Interestingly, the average proton concentration near the cathode showed a minimum at about 5 seconds while the OH -, QH -, and Q 2-showed a maximum. The quinone dianion, Q 2-, and its singly protonated counterpart, QH -, have a pKa near 11, indicating they will be fully protonated at the typical cell pH. The consumption of protons by QH -and Q 2-therefore caused the pH increase. The simulations revealed that the transient pH increase at the cathode was due to continuous proton generation at the anode, which generated a low pH front that diffused to the cathode. Figure shows the time dependent pH averaged within 50 𝜇𝑚 of the cathode (red shaded region in Figure ) for several applied potentials and an electrode spacing of 320 𝜇𝑚. Similar to experimental observations, the pH increased for about 5 seconds and then decreased over 10 -20 seconds. The maximum pH achieved increased with increasing applied potential, also consistent with experiments (cf., Figure ). For applied potential magnitudes < -150 mV the pH decayed over times of tens of seconds, but at potentials > -300 mV the pH remained elevated over the simulation time. These features, including the maximum pH, time scale of the transient increase, and impact of applied potential, are qualitatively similar to the experimental measurements shown previously.