Microalgae for biohydrogen production: technological advancement, economic potential, and sustainable energy solutions

Microalgae are promising renewable resources for sustainable hydrogen production, offering a pathway towards carbon-neutral energy systems and supporting the Sustainable Development Goals (SDGs). Biohydrogen production occurs through hydrogenase- and nitrogenase-mediated pathways, including direct and indirect biophotolysis, photofermentation and dark fermentation. In Chlamydomonas reinhardtii, the [FeFe]-hydrogenase HydA1 contributes approximately 75% of hydrogen evolution under anaerobic conditions, highlighting the importance of enzymatic regulation. This review examines the biological mechanisms and technological advances governing microalgal biohydrogen production, with particular emphasis on advanced bioreactor systems that improve light utilisation, gas exchange and reactor performance. Recent developments, including genetic engineering, microalgae-bacterial consortia and nanomaterial-assisted approaches, are discussed for their role in enhancing hydrogen productivity and process stability. Oxygen-tolerant HYDA variants in Chlorella sp. achieved up to 30-fold higher hydrogen production than wild-type strains, while plasma-generated mutants of C. reinhardtii exhibited 2.7–5.2-fold increases in yield. The economic feasibility, sustainability significance, SDG contributions and scale-up challenges associated with commercially viable microalgal biohydrogen production systems are also highlighted.