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

## TL;DR

A new electrochemical method protects cyanobacteria from oxygen, enabling continuous hydrogen production using sunlight.

## Contribution

An electrochemical strategy is introduced to remove oxygen near cyanobacterial cells, allowing sustained photoH2 production.

## Key findings

- Electrochemical activation of a redox polymer effectively removes O2 near cyanobacterial cells.
- Mutant cells with a photosystem I-hydrogenase fusion enable prolonged H2 production.
- Electrons for H2 production likely come from photosynthetic water splitting.

## Abstract

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.

Photosynthetic microorganisms can be used to perform H2 evolution driven by light. However, a crucial limitationlies in the associated generation of molecular oxygen as a by‐product of photosynthesis, which compromises the activity of the biocatalyst performing H2 production, i.e., the hydrogenase. To tackle this challenge, we present an electrochemical O2‐scavenging strategy, allowing efficient O2 removal from immobilized microbial cells.