Hydrogen (H2) production by photosynthetic microorganisms is a viable option for renewable energy due to its sustainability and potential for widespread application. Green algae, cyanobacteria, and purple non-sulfur bacteria have shown great promise in bio-H2 production. However, problems such as low H2 production rates and high H2 production costs continue to hinder the commercial scalability of these systems. To overcome these obstacles, genetic engineering selection of robust strains capable of coping with variable environmental conditions, optimization of growth conditions, use of wastewater, and biotechnological approaches such as immobilization are carefully considered. The aim of this review is to provide a thorough overview of the methods and developments that can improve H2 production and to highlight current difficulties and future directions for further studies.
