To exchange the air in the gas reservoir with CO2 (99.80% purity, BOC), a custom gas manifold was used. To prevent evaporation of the electrolyte the cell was exposed to a static vacuum by opening the two valves (Figure ) dropping the gas cell pressure to ~ 0.45 bar. The valve closest to the cell is then closed and the gas manifold was dosed with CO2 at ~1.4 bar. The reduced pressure in the gas cell ensures that when the valve to the cell is opened, there is a mixing of the gas reservoir with the CO2 in the gas manifold. The valve is closed, and the manifold then put back under dynamic vacuum and the process repeated 4 more times to give a 98.7% by volume CO2 headspace assuming ideal gas mixing.