en.Wedoany.com Reported - Germany — Kirstin Gutekunst from the University of Kassel, Wolfgang Schuhmann from Ruhr University Bochum, Felipe Conzuelo from Universidade Nova de Lisboa, and their colleagues captured living cyanobacterial cells within a soft viologen-modified redox polymer coating on an electrode, forming a thin "hydrogel shell" around each cell. The team then applied a small negative voltage, reducing the viologen units in the polymer, which enabled oxygen reduction in close proximity to the cells, effectively removing oxygen from the cellular environment.

The researchers found that the reduced viologen polymer efficiently scavenged oxygen produced by photosynthesis, creating a low-oxygen microenvironment around the cells while avoiding harmful hydrogen peroxide accumulation. This kept the hydrogenase enzymes inside the cyanobacteria active, allowing sustained hydrogen production.

Experiments with genetically modified cyanobacteria were particularly successful. In these mutants, hydrogenase was genetically coupled directly to Photosystem I of photosynthesis. Compared to wild-type cells in the polymer, these mutants exhibited more prolonged and stable hydrogen production.

Under these protective conditions, the PSI-hydrogenase fusion mutants produced hydrogen stably under light, with production immediately declining once oxygen was allowed to accumulate. Since no glucose or other external fuels were added, the electrons for hydrogen production likely came directly from water splitting by Photosystem II, as expected.

Photosynthetic hydrogen production is typically self-limiting because oxygen from water splitting inactivates hydrogenase. However, this study demonstrates a practical method to decouple electrons from oxygen in intact cells. This polymer-based oxygen removal approach avoids additional fuels like enzyme mixtures and glucose, making the system simpler, more sustainable, and closer to a true solar hydrogen production device. Embedding intact cells in tunable redox polymers paves the way for scalable "living electrodes"—where cells biologically self-repair while the polymer handles electrochemical functions.

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