For the metal oxidation we use Ecu = 340 mV, and ENi = 80 mV for copper and nickel, respectively, with potentials relative to the standard hydrogen electrode (SHE). A table of the used parameters can be found in SI-1. Importantly, we use the diffusion coefficient of protons (D = 1*10 -8 m 2 /s) to determine the time constant in Equation , which is typically larger by an order of magnitude compared to values for metal ions in an aqueous solution.