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.