Electrodes are casted on standard current collectors, in this case aluminum foil, while some other designs cast on porous membranes . The use of standard current collectors also has the advantage of making the system more comparable with other experiments. The working electrode current collector is structured with a gas flow field. To improve gas diffusion from the electrolyte into the carrier gas stream, the working electrode current collector foil has been perforated with a needle roller. A flow diagram of the overall system is provided in Figure ). Helium is used as a carrier gas with a flow rate of 5 NmL h -1 . It is fed into the system via a mass flow controller. The second mass flow controller is an inlet for calibration gas mixtures. This allows to calibrate the system with adjustable molar fractions of calibration gases by further diluting the calibration gas mixture with pure helium. 2)