Universidade NOVA de Lisboa (NOVA University Lisbon)

Bio‑photovoltaic systems for green hydrogen are device concepts that use photosynthetic organisms or biohybrids as the light‑harvesting and catalytic components to convert solar energy directly into chemical fuels such as hydrogen, often by integrating living cells, enzymes, or pigments with electrodes.[1][2] The studied cyanobacterial‑polymer‑electrode platform is presented as a step toward bio‑photovoltaic systems where sunlight, water, and CO₂ are used by living cyanobacteria to generate hydrogen continuously, combining biological self‑repair with electrochemical control.[1][2]

Viologen‑modified redox polymer electrodes are electrochemical interfaces where polymer matrices containing viologen groups are deposited on conductive substrates to mediate electron transfer and control local redox conditions, particularly useful for interfacing and protecting sensitive enzymes or cells.[1][2] In the cyanobacterial hydrogen system, such a polymer layer holds the cells close to the electrode and contains viologen moieties that can be electrochemically reduced to efficiently remove dissolved oxygen around the cells, thereby creating a microenvironment compatible with oxygen‑sensitive hydrogenases.[1][2]

The Photosystem I–hydrogenase fusion is a genetic engineering strategy in which a hydrogenase enzyme is covalently linked to a component of Photosystem I, enabling direct transfer of photosynthetic electrons to hydrogenase and thereby enhancing light‑driven hydrogen production.[1][2] In the reported system, cyanobacterial mutants expressing such a fusion showed significantly longer and more stable hydrogen production compared with wild‑type cells when immobilized in the protective redox polymer matrix.[1][2]

Hesse (University of Kassel) and North Rhine-Westphalia (Ruhr-Universität Bochum)