The outdoor test in Cambridge began at noon on 21 st June 2022 with clear sky (Fig. ). A 39.539.5 cm 2 static Fresnel lens was dismounted within the first hour and not used thereafter in this test, as a drift of the focal point caused sample shadowing, which emphasizes the importance of light tracking for solar concentration. Due to leakage of KOH from the gas tank, the on-off valve was also switched off after 2 hours. Nevertheless, 1.22 µmol cm -2 of CO and 0.41 µmol cm -2 H2 were retained in the PEC reactor headspace after ~24 h. In contrast, 2.32 µmol cm -2 of CO and 5.19 µmol cm -2 of H2 were detected after ~60 h (i.e., by the end of 23 rd June 2022, Fig. ). This gradual decrease in the CO:H2 ratio was in line with the catalyst behaviour during earlier laboratory experiments (Fig. ).