A full-scale test of our different setups was assembled a week later on the 55 m 2 testing pad provided as one of three teams shortlisted for the EIC Horizon Prize final (Joint Research Center of the European Commission, Ispra, Italy, Fig. ). Accordingly, the single-sample reactor was connected to a gas bag for product collection, while the medium (32 array) and large (1010 array) reactors were connected to 1 M KOH-filled gas tanks, as described earlier (Supplementary Fig. ). The reactors were filled with 0.5 M KHCO3 and purged with pure CO2 for over 30 min on the day of the competition start.