Green algae as a sustainable source for energy generation and storage technologies

In light of the environmental and human health threats posed by electronic waste, taking advantage of the properties and compounds of green algae presents timely and sustainable energetic alternatives. This review is focused on the technologies developed to use green micro- and macro-algae for energy storage and generation. The main applications of these algae-based technologies include the extraction of bio-fuels and the fabrication of energy storage and energy conversion devices. Bio-oil, H₂-rich syngas, and H₂ are among the essential bio-fuels produced from green algae feedstock. The hydrogen production of these green algae-derived bio-fuels ranges from 16.8 to 84.1 %. Cellulose, activated carbon, among other materials and compounds extracted from green algae have been used to fabricate electrodes and separation membranes which are part of batteries and supercapacitors, two of the most crucial energy storage devices available for electronic systems. The specific capacitance and current density of these devices have reached 1617 F/g and 31 A/g, respectively. Natural dyes extracted from green algae have been proved to be suitable for the development of novel dye-sensitized solar cells (DSSC), with an open circuit voltage in the range of 0.62 V – 0.75 V. In addition, microbial fuel cells have been tailored to use the oxygen released by the photosynthetic reactions of algae growth as an oxygen source for the cathodic reactions that convert H₂ into electricity. Although a wide range of energy applications of green algae are presented, there are still many challenges to overcome before obtaining commercially viable and scalable technologies. Further research needs are discussed.