1Biofuels, Electrofuels, Electric or Carbon-free?: A review of current and emerging Sustainable 2Energy Sourcing for Aviation (SESA) 3Pimchanok Su-ungkavatin1*, Ligia Barna1, Lorie Hamelin1 41 Toulouse Biotechnology Institute (TBI), INSA, INRAE UMR792, and CNRS UMR5504, Federal University of Toulouse, 135 5Avenue de Rangueil, F-31077, Toulouse, France 6* Corresponding author e-mail address:
[email protected] 7Abstract 8Climate neutrality is becoming a core long-term competitiveness factor within the aviation industry, as demonstrated 9by the several innovations and targets set within that sector, prior to and especially after the COVID-19 crisis. 10Ambitious timelines are set, involving important investment decisions to be taken in a 5-years horizon time. Here, 11we provide an in-depth review of alternative energy sourcing technologies for aviation revealed to date, which we 12classified into three main categories, namely liquid fuels (biofuels, electrofuels), electric aviation (all electric and 13hybrid), and carbon-free options (hydrogen-based, solar-powered). For liquid fuels, 10 pathways were reviewed, for 14which we supply the detailed process flow picturing all input, output, and co-products generated. The market uptake 15and use of these co-products were also investigated, along with the overall international regulations and targets for 16future aviation. As most of the inventoried pathways require hydrogen, we further reviewed six existing and 17emerging carbon-free hydrogen production technologies. Our review also details the five key battery technologies 18available (lithium-ion, advanced lithium-ion, solid-state battery, lithium-sulfur, lithium-air) for aviation, as well as 19the possible configuration schemes for electric propulsion (parallel electric hybrid, series electric hybrid, all electric, 20partial turboelectric and full turboelectric) and reflects upon the inclusion of hydrogen-powered fuel cells with these 21configurations.