Sustainable Energy Technologies and Assessments 53 (2022) 102658 2213-1388/© 2022 Elsevier Ltd. All rights reserved. Review article Green algae as a sustainable source for energy generation and storage technologies Fernando G. Torres a, * , Gabriel E. De-la-Torre b a Department of Mechanical Engineering, Pontifcia Universidad Cat´ olica del Perú, Av. Universitaria 1801, 15088, Lima, Peru b Universidad San Ignacio de Loyola, Av. La Fontana 501, Lima 12, Lima, Peru A R T I C L E INFO Keywords: Green algae Conversion technologies Electrochemical devices Microbial fuel cells Hydrogen production ABSTRACT 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, H 2 -rich syngas, and H 2 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 super- capacitors, two of the most crucial energy storage devices available for electronic systems. The specifc capac- itance 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 H 2 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. Introduction The COVID-19 pandemic led to an unprecedented shift towards the digitalization of daily activities, like working, shopping, meetings, and recreational activities, worldwide [1]. Thereby signifcantly increasing the demand for electronic devices [2]. Along with the growth of the electrical and electronic (EEE) market, the short lifespan of these products is exacerbating the issue of electronic waste (e-Waste) [3]. This type of waste consists of multiple types of metals, toxic chemicals, and plastic materials that threaten the environment and human health [4,5]. On the other hand, fossil fuels are the primary source of energy world- wide, providing approximately 85 % of all the energy generated [6]. However, the burning of fossil fuels plays a major role in the release of CO 2 and other compounds, thus aggravating climate change and List of abbreviations including units and nomenclature: Al 2 O 3 , Aluminum Oxide; AgNPs, Silver nanoparticles; AuNPs, Gold nanoparticles; BET, Bru- nauer–Emmett–Teller; CaO, Calcium oxide; CeO 2 , Cerium oxide; CH 4 , Methane; CNTs, Carbon nanotubes; CoO, Cobalt oxide; COD, Chemical Oxygen Demand, (mg•L -1 ); CO, Carbon monoxide; CO 2 , Carbon dioxide; DSSCs, Dye-sensitized solar cells; EIS, Electrochemical Impedance Spectroscopy; EPC, Enteromorpha prolifera Derived Carbon; ESR, Equivalent Series Resistance, (Ω); Fe 2 O 3 , Ferric Oxide; FF, Fill Factor; GO, Graphene oxide; GQDs, Graphene Quantum Dots; H 2 , Hydrogen; HCl, Hydrochloric Acid; HCN, Hydrogen cyanide; H 2 S, Hydrogen sulfde; HPR, H 2 Production rate, (μmol•L -1 ); IC, Inoculated concentration, (mg Chl-a•L -1 ); HOMO, Highest Occupied Molecular Orbital; J SC , Short Current Density, (A); KOH, Potassium hydroxide; KHCO 3 , Potassium Hydrogen Carbonate; LCA, Life-Cycle-Assess- ment; LiCoO 2 , Lithium Cobalt Oxide; LDH, Layered Double Hydroxide; LiFePO 4 , Lithium iron phosphate; LiMn 2 O 4 , Lithium manganese oxide; Li-S, Lithium-sulfur; LUMO, Lowest Unoccupied Molecular Orbital; MFCs, Microbial fuel cells; MgO, Magnesium oxide; MOFs, Metal-organic frameworks; NaClO2, Sodium chlorite; NaOH, Sodium hydroxide; NH 3 , Ammonia; NaHSO 3 , Sodium Hydrogen Sulfte; Na 3 PO 4 , Trisodium phosphate; Na 2 S, Sodium sulfde; Na 2 S 2 O 3 , Sodium thiosulfate; PANI, Polyaniline; PVA, Polyvinyl alcohol; PPy, Polypyrrole; rGO, Reduced graphene oxide; TP, Tris-phosphate medium; TCO, Transparent Conductive Oxide; TiO 2 , Titanium dioxide; V OC , Open circuit voltage; Y 2 O 3 , Yttrium oxide. * Corresponding author. E-mail address: fgtorres@pucp.pe (F.G. Torres). Contents lists available at ScienceDirect Sustainable Energy Technologies and Assessments journal homepage: www.elsevier.com/locate/seta https://doi.org/10.1016/j.seta.2022.102658 Received 6 May 2022; Received in revised form 7 August 2022; Accepted 25 August 2022