Electrochemical Protection of Cyanobacterial Cells from Molecular Oxygen Enables Sustained PhotoH₂ Production

Photosynthetic hydrogen (photoH₂) 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 H₂. Photosynthetic microorganisms own all enzymatic equipment for this process, and the feasibility of photoH₂ production was demonstrated. However, one of the main limitations is that O₂, 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 O₂ by the integration of intact cells into a viologen-modified redox polymer. Electrochemical activation of the redox polymer allows O₂ removal in proximity to the cyanobacterial cells with a steep diffusional gradient of O₂ outside the cells. Microelectrochemical local analysis of O₂ and H₂ confirms the protection and the possibility of photoH₂ production. Moreover, the use of mutant cells integrating a photosystem I-hydrogenase fusion enables sustained photosynthetic H₂ production under these conditions, with the electrons for prolonged photoH₂ production most likely originating from photosynthetic water splitting.