Sustainable green hydrogen from algae: Assessing biological, thermochemical, and bioelectrochemical pathways

Many processes that produce hydrogen from algae also produce CO₂ and other harmful gases as byproducts. Therefore, this type of hydrogen is not classified as green hydrogen, despite being biohydrogen. The aim of this paper is to analyze and compare various biological, thermochemical, and bioelectrochemical processes that produce hydrogen from algae and identify the ones that have the potential to produce carbon neutral hydrogen. Results show that biophotolysis and bioelectrolysis produce the least amounts of CO_2, but they have other limitations. On the other hand, thermochemical processes are more time efficient, yet they consume a lot of energy and produce undesired byproducts. Detailed advantages and disadvantages, hydrogen yields, and mechanisms are discussed in this paper. To produce green hydrogen from green algae, future research should focus on developing biological pathways using genetic engineering, valorizing byproducts from thermochemical processes to enhance energy efficiency, and implementing other recommendations presented in this paper.