

The hydrogen ions likely came from an acidic electrolyte solution that was placed between the two metal electrodes within the voltaic pile. As the anode-half reaction oxidized the metal atoms to release electrons, the electrolyte solution facilitated the movement of these electrons towards the cathode, creating a flow of electric current. At the same time, hydrogen ions from the electrolyte were reduced to form hydrogen gas at the cathode.