A CO:H2 selectivity of 0.51±0.15 was achieved after 4 h of CA at 0 V vs. RHE, which could be significantly improved to 5.41±0.53, by operating the photocathode under 0.1 sun irradiation and solution stirring (Fig. ). This is consistent with our previous findings, which indicate a threshold in the rate of CO production within the porous CoMTPP@CNT sheets. Hence, additional charges only contribute towards H2 evolution under an elevated light flux, whereas stirring alleviates mass transport limitations near the dense CNT network. A lower light flux also resulted in a steady photocurrent of around -2 mA cm -2 (Supplementary Fig. ), attaining 218±30 µmol cm -2 H2 (30.9±3.2% FY) and 337±17 µmol cm -2 CO (47.8±3.7% FY) over 24 h of CA at 0 V vs. RHE.