Summary: | Biophotolysis can be categorized into direct and indirect methods toward producing hydrogen gas: using sunlight and water with the use of microorganisms such as microalgae or cyanobacteria. Crucial enzyme mechanisms in photosystems I and II during the photosynthesis of water are presented, elaborating on the specific routes (with equations) of hydrogen gas synthesis. Various advantages and disadvantages about biophotolysis are also presented, reviewing many opinions. Biophotolysis is considered as one of the emerging ideas, being a sustainable and green biohydrogen gas production method, knowing the importance for further improvement toward the development of the photobioreactor (PBR) strategies. © 2025 selection and editorial matter, Mohammad Reza Rahimpour, Mohammad Amin Makarem, and Parvin Kiani.
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