Photosynthetic H2 production: Lessons from the regulation of electron transfer in microalgae

Green hydrogen, produced during microalgal photosynthesis, is regarded as one of the most promising sustainable energy sources. It utilizes sunlight and water, which are essentially unlimited, and its combustion results in only water as a waste product. In microalgal hydrogen energy production systems, the sensitivity of hydrogenase to O₂ poses a significant challenge, limiting sustained photosynthetic H₂ production in microalgae. Additionally, efficient photosynthetic H₂ production in anaerobic microalgal cells is hindered by impaired electron source (photosystem II) and electron loss through the Calvin-Benson cycle, cyclic electron transfer around photosystem I, and O₂ photoreduction, which are identified as the other key challenges. Over the past eight decades, considerable progress has been made in addressing these challenges and regulating electron transfer to achieve sustainable and efficient photosynthetic H₂ production in microalgae. In this review, we discuss a range of regulatory methods for achieving sustainable and efficient photosynthetic H₂ production in microalgae. Emphasizing the significant progress made over the past eight decades, we also address current challenges and propose potential future solutions.