Electrochemical Protection of Cyanobacterial Cells from Molecular Oxygen Enables Sustained PhotoH 2 Production

Abstract Photosynthetic hydrogen (photoH 2 ) production is appealing for sustainable energy conversion. Oxygenic photosynthesis uses water as the sole electron source and light to lift electrons to a high energy level. The energized electrons are used by the hydrogenase for the catalytic conversion of protons into H 2 . Photosynthetic microorganisms own all enzymatic equipment for this process, and the feasibility of photoH 2 production was demonstrated. However, one of the main limitations is that O 2 , which is generated as a byproduct of photosynthesis, compromises the activity of most hydrogenases and hinders the wider applicability of this strategy. We tackle this challenge, showing the protection of cyanobacterial cells from metabolically‐generated O 2 by the integration of intact cells into a viologen‐modified redox polymer. Electrochemical activation of the redox polymer allows O 2 removal in proximity to the cyanobacterial cells with a steep diffusional gradient of O 2 outside the cells. Microelectrochemical local analysis of O 2 and H 2 confirms the protection and the possibility of photoH 2 production. Moreover, the use of mutant cells integrating a photosystem I‐hydrogenase fusion enables sustained photosynthetic H 2 production under these conditions, with the electrons for prolonged photoH 2 production most likely originating from photosynthetic water splitting.