Gas Cell Assembly: Two carbon electrodes were cut with a steel punch (0.5-inch diameter) with a mass ranging between 13.2 to 17.9 mg. The separator (GF/A Whatman) was then cut with a steel punch (5/8-inch diameter). This was then added to the coin cell (CR2032, Cambridge Energy Solutions) from the bottom up as: bottom case, conical spring, spacer (0.5 mm), bottom electrode, separator, gas-exposed electrode and then 1 M Na2SO4(aq) (100 µL) was pipetted onto the separator.