Photosynthesis protein converts light to hydrogen

The technique is based on the protein photosystem I, which is part of the photosynthesis machinery in cyanobacteria and plants. With the help of light energy, photosystem I can separate charges and thus generate high-energy electrons that can be transferred to other molecules, for example to protons for the production of hydrogen.

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Working with colleagues from Universidade Nova de Lisboa, the RUB team showed that they could couple their system with an enzyme that used the converted light to produce hydrogen. The results were published online in advance in October 2020 in the journal Angewandte Chemie. According to the team, this latest study builds on previous work where photosystem I had been used to design electrodes for biosolar cells.

In the cyanobacterium Thermosynechococcus elongatus, photosystem I exists mainly as a trimer, where three individual proteins are linked together. Using a new extraction technique, the researchers were able to isolate monomers from the organism, creating a photosystem I monolayer on the electrode in which the monomers filled the holes between the trimers. The technique meant that the team was able to reduce short-circuit effects that had previously been occurring and the system achieved current densities twice as high as a system consisting exclusively of trimers.

To demonstrate one potential application of the technology, the scientists coupled it to a hydrogenase enzyme that produced hydrogen using electrons provided by the photosystem. “Future work will be directed toward even more efficient coupling between the photosystem monolayer and the integrated biocatalysts to realise practical biosystems for solar energy conversion,” the authors said in the preview of their publication. In the long term, the technique could potentially be used for the industrial production of hydrogen to power clean transportation or green gas for domestic heating.