While in theory this design would effectively achieve product separation from the gas mixture, in practice the system was affected by atmospheric conditions, which are not routinely considered under standardised laboratory or even controlled outdoor conditions, as well as leakage through the valves. Accordingly, overcast weather including a thunderstorm on the first day of the competition (4 th July 2022) resulted in a severely decreased light flux (Fig. , Supplementary Fig. ). Most photogenerated charges were likely employed to reduce the surface Cu oxide, instead of producing syngas, meaning that no overpressure was produced in the reactors throughout the day. Therefore, underpressure caused by the temperature drop during the night and the failure of the one-way valves led to KOH being drawn from the gas tank into the main reactors. The basic pH led to a further depletion of CO2 and hence underpressure (see inwards-curved reactor window in Supplementary Fig. ), which could only partly be compensated by further CO2 purging.